Marzocchi 43mm fork design and impact of oil level on spring rate

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Disclaimer: I'm not a suspension expert, just curious.  If any experts would like to comment on my rambling, I'd be more than happy.  Plus I keep updating the text, now into its third day of writing and editing based on some more info from Rick.  Also with Rick's replies I have realised that this leg is (possibly, maybe it never had it) missing the inner spring guide, which is a plastic slotted sleeve that goes over the damper rod above the cartridge to help support the spring from the inside.  See the circled part in the parts catalogue diagram below.  Also note that this diagram is shown for all the 43mm non adjustable Monster forks from 03 - 07 that I looked at, and is possibly a Showa from memory with the spring located slotted collet.

There was a post on the Monster Forum about the Marzocchi 43mm non adjustable forks fitted to a M800ie.  I have an old M400ie fork leg at work, one with nasty external damage that I expect came from rubbing against something in the container on the trip over from Japan.  So I figured I'd strip it and have a look at the valving system.

Typical of the springs Ducati fit to many of the non SBK models, it is a two stage style.  I wouldn't call it progressive, as that implies something some see as desirable and useful.  Don't see either myself.

In terms of spring rate, you get an overly soft spring until all the tight coils have bound, then you get a fairly sudden change to a much harder rate.  Spring rate calculations are based on the wire diameter (bigger = stiffer), coil diameter (bigger = softer) and number of coils (more = softer).  So when the tight coils bind, you go from 22 to 14 and the rate changes.  The measured graph is as below, mm of compression along the bottom, kg up the LH side:

Adding two constant gradient lines to the graph shows the rate change more clearly, starting at 0.63 kg/mm and changing at 90 mm of compression to 0.91 kg/mm.  In a Monster I'd usually fit 0.85 to 0.95 kg/mm springs, depending on rider weight.  I don't understand why they choose these springs.  But, if you cut off the tight section, you get a 0.9 ish kg/mm rate spring that is quite usable (possibly a bit short though, the Showa ones are better to cut down in my experience).

The springs as fitted have 20mm of preload.  With what I find as your average rider on board they'll give 45 to 55 mm of sag.  Which means they'll be compressed 65 to 75 mm and have 42 to 49 kg of load on them.  More on that later.

On to the internals.  The cartridge has heavily swaged ends, so is very much non rebuildable without getting medieval.  And destructive.  But it's always nice to see what's inside, and the pipe cutter was happy to accommodate.  I didn't take a photo of the assembled cartridge, I forgot.  The following photos and text are a fairly basic description of the cartridge system.

The cartridge itself is a steel tube with a rod inside it.  On the end of the rod is a piston, in this case carrying a rebound shim stack.  The bottom of the cartridge is at the RH side, and the valve on it is simply to allow oil to flow into the cartridge through the large round hole you can see.  The small round hole is to allow oil to leave the cartridge on compression.  There isn't any real compression damping function in the cartridge.  When being compressed, apart from the small hole, the oil flows through the piston via large ports that have a flat plate over them.  The plate is to stop the oil flowing back through these holes and bypassing the shim stack when the piston is rebounding.  While this flat plate is held in place with a soft spring, it's only there to keep it seated.

The four small holes you can see are the rebound ports.  The four shims to the right are the rebound shims.  They act like a circular leaf spring, and the oil being forced through the ports as the piston moves bends the shims up to allow itself to pass through.  On the left is the compression plate.  The photo below shows the piston ports.  The large ones are the compression transfer ports.  The size of the rebound ports can be a restriction in themselves, and is why lighter oils are often used when revalving work is carried out.  One of the advantages of the Race Tech Gold Valves, for instance, was the increased flow area.  More flow area means you need heavier shims (usually just the same as shown previously, but stacked with more layers) to handle the increased flow, but also increases the ability to widen the range over which you can have effective control of the damping rates.

So, to summarise.  The fork cartridge has a basic rebound damping shim stack and no compression damping function.  I have heard of the damping being different left to right in these forks, but the parts catalogue shows only one cartridge part # for both legs.  Having one compression dedicated leg and one rebound leg is not a new idea, but it is becoming increasingly popular again.  For example, the Showa BPF (big piston fork).

I have read posts from Rick at Cogent Dynamics saying that, in his opinion, the valving in these forks is quite good for what they are, and certainly equal to the Showa non adjustable forks also used by Ducati during the era.

I thought I should ask Rick, instead of just misquoting him.  His reply was:

"Who knows what I said??? ;-)  It is true that while the Marzocchi fork is not serviceable or revalvable, the damping design is better than the crappy Showa, even the adjustable ones from the era.  The Showa can be fixed but the list of crap wrong with those cartridges is a long one.  The adjustable ones on many of the late 90s to even now for all I know are super crappy in that the rebound adjuster bleeds cartridge pressure into the cap where it effects compression damping as much as rebound.  Also, from what I see on the dyno, the damper rod pumps its self up with air and causes lag in VERY hard use.

We do have our own replacement cartridges that fit right in to the Marzocchi  forks making them very good and also adjustable if wanted.  We have a couple sets running around down there on the bottom of the world with you.

It is interesting if you also plot the top out spring effect at the beginning of travel (before the sag).  When we fit spring to those forks we reduce the diameter of the spring guide (depending on the wire diameter of the new straight rate spring).  The cartridge you took apart has a base valve that looks much more simplistic than the one I had apart.  The one I had used a standard type shim stack/ valve and check plate on the base valve.  I have some intact 800 SS cartridges here but I have to dig through my Damper Dynamometer files to see if and what I have of dyno reports on those…

The spring/oil height combo really can improve the fork feel, those progressive wound springs kinda work some for everyone but not too good for anyone.  Not too a bad choice if you're Ducati, I would say."

Moving on, the next stage, and something that I took the chance to spend a couple of hours doing today, was to check the effect of oil height on effective spring rate.  In this case, effective spring rate refers to the impact of increased air pressure inside the fork leg as the fork compresses.  The air gap inside the fork leg decreases as the leg compresses, leading to a pressure rise.  Well, unless the seals are leaking.  This pressure acts equally on and perpendicular to all surfaces, so it tries to expand the tubes as well.  But what we are concerned with is the pressure acting on the top of the oil (assuming in this instance the top of the outer tube is the fixed portion of the spring system), which pressurises the oil (which is not compressible, unlike air) and thereby transmits that force to the bottom of the fork leg, just as the spring does.

I have an Ohlins chart for this from their manual for the R/T 43 mm forks, as below.  In this application, the oil level is specified with the springs fitted.  Compared to the Monster settings below, where the oil level is set without the spring fitted, the spring fitted will change (raise) the oil level, probably in the range of 40 to 60 mm from my experience.  This system works in the Ohlins R/T 43 because the spring sits at the bottom of the forks and is covered by the oil.  In many other forks, the spring sits at the top and protrudes from the oil, both making measuring difficult and introducing another variable (being spring design/configuration).

I did this by reassembling the fork (tack welding the cartridge) as if it were being fitted to a bike and then compressing the leg in the same way as I test springs.  This way I measured the overall load on the leg as it was compressed, again in 10 mm steps.  I ran 3 different oil heights with the std springs, 105, 125 and 145 mm, as measured without springs, preload tubes or seats.  105 mm is the specified oil height for these forks.  Then I replaced the springs with some linear rate ones (oem ST4 from memory) and ran the test again with an oil height of 125 mm.  This was as much as time allowed.

There is a small amount of obviously incorrect data in the results (bumps in the graphs), but overall the results were rather interesting.

The first graph shows the overall results, then I'll break it down.  The "spring only" curves are for the springs tested out of the leg, and this is the base rate so to speak.

The three oil level settings with the original Monster springs is as below, with the Monster spring only as a comparison.  I have offset the spring only curve based on the 20 mm spring preload, to try to be a little more accurate (?).  And I have modified the data so all the curves start at 0, just to make it easier to read.  I'm not sure if how I have done it is 100% correct, but it gets a bit confusing.  The 125 mm curve is a bit high up to 50 mm of compression, so there's a little error there.  But the shape of the curve is the main point of all this.

As you can see, even 145 mm oil height increases the spring rate at 120 mm compression from 0.91 kg/mm to around 3 kg/mm.  The 105 mm oil height curve ends at 110 mm compression simply because before I got to 120 mm compression the total load went over 200 kg and my scales turned off.  At that point the effective rate is over 4 kg/mm.

Next I replaced the original spring with a linear ST series spring measured at 0.83 or so kg/mm.  It's shown in comparison to the Monster spring below.  As the photo shows, the linear spring at the bottom is longer.  In terms of material volume, a basic calculation shows the volume of the linear spring is 41.5 cc and the Monster spring 42 cc, an almost negligible difference.  But the black plastic oem spacer at the RH end of the Monster spring is 110 mm long, 38 mm OD and 4 mm thick.  Its volume is 47 cc, which is significant.  This sort of thick plastic spacer is common in the Marzocchi forks, whereas the Showa have a thin walled steel tube with nylon end supports.  The piece of aluminium tube I cut to preload the linear spring is 32mm od and 1.6mm wall thickness.  It's what I use for new preload tubes in place of the steel originals when replacing springs in Showa forks.  The piece shown has a volume of 4 cc, so the total volume of the Monster spring and spacer combo is around 89 cc, as opposed to 45.5 cc for the linear replacement.  That 43.5 cc difference is significant, as the next graph shows.  Assuming the ID of the fork tube is 39 mm, it calculates to an oil height difference of around 40 mm.

Both these next curves are for 125 mm oil height, green is the ST series linear spring, purple the oem Monster spring.  The 27 cc greater spring/spacer volume of the oem parts relates to maybe 30 mm in oil height at a guess, which is another variable when replacing springs.  Dropping the oil level with the oem setup to 160 mm or so might give an equivalent air gap change.  Although, as the oem spring volume is more concentrated at the top (you always fit a non linear spring with the tight section at the top to reduce unsprung weight), this may also lead to the air gap volume decreasing at a higher or accelerating rate with increasing compression compared to the linear spring, again compounding the difference.  As ever, it's a case of the unknown bringing you undone.  Or just confusing you.

Adding the Monster spring with 145 mm oil height curve in black shows this more clearly.

In hindsight I should have pulled a new 0.90 kg/mm spring from the shelf to use for this comparison.  The springs I usually use are between 260 and 297 mm long, depending on brand.  But, unless I used a thick plastic spacer, I'd possibly end up with an even more varied result if I had a longer aluminium preload tube.  The plastic tube is hard to find in this sort of size (38mm od ish) and suitably thick wall thickness, and the closest thick wall orange electrical conduit is on the small side OD wise for my liking.

The next graph sums up my frustration with the way the Ducati forks are set up as they leave the factory.  The red curve is oem at the 105 mm oil height spec and orange the ST linear spring with 125 mm oil height.  The green line represents 30 kg loading, which equates to 40 and 30 mm compression respectively, chosen because it represents an approximate loaded sag setting.  The blue line is 145 kg, which is the force at 120 mm compression with the linear ST spring.  I chose this as it is probably a good representation of the max load the fork will see (they bottom at 122 mm travel), and it illustrates my point nicely.

If we assume 30 and 145 kg represent our end points in on-road use, then the oem setup operates between 40 and 105 mm of travel, or 65 mm total effective travel.  Over the same load range the linear ST spring uses nearly 90mm of travel.  This is the point that I don't understand.  Why make use of a little over half of the available travel?  Using more of the travel with an overall softer rate at the end point will help it absorb bumps when loaded heavily.  Specifically, braking hard into a bumpy corner.  With the oem setup, the effective spring rate in that case would be over 3 kg/mm.  With the linear setup, it is half that or less.  This will allow the suspension to work, whereas the oem setup will be more likely to just bounce over the bumps and unsettle the bike.

I believe this is why sport bike forks run linear springs and are going to lower oil levels, increasing the compliance at close to full compression.  From a design point of view, it may be the separation of influences that is the big plus.  Much like the Showa BPF damping separation, anything that can be done to clarify influences and reduce interference between them is desirable from an engineering stand point.

Bringing the progressive spring point up again, the above example leaves me with no understanding as to why they are so popular.  The effective spring rate in the oem Monster fork changes by a factor of 7 or so over the total fork travel, and leads to a reduced range of travel.  It seems to me that most progressive springs start out too soft, which just gives you excessive sag.  Excessive sag is just using up one end of the travel range, for no reason I can see.  Even the linear ST spring gives an effective spring rate change of a factor of 2 or so over the total travel range with 125 mm oil height.  So I guess the question is "how much progression is desirable?"

The linear spring gives an effective progressive rate as tested, and raising the oil level would increase that just as effectively as changing the spring would.  The big qualifier there being "within reason".  The relationship between internal component volume and oil height will also be relevant.  All forks will be different in that aspect, and the results in this report apply only to these forks.  I'm sure the Showa forks, with their reduced spring and preload spacer volume, will require higher oil levels to show the extreme increase the 105 mm oil height does in these Marzocchi forks.  Going back to the 90's Monster 40 mm Marzocchi and 41 mm Showa forks, oil levels in them were 80 to 90 mm.  And there is an early M900 service bulletin to add another 30 ml of oil to them to reduce dive under hard braking.

The other side of that is lowering the oil level until it starts bottoming out, then go back up 10 mm.  But the spring is the first thing to get right.

One thing some do to try to help a too soft spring is to increase the preload.  I have been told that a soft spring overly preloaded will give a harsh feeling towards the end of the travel, so I made another graph with the oem Monster spring preload increased.  I think it's representative and reasonably accurate.

I've added 13mm of extra spring force to the measured load to give curves for 105 and 145 mm oil height and compared these to the ST spring with 125mm.  As you can see, with more preload and less oil it's not too dissimilar to the ST curve in the working range.  I might try to physically measure this setup, and maybe drop the oil level even more.

The extra preload may help reduce the dive under brakes too.  Without any real compression damping function in their design, any help you can get there is a bonus.  Raising the oil level will possibly help that too, but given these results it's a variable I'd be going the other way on for all the other requirements.

Which is not to say that the ST curve is ideal.  It's just more like I would do myself, but now I may think about that more too.

I'm very pleased with the test results.  I wasn't expecting such an extreme rate change with the higher oil levels.  I have heard of people saying you can restrict overall fork travel with oil level, but I think personally I'd rather do it with spring rate.  On a bike that is designed from a marketing viewpoint, such as the Ducati Hypermotard for example, the suspension setup (soft, long travel) is what is expected by the market, not what is desirable.  and you could certainly raise the oil level on those forks to reduce the total usable travel.  But you're still stuck with the excessive sag and oft associated dive under brakes, and that's the thing that annoys me the most.  Replacing the springs and leaving the oil level at a normal height would give a much better result in how the bike performs.  In my opinion, anyway.

As I said, I'm no suspension expert.  But I do find it interesting up to the points that I can understand.
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Closed for the holidays

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I'm closed for the holiday season until Monday, January 13.

Best wishes to all for whichever holiday or not you choose to celebrate.

Many thanks for your business and support over the past year, and looking forward to not stuffing it up in the future.

Brad
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Good article on fork design from Paul Thede at Race Tech

Someone on Ducati ms linked this article by Paul Thede of Race Tech about the differences between damping rod (old style right side up) and cartridge (nearly all USD) fork designs.  Nice and simple explanation.

http://racetech.com/articles/CartridgeForks.htm
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Closed until Monday, October 7

New reports and organisation on the Reports page

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I've put up a new report about Moto Guzzi Daytona RS and have also moved some blog posts over to proper reports, such as the Throttle Position Sensor setting procedure for California and Bellagio and Tuning an 851 SP. Or, the things you don’t know you don’t know..
Also, at the start of appropriate sections, I've added a "collected blog posts" report to link all the blog posts.  So that way you don't need to scroll through all the blog posts to try to find stuff that applies to what you're looking for.

For example, at the start of the Ducati 2 Valve section there's 2V Ducati fitted with Keihin FCR carbs - Collected blog posts  
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Mounting pod filters on a Ducati 4V intake

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Some time ago I tuned an 888 fitted with a hot 955cc SP5 style motor.  One of the changes was some throttle bodies bored to 54mm.  Amongst other agro, I found the air filter was sitting on the (oversized carbon) horizontal cylinder inlet trumpet.  So I suggested to the owner that maybe fitting some pod filters over the trumpets could be a good idea.

To mount the trumpets I used some muffler end caps sourced from a local exhaust manufacturer.  These had (from memory) an ID of around 58mm and an OD of 100, over which I fitted some K&N RC-5057 filters.  Actually, now that I look at the photos, maybe the OD was smaller and I fitted some aluminium tube to bring the OD up to 100mm.  I forget now.

Photos below show the fitment.  I cut the front out of the airbox, so from the sides it look std.  Due to further agro with the 54mm throttle bodies it ended up having std SP5 throttle bodies fitted, so the whole exercise was a little moot in the end.  Not sure if it helped or not.

But the main reason I'm posting photos is for a fellow on the Monster forum, who want's to put pods on an S4 Monster.  I would always recommend keeping the trumpets in this instance.  Removing the trumpets and fitting pods direct to the throttle bodies never seems to work well.

The reason there is a space under the trumpet mount above the throttle body is that the 888 airbox is held on by sitting between the trumpet and the throttle bodies, unlike the later bikes where the trumpets twist and lock into the throttle bodies and the airbox is frame mounted.

Ducati 2V cam comparison: pre 2002 3 bearing cams vs 2002 on two bearing cam

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Someone asked me about fitting 800 cams into a 750 motor, so given I have 620 and 750 cams easily at hand I figured I'd take a photo and make it a bit clearer.

Prior to the 620 and 800 motors being introduced, all the cams since Pantah run with two bearings at the pulley end and one in the cap.  Part of the 620 and 800 minor redo was to drop one of the pulley end bearings.  The cap end is also different, with about 3 or 4mm added.  The form is the same, it's just longer.

To fit a 3 bearing cam into a 2 bearing motor you just need some spacers to position the cam correctly at the pulley end, as the cam is pulled to the pulley end when tightened.

But to fit a 2 bearing cam into a 3 bearing head you need to grind the cam to locate the larger, inner bearing at the pulley end (as it sits next to the lobe) and also shorten both the snout and spacer section at the cap end.  I don't think you could just add another bearing further in at the pulley end, as the head is machined to locate the outer bearing in its position.  I think, I'd have to look now that I'm saying it to remind myself.


Anyway, photo below.  750 at front, 620 at rear.

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Tuning an 851 SP. Or, the things you don’t know you don’t know.

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The first time I played with an 851 SP (SP3), I ran it on the dyno then had Duane make me an eprom as required.  But, it didn’t seem to work as I anticipated it would.

 

Next time it was an SP4, fitted with an FIM additional memory board in the P7 ecu.  Although I made many changes across the fuel mapping, and generally made the low speed running much nicer, the WOT fuelling didn’t change as I had expected.  Specifically, when I made zoned fuelling changes with the FIM hand held terminal the air/fuel ratio changed as expected.  But with the changes converted to actual mapping with the additional memory board (too much to explain), the air/fuel ratio didn’t change in some places.

 

Sometime later, when I had software to look at the fuel and associated maps themselves, I noticed a couple of things that explained much of this.  And introduced me to a concept I now appreciate well: it’s what you don’t know you don’t know that brings you undone.

 

First up, the fuel map on the SP2/3/4 shows the first issue.  Some background: the SP was the hot one, with the flash “race” bits such as dual injectors with staged operation.  This feature in particular really peaked people’s interest and really helped build the folklore.  Unfortunately, it didn’t quite work as expected, both literally and mythically.  As introduced on the 1988 851 Strada and Kit, the black or red (IW042) dual injectors were used up to SP4.  The same injectors were used on the factory race bikes (Lucchinelli and Roche Replicas, etc), but with the fuel pressure raised to 5 bar from the std 3 bar.  Which made complete sense once I’d seen the fuel map.  Incidentally, the P7 ecu only has one fuel map, not main and offset like the P8 and later ecus.

 

Below is the fuel map from the 888 SP4 037 eprom, in hexadecimal form.  For those unfamiliar with hexadecimal, it is a number system with a base of 16, not 10.  Like decimal, it has 0 to 9, but then above 9 there is A to F.  In 8 bit hexadecimal, you get a pair of digits for each number giving a total of 256 numbers.  But, you need to remember that 0 is a number, so the range is 0 to 255.  Like decimal is base 10, with a range of 0 to 9.  So 00 is 0, 10 is 16 and FF is 255.  The fuel maps in P7, P8, 1.6M and 1.5M are all 8 bit, although the rpm values are 16 bit on all from memory, meaning they are made up of two pairs, such as 3F4A.  The maps in the later 5.9M and 5AM on are 16 bit as well, giving a maximum map number of FFFF, or 65535.  The red numbers at the RH side are degrees of throttle opening, the blue number along the bottom rpm x 100.

 

The main point here is that the top line (WOT) you can see FF at 8,000 rpm, along with FA at 7,000 and FC at 9,000.  This means that the biggest number available is being used.  However, to clarify a point, this is not the same thing as duty cycle.  Duty cycle is the time the injectors are open expressed as a % of the total time available to open them.  The dual injector throttle body report deals with this more.  Going from FA to FF is only a 2.4% change, so there’s not much more at all available over the range in which the torque peaks.

What FF means is that the software can’t have a longer pulse width on the fuel map.  In the case of the Weber systems, FF means 17 milliseconds.  Why 17ms I don’t know, but that’s what it is.  And each increment is 17/255 or 0.0667ms.

In the case of the dual injector P7 and P8 bikes, once the pulse width duration goes over a certain time as defined in the software, the duration is cut in half and the second injector is opened as well.  Meaning each injector can be opened for a maximum of 8.5ms.  If you have a look at the dual injector report you can see the implications and benefits of that.

But, the issue the FF brings in this case is that, with std mufflers, etc, the SP2/3/4 is already using the maximum amount of fuel per cycle at the torque peak.  Meaning that when you open it up and decide you need more fuel, you can’t have any.  So, by definition, any std dual (black or red) injector, A cammed 851 kit to SP4 will be lean around 7 to 9,000 rpm.  As an aside, the 851SP of 1989 ran single green IW031 injectors, and would be fine.

How do you get around this?  Well, there are two obvious ways, and two not so:

1.       Fit larger injectors.
2.       Increase fuel pressure (ala race kit).
3.       Offset environmental trims.
4.       Fit an add on unit like a PC3, Bazzaz, Dobeck.

Why option 1 was never acted on until the change of throttle body design with the 888 I don’t know.  It’s obvious, as it was from the start: the 851Kit fuel map has FE on it.  And they were fitting the larger IW031 green injectors to the 1989 851 and later 907.

Option 2 was the route taken for the 851 Kit, and the race prep notes mention the 5 bar fuel pressure regulator and possibly also the special (read ‘it’s expensive because it’s race’) fuel pump to knock it out for long periods.  The road bikes run 3 bar, increasing to 3.5 bar gives you 8% more fuel, 4 bar gives you 15.5%.  But, you don’t need the blanket change that a fuel pressure increase gives you, you just need more in a certain range.  Although for many, especially back in the day when tuning options and knowhow were very limited, bumping up the fuel pressure would have worked just fine.

Option 3 I can’t confirm, but from what Duane Mitchell explained to me some time ago it should work.  Those familiar with 851 are most likely aware of the 008 and 009 eproms.  008 is for open airbox lid and std mufflers with baffles removed.  009 is for all std.  The difference is 6%, and is achieved not by richening the fuel map, but by increasing the ambient air temp trims by 6%.  This blanket change is much the same as increasing the fuel pressure from 3 to 3.4 bar.  Not very precise, but the 008 does seem to work quite well.  Of course, if you set the idle mixture via the idle trimmer with the 008, you will reduce the lower throttle enrichment considerably.

The further implication of option 3 is that you can use the environmental trims to overcome the FF issue.  This is why adding fuel via the FIM hand held terminal worked on the dyno.  The hand held terminal’s input to the pulse width is added well down the calculation stream, and the 17ms restriction is only on the actual map number.  So I believe what was initially 17ms can be trimmed up to (theoretically) the maximum allowed by the cycle time once the pulse width calculations begin for any given cycle.

The graph below shows the air/fuel ratio for the SP4 I ran back in August 2001, the first time I had used the Dynojet air/fuel ratio set up.  And, in hindsight, there was a very obvious reason why it confused me enough to pull the sensor tube out of the muffler after my first attempt at putting changes into the additional memory board.  I wish I hadn’t now.  But, anyway, blue is the base fuelling on the eprom fitted to that bike (BMM01), which I now know had FF at 6,500, 7,000, 8,000 and 9,000 rpm.  Red is with +10 via the hand held terminal.  Clearly, it’s a consistent +10 change across the range, so the hand held terminal is able to do what an eprom can’t.

 

I haven’t tried this though.  I was going to, but the time it takes to play with this sort of stuff is time I just don’t have these days.

 

Option 4 is simply because there is more time available (much more), so even though the PC3, etc, can only be connected to one of the two injectors per cylinder, it will help.  The point is that not a lot more fuel is needed, but it’s enough to be a bit of an issue.

 

Moving on, the environmental trim tables throw up some more issues though.  The SP3 ambient air and engine temperature trim tables are show below.

 

While the engine temp trims are as expected, and with the engine being water cooled, relatively stable and inert during use, the ambient air trims are a problem.  You can see that at 17 degrees, the correction is +3.1%.  At 29 degrees, it’s -3.1% and at 41 degrees it’s -6.3%.  As it turns out, these corrections are chemically correct for the change in air density due to temperature.  But, as ever, it’s the theory versus application thing that brings us undone.

If the bike is stationary or moving at low speed and hot, a lot of radiated heat comes up into the airbox.  Where is the ambient air temp sensor on an 851 and 888?  In the airbox.  So it will read the radiated heat and act on it.  If you pull up at a set of lights on a 17 degree day, by the time you take off again a couple of minutes later the airbox temp may certainly have hit 41 degrees or higher.  In which case, your fuelling when you take off will be 9.4% leaner than it was when you pulled up.  Once the bike is moving the airbox temp will quickly drop again, but by that point you’ll have stumbled or stalled and grabbed a handful of throttle to get the thing going and before you know it you’ve got a reputation for not liking traffic.

The 008 and 009 eproms don’t have this variation in ambient air temp trims (they have 3.1%), so I don’t know why it shows up on the SP eproms.  I moved my 851 air temp sensor from the airbox to up behind the LHF indicator, which helped, but didn’t totally eliminate the issue when using an eprom with the SP based ambient air temp trim table.

And, finally, we get to applying all the above.  I had an SP4 in recently which was running a bit odd after a restoration and also stalling.  During the resto it have been found that two of the injectors were dodgy, but they had been replaced with the green IW031 injectors as found on the 1989 on 851 Strada, 907 and 750/900SSie, not the red (IW042).  I supplied another pair of greens to make them all green, and on the injector cleaning company’s test bench the reds flowed 40 (of whatever units) and the greens 65 from memory.  So the greens flow quite a lot more.

I also went through the valve clearances, tightening the closing clearances and reset the cam timing to 98/102 centrelines.

With all the above in mind, I made a revised eprom with changes to the fuel (guessed) and spark mapping and the ambient air temp trims and then ran it on the dyno and road and adjusted the fuelling as required.  The fuel changes weren’t a blanket offset, and there’s definitely less change on the WOT line from 6,500 to 8,000 rpm.  The changes to the fuel mapping are shown below.

 

The changes I made to the spark advance mapping weren’t just dyno power related.  The eproms for the Kit and SP motors have a lot of advance at low rpm and throttle to try to overcome the cam duration, up to 59 degrees at 2,500 rpm and above.  But at idle they drop to 10 degrees, and it’s just not enough.  Generally, the more advance you can run the more stable the idle will be.  I was only able to add 5 degrees without causing the idle to increase markedly.  The issue you run into is that as you increase spark advance you increase idle speed.  You can lower the idle speed again on these P7 ecu bikes by winding out the idle stop, but this does two things: it resets your zero throttle line, changing the fuel mapping at low throttle and also make the idle much dirtier emissions wise for Hydrocarbons and Oxygen.  The long duration A cams make this much worse, so you have to strike a balance.  Once I was done, you could walk up to it cold, hit the start button and it would fire and idle without throttle.  Well, once I’d replaced the rooted starter clutch and fitted some of the Motolectric leads anyway.

 

Another way to improve cold idle is to add advance under the idle rpm.  The SP spark advance map has rpm break points at 1,000 and 1,500 rpm.  If I’d had the time to do all I wanted (i.e., if I was going to get paid for it instead of writing it off) I would have added a 1,200 rpm break.  This way, to have 15 degrees at hot idle, the 1,200 rpm point would be 15 degrees, as would the 1,500 rpm point, giving a nice stable idle.  However, the 1,000 rpm point could have 20 or even 25 degrees advance.  This way, when cold or if the idle drops, it picks up more advance so picks the idle up again without running away with itself above 1,200 rpm when the engine is hot.

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TB1100 and TB1198 back in stock!

Reduced hours over school holidays

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I'll be on reduced hours over the next two weeks due to the school holidays.  You can try my mobile or email me and I will be in the factory for some days.
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Fitting an Acewell dashboard to a Monster ie with immobilisor

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I recently fitted an Acewell 3963 dashboard to an M400ie, in place of the original that had gone rather wacky.  The owner wanted to move away from the original dash, and I had a 3963 in stock that I was planning to fit to my Monster at some point.  So I figured, “how hard could it be?”  Or, as it turned out, "how much money can I throw away?"  A lot, as it turned out.

There are a few issues that need to be explained with this, as it’s not as easy as first might appear.

1.       This is a 2005 M400ie, so it has the immobiliser with red and black keys.  The immobiliser unit itself is inside the dash.  To enable the bike to run with the original dash removed, the ecu has to have the operating file modified to ignore the immobiliser function.  Commonly known as “reflashing”.

2.       The indicator control system is inside the dash.

3.       The inputs, etc, for controlling the indicators and turning idiot lights on/off tend to be earth based.  So to turn a light on, the dash earths the circuit.  Or, in the case of the indicators, the LH handlebar switch itself is just an earth path.  Whereas on previous models (and as most would expect) it’s a 12V path.

4.       The intention was to not cut up the factory wiring, so an original dash could be refitted at some point.  This meant finding the corresponding 26 pin connector to suit.

5.       The connector to plug into the wiring loom, to make it a nice, professional looking install, is available, but only in PCB form, not wiring loom form.  You can get it from RS Online like I did here and the TE Connectivity (who make it) info is here.  I also bought some terminals that actually fit the other side (wiring loom) connector, but they too would be good to use to connect the wires to the dash side connector instead of the ferrules (I'm getting ahead of myself, see below).

I went through the wiring diagram and worked out what went where at the dash connector , shown below.  Red indicates that I didn't use a given pin or couldn't make it work.
 

I had some dash mounts cut (water jet from memory) to a design based a little on a bracket Acewell make, but which is too narrow for the Monster mounting holes.  Then I bent it to mimic the angle of the Acewell part to make the dash readable when sitting on the bike and polished it.

I have 9 more, as the minimum set up cost covered 10 in total.

The wiring proved a little more infuriating, and soaked up a quite extraordinary amount of time, as things do when you’re making it up as you go along.  And re-doing things that didn’t work as planned the first time round.  Etc.

I purchased some little ferrules from Altronic into which I squeezed some solder paste, then slid the ferrule over the connector pin and then slid in the wire to be connected into.  With the white plastic end cut off, the slightly flared end of the metal tube is exposed and is very easy to slide the wire into.  Then hit it with the soldering iron until the paste went shiny and runny.  I found it important to hold the wire in the ferrule, as when the solder went runny it had a tendency to push the wire out a little (or more).

The following series of photos show the product.  Unfortunately, the only photo showing the full wiring junction connector is a bit blurry.  Which is a bit odd of the iPhone.  I must say, the iPhone’s ability to take up close photos of little things is far superior to any camera I’ve ever had.

You can see in this photo the red and black wires that go from the dash connector at the bottom up to the large white connector and then out again to the green or smaller white.  These are the common earths and switched power.  Likewise, the indicator wires (brown) join at the LH (small white) or RH (green) connectors.

At the connector, I slipped heat shrink over the wires before fitting them so I could then insulate them individually.

A salesman at one of the electronics shops had recommended using a two part epoxy to ‘pot’ the back of the connector once finished, but I asked Jack at City Auto Electrics about this and he said he’d just heat shrink it.  That way, it’s not permanently fixed.

The photo below shows the dash connector, with the terminal #’s visible at the ends of the rows.  1 is top LH, 26 bottom RH.

To make the indicators work I had to convert the indicator switch to a power in/out style.  To do this required a few things.

First, I used a motogadget  m-Flash solid state flasher control unit.  This little (and I mean little) unit will supply an on/off/on/off/etc voltage output whenever a load is placed on it.  There are a few other versions of it available I believe, but this was the most obvious one I found.

Power for the m-Flash was taken from the loom side of the ignition switch connector, from one of the wires that receives power with ignition on.  I simply removed the original terminal form the connector, cut off the terminal and replaced it with a new one with the m-Flash input wire added.  It’s just a typical spade terminal with locking tab.  In the photo below, in the centre location, yellow wire is original, larger red m-Flash input.

From the connector the power wire runs through a 10A inline fuse holder and into the m-Flash.  The output wire of the m-Flash I fitted into the loom connector for the LH switch block in place of the wire that originally provided the earth path for the central terminal of the switch, used to earth the flasher circuit activation wire inside the original dash.  This way, power will flow through the switch and into the new dashboard wiring, where it will be sent out 3 ways: idiot, front and rear.

The wire that needs to be removed from the loom connector to the LH switch block (as per the photo below) is the (edit, was previously wrong) second from the bottom wire on the RH side, which is black.  As a reference, the top LH hole doesn't have a wire in it.  In its place (using an AMP weatherpack terminal) goes the m-Flash output wire.

I just heat-shrinked the original wire and zip-tied it out of the way (or maybe poked it up the plastic sheath).  Not important, it’s an earth anyway.

So now we have power from a switched source through an indicator control unit into the LH switch block and out again into the wiring loom going to the dash.  As the wires to each indicator also go through the dash connector, joining the input wire to the two respective indicators (front and rear for each side) completes the power circuit.

Oil pressure was easy, as the Acewell uses the normal downstream earth switch to complete the circuit and turn the light on.

Similarly the Neutral light.  As this is a single wire neutral switch model, it again uses a downstream earth switch to complete the circuit and turn the light on.  On an earlier model with a two wire neutral switch you could earth one side of the switch and connect the other side to the dash to make it work.

Luckily, the tacho worked from the ECU output.  The tacho input in the Acewell was set to 0.5 (signals per revolution I think, meaning 1 signal per cycle).

Unfortunately, that was the end of my luck.  The original speed signal, engine temperature and fuel gauge circuits wouldn’t play.  I’m not sure if the fuel gauge reading was some error on my part, as I don’t understand why it wouldn’t work or if I managed to kill the sensor (not sure how), but I couldn’t make it work.

Edit - I fitted an Acewell to one of my Monsters recently and found the input to the dash for the low fuel light was an earth input, not 12V as I had assumed.  In that instance, I fitted a relay that was switched on by the 12V output of the low fuel sensor, and the relay main circuit (30/87) was an earth circuit that gave a switched earth into the dash input.  I would expect this dash was probably the same, and I just didn't notice the detail in the instructions.  So be aware of input type.

So, for a speedo signal I bent up a small sheet metal bracket and mounted the supplied Acewell sensor just in front of the LHF brake caliper.  This worked rather nicely.  Painted black is was very unobtrusive too, although it makes the photo of it lack detail correspondingly.

My main aim here was to make a mounting that wouldn’t lead to any sort of issue when the front wheel was removed.  It’s just a bracket, with both calliper screws passing through it that sits nicely inside the fork leg and routes the cable easily.  It annoys the hell out of me when I get a bike in and a routine operation becomes a nightmare of undoing some owner backyard bodge that has to be redone.  So I try to make my bodges user friendly.

The magnet was fitted to the front disc through one of the mounting buttons.  I did remove the wheel and re-balance it, as the added weight was maybe 8 grams.

Acewell offer an engine temperature sensor nominally labelled as “Honda compatible”.  It’s just an M10 threaded sensor with a graduated output, which conveniently goes into the same hole in the oil screen plug as the original Ducati sensor.  So out with the old and in with the new.  I think I must have removed the connector (as the next photo shows) so I could heat shrink the wires.  I really hate uncovered wires.  You get good at disassembling connectors when you do a lot of this.

I made up a little loom to run from the switch connector back to the dash, which went around the back of the clutch cover bulge to hide the big arsed white connector.  I guess I could have swapped it for something less obvious (like an AMP Weatherpack 2 pin), but then if a replacement has to be sourced by the owner it wouldn’t be fit and go.  I’ve found a very handy automotive loom manufacturer locally (Retro Looms) who stock all the plastic sheathing, which I like using to give the factory look.  It just hides add on bits and pieces so much better.

To keep the loom where I wanted it, I bent up a small locating bracket from coat hanger wire mounted to a clutch cover screw.  Coat hanger wire is great stuff, and usually zinc plated.

The ECU warning light I ignored.  To run this a relay would need to be fitted that would supply power to the dash circuit that is triggered by the original ECU earthing wire earthing the switching side.  The owner wasn’t fussed, so the time was saved.

All that was left to do at this point was jam the wiring somewhere that it wasn’t so obvious.  The owner elected to do some covering himself, to save paying me to do it, so I positioned all the connectors up in front of the airbox, as below.

And we called it done.