Sunday, March 5, 2017

More Minnie the 400 Monster dyno runs

I took Minnie to the dyno today to see how the 2-1 works.  Not well as it happens - red is the 2-1 curve, blue the previous session with the std headers and Megacycle mufflers.

Pretty much dyno'd how it feels on the road - goes well under 8, no point going over.  I was going to set up one of the previously dyno'd Megacycle muflers to give just the change due to the 2-1 header, but didn't get to it.  I hadn’t revved it hard before the 2-1 went on.  Now that I have a tacho fitted to know how hard I am revving it, I can see that it would have been very unlikely that I was going over 8 anyway.  As such, I really didn't notice the now crap (ish) top end in comparison to the previous set up.  Maybe I need to make a twin muffler mounting bracket for under the tail and cut down the second Danmoto muffler to fit with original header.

I don't have any air/fuel for the original exhaust and Megacycle mufflers, as the bike killed the dyno on those trips.  The rpm and air/fuel were shutting down when we tried to run it.  After the last session I fitted resistor spark plugs, which you need to run with the Ignitech and which all these carby SS bikes (should have) had oem.  I assume that’s what made the dyno control happy.

First runs were baffle in and then baffle out.  I modified one of the Danmoto baffles I had.  It has 12 holes around it, and the total area of the holes was about the same as the muffler internal diameter anyway.  I machined the end cap of the muffler just a little to allow the baffle to slide in, and them machined a circlip groove to hold it in.  Of course, I didn’t have any circlips big enough to start with, so I bent up a round clip from coat hanger wire.  Gotta love coat hanger wire.  As below – without, machining, and with.

Made so little difference you’d have to call it none.  Then I found that the Showa fork spring preload tubes are a perfect fit over the Danmoto baffle, so I slid a tube over, tacked it on then cut off the original end cap.  The internal diameter of the baffle exit is now probably a bit under 20mm.  Again, not a lot of difference, but I ran with it. 

You can hear the slight change in these clips I took in the dyno room.  Not great sound, but definitely quieter with baffle from the bottom.

As expected, it hurt the bottom end a little.  Not as much as I’d hurt the top end though.  Baffling the mufflers usually effects the peak torque more than the peak power, but in this instance that’s a bit hard to see.

It was a bit (fair bit) on the rich side, so I thought I'd try it out without the airbox lid.

It was a bit better power wise, but the mixture change was pretty extreme.  More than I think I've seen before on a 2v motor.  Too rich to more too lean.

Then I tried it with lid, but without the snorkels.  That helped a bit, but still too lean on the needle.

I have some of the original 400ss carb springs, that are a lot lighter than every other OEM Mikuni spring I’ve seen them fitted with.  I might try them, not sure if that'll make it better due to the increased slide opening lifting the needle more, or worse because it'll have less vacuum over the jet and the needles aren't tapered enough anyway.  I do have some jet kit needles that might be the go.  Probably with springs as well - you’d just call that fitting a jet kit.
I rode it back from the dyno with one snorkel fitted and without the baffle.  It felt a bit stronger without it, but the missing snorkel may also have been helping there.

The Ignitech unit I fitted before this dyno session has the same advance as the std boxes.  Well (you know when you make assumptions and then later you think "oh"), maybe I should check that - it should have the same advance.  
I know that from the previous 750 engine testing that lack of advance hurts the top end and can give an exaggerated choppiness to the curve.

This early Ignitech TCIP4 has a delay that increases as rpm climbs.  The newer units (this one I've had since 2005 or so) don't.  I thought I had allowed for it in my curve, but maybe not enough.  I did have the oem boxes with me at the dyno, but my time was pretty much up there and I had to get back to work anyway so I didn't.  One thing I hate about not having my own dyno running is not being able to act on all the things you think of later when it's too late.

So maybe it didn't have enough top end advance, and it was rich anyway.  
Fairly extreme fuelling (well, air entry affecting fuelling) changes didn't make a big difference either, although it did go from too rich to too lean.  The last run I did had the mixture back at 13.5 or so in the crap top end area, so that pretty much rules mixture out.

Although I ran these same carbs years ago when it was a std 600, and I would have thought with a smaller engine it should be leaner due to less suck.  For some of the production years the M400 and M600 are fitted with the same carb spec (same part number).  I did shoot some video through the airbox lid without an air filter fitted of the slide, and it did look like it was lifting all the way up.  I was wondering if it would, given it's a pretty big carb for a 400.  Lots of fuel flying around too.

Through the snorkel hole

As it sits at work now (waiting for a nice day and time to go for a ride, it's pretty hot here now) it has one of the Megacycle mufflers fitted to rule that change out, and I'll put some oem ignition units in my pocket and fit them on the road. I really can't see the exhaust alone hurting it this much, as nothing I've done exhaust wise in the past has, but I'm often wrong.  And I do have concerns that the 2-1 merge isn't deep enough into the V of the original connector.  It may actually allow flow from one cylinder to go back up the pipe toward the other cylinder. Not so bad from the vertical as the pipe in is angled, but from the horizontal it can.  That's possibly an issue and not one I can do a lot about with this header set, especially now they’re ceramic coated.

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