Saturday, July 4, 2026

Airbox / Air inlet mods for Sport Classic and Hyper Motard 2V

 Fixing the Sport Classic and HM airbox restriction the cheap way.

{{digressing}} The expensive way is the StarAce airbox. A customer brought one in a couple of years ago for me to fit to an SC1000, and with the ECU file (well, numbers dumped from a twin shock based file into a single shock file due to the different air temp sensors) I had made up for another bike running the big flat MWR panel airfilter (ever tried washing one of them?), based on one of Tom's Zard with hacked airbox maps, it was surprisingly fast. Equal to anything else I've sampled on one of these bikes for sure. Like "get it into second before you open it all the way or you'll be over" fast. Bringing the wow and yeah baby, and the typical issues pertaining to those lacking resistance to temptation and restraint.

{{getting back to the subject}} The little square hole on the right is all the air entry these bikes have from the factory - it's amazing they can make any power at all, left alone 85 ish.


The big hole at the top and smaller hole through the bottom are the low buck improvements. Love the hole saw. The big hole at the top is the Ducati Performance-esque easy bolt on improvement. The hole in the bottom the "well, we're here, so why not" improvement. Just don't hole saw to far through and into the shit below - it's much more useful in its original condition.


This one had two seized screws and spinning inserts too - the two closest to the filter front and left. While the little 8mm screw heads meant I could very conveniently hold the head while drilling the head off, one wound out happily with the LH drill bit, while the other thread at the front was seized into the insert. With the heat generated the plastic surrounding the insert when soft and it came out the bottom of the airbox moulding. I drilled through the rest of the M5 thread to get it from both ends and gave it the Wurth Boltex treatment. With the insert held securely in the vice, one of the old style (and generally crap) reverse twist easi-outs just wound it out. Happy days! Smothered in araldite and jammed back into the airbox, the insert seemed to hold just fine with a screw back in it. Just don't go too tight.


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Index - of sorts anyway. Think of it as a guide. 05/07/2026

 Bikes 'n' stuff



Camshafts and Valvetrain


Clutch


Electrical

Using an Ignitech TCIP4 on a Ducati ie engine converted to carburettors 


Dyno Runs



Engines 


Inlet tuning

Exhaust


Maintenance


Suspension



Tuning - Carby

Tuning - Fuel Injection


Moto Guzzi


Cagiva


MV Agusta


.
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748 / 916 Replacement fuel pump - pick up extension required when using later style pumps

I see a few pre 1999 model year 748 and 916 with running issues after the fuel pump has been replaced with a non original pump.

I checked the fuel pressure on one recently and it was 2 bar. Testing the pressure regulator showed it was letting go at 3, so it wasn't that. Pulling the pump showed the problem.

I went through this a few years ago and put a couple of videos on Youtube about it - the first in exasperated confusion (that bike had arrived from another shop after someone else had done the pump replacement), the second after I'd worked it out. That bike back then wouldn't pick up fuel at all. I've seen a few since with running issues or "It ran ok for a while, then played up" like this one, with exactly the same cause.


The OEM early 748 and all 916 fuel pump is a Walbro, with a long snout on the pick up side. See the first photo. People replace them with generic pumps that have no snout, as per the second photo. If you do that, you need to add the pick up extension piece to lower the fuel pick up level to just above the screen. And cut a little slot in the pump rubber to let the plastic bump stick out. The screen provides enough restriction to stop the pump sucking without it. Pick up extension: 48410291B, retaining clip 85040311A. These parts are from the parts catalogues of 1999 onward models - 996, 998, ST2/3/4, etc.







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Marelli 5AM "bad software" issue

This may be one of those instances of me making something up to try to explain something I've experienced.

I have a customer who used to have a late 999S with a Termi full system - one of those with the hydroformed section around the later style black swingarm.  I serviced it a few times, and one thing that I noticed (but never really thought about too much) was that, after I'd run it on the bench to do the tune and check the thermo fan, then shut it off, checked the chain tension, headlight aim, etc and pushed it outside to go for a ride, it would idle funny once restarted half hot - in the region of 50 - 60 degrees on the dash.

An erratic idle you could hear and feel.  But during and after the road test, it'd be fine.  Just like it had been on the bench after being started from cold.  As such, I never really paid too much attention to it.

Then, some time later, I had a very late 2005 or 2006 model year 749 come in with a weird running issue.  It would intermittantly run badly at low speed, idle badly, cut out at idle, that sort of thing.  It was fine as an all std bike, with the problem starting after a Ducati Performance slip on kit with ECU was fitted at a local dealer.  It had been back to them a few times, with no improvement, and had even had a custom ECU remap - again, with no improvement.

While I was going through it all, trying to find something wrong, at one point I restarted it half hot and noted an erratic idle and thought "have I seen this before?"  So I hooked it up to the diagnostic tool to see if there was any weirdness going on, and lo and behold - there was.

Everything was as expected while it sat there sounding odd, except that the ignition advance as displayed was all over the place.  From memory, if I was expecting 12 degrees, it was showing 4 to 14 sort of thing and varying rapidly.  Just like it sounded.

Then, at some point, which I later detirmined had no relevance to the engine temp, or how long it'd been running, or how long it'd been since the ignition was turned on even, it would suddenly smooth out.  Like just clicking your fingers and it was beautiful.  And, most importantly from my point of view, the ignition advance became completely stable, with no variation displayed at all.  I ran through the scenario several times, and every time it was the same thing.

The problem then was - why?  And how to fix it?  First I had a look at the ECU fitted - DP # 96513904B, Marelli software # 2218PT70.  

Interestingly, the part # 96513904B is listed by Ducati as fitting both 2005 - 2006 749 and 2004 - 2006 749S.  Which is, of course, nonsense.  The 749S has the 6mm valve stems with tapered collets, bigger valves and most importantly, a lot more camshaft duration.  But that's the only 749 5AM DP slip on kit ECU I've found.

Anyway, ECU fitment lunacy aside, none of that really helped.  The owner had provided the original ECU, so I read the file out of that and it was Ducati # 28640851M, Marelli software # 2219DS32.  Having a look through my 749 5AM files I found I had 28640851G / 2218DS27 as well.  Which begged the question, why did they stop with the G and go the M?

Comparing the 96513904B and 28640851G, they appeared to be much the same basic software and locations wise.  Whereas the 28640851M had variations, in the typical Ducati / Marelli fashion, where everything is just in a slightly different place.  So it was somewhat different at least.  I had another 2005 MY 749 in recently and it had the 28640851G ECU originally.

Because the fitted DP ECU had had a custom map done as well, I copied the fuel tables, etc, from that ECU and dropped them over the original 28640851M file to make a "not bad" basis, as well as played with the ignition advance, advance at idle and other stuff like I usually do.  I flashed that in and set it up, and it was happy again.

So, I'm curious to know if anyone else has experienced this specific scenario.  I'm not asking for everyone who has a badly set up 749 or 999 to pipe in, because I know there's thousands of them out there.  But if you've noticed an erratic idle on half hot restart that settles noticeably after some time, I'd be curious to know the specifics - model, year, ECU #.



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Chain and sprocket replacement on a 996 - with a difference

I had a 996 in for a major service, and chain and sprocket replacement was one of the required add on jobs. With a difference, as it turned out. The rear sprocket was a flat aluminium piece bolted directly to the sprocket carrier. Not something I had a source for, although I do have some suspicion of where it came from.



As to why it was that way, the ring with holes bolted to the front of  the hub would indicate that a cush drive bush outer sleeve had some out and taken off the hub face. Something that was a bit unusual by the time 996 came along. In my experience they tended to chew out the circlip groove, allowing the sprocket to wander into the hub. I figure this fix was either a knee jerk reaction or final solution style approach - removing the failure point all together. Either way, not important - I just had to deal with what I was looking at.

I talked to the owner, giving him the option of going back to std arrangement which meant buying 5 cush drives ($250) and a rear sprocket (starting @ $220) plus a circlip, spacer, etc. Or sticking with something like it was, as that'd be a lot cheaper even with spending some time making it work.

I emailed Melissa at Metalgear, who is an absolute font of info when it comes to brake discs or sprockets, asking if she had any 525 rear sprockets with 5 mounting bolts at 110mm PCD. She came back with a couple of options, mostly being Africa Twin. I figured that was good enough, with good availability going forward, and chose a 42 tooth part with what I figured would be the best visual result.

The two main issues were the centre diameter - 55mm on the Ducati carrier, 80mm on the Africa Twin sprocket and the 12.5mm bolt holes in the sprocket vs 10mm in the carrier. And a third being it seemed to me that the sprocket needed to be spaced in from the carrier. I had a couple of OEM style 916 kicking around, and on them the sprocket appeared to be 2.5mm off the carrier as best i could measure. Using the laser aligner on the rear sprocket and pointing at the front confirmed that.

I scrounged around for something to make a centre spacer out of, finally realising the only piece of aluminium I had big enough was the original sprocket. With the added bonus that the centre diameter was already exactly the right size. At that point I found it was 520, not 525, but that only meant it was 6mm thick instead of 7mm, not overly important. I cut the centre out and left a little lip to retain the spacer behind the sprocket between it and the carrier. The lip was possible due to spacing the sprocket off the carrier.




The spacing and 12.5 to 10mm hole reduction was achieved with the same part - five little top hat spacers fitting into the 12.5mm sprocket holes and captive between sprocket and carrier. I had some 20mm steel rod and a new carbide tip parting tool to use, and they came up quite nice. I do enjoy machining things.





Five M10 bolts and it was done. In the end, the centre spacer was a bit redundant - the five bolts went in so tight and clearly centred that you could rotate the spacer between carrier and sprocket. But I felt better for having it there anyway.






Once the chain was on and I could run the laser along the chain path I figured that maybe 2.25mm, or even 2mm spacing would be enough. Variation in chain tension with rotation was well within the typical.

On the road test I didn't notice anything I would think was lack of cush drive induced.  Not that that necessarily means it’s a good idea.

 

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Low voltage at ignition units and coils - Carb model SS and Monster

I had a carby 900SS in that was hard to start and could run funny at times. Although it clearly had carb issues, based on another 900SS I had recently with similar-ish issues - FCR carbed big bore engine that was hard to get to fire after sitting for a while - I checked the voltage at the coils / ignition units with the ignition on and not running. It was 9.3V, which was 2.5V less than at the battery.

To fix this, I fitted a relay triggered by the original power supply wire and modified the little loom to run power from the relay and earth it all back to the battery directly. Seemed pretty happy after that (then I got into the carbs to fix them too).

Photos show the install. In this case, CA Cycleworks Exactfit 2VCOILS had previously been fitted (not by me), and they're upside down to how I'd normally do it. But it did mean the relay fitted in there very nicely indeed.



Given these carby models are now all at least 25 years old, it's something worth checking.
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