I'm just fooling around with carb sizes to have something to do over here.

Once I open up the intake port entry a little, or at least just bevel the leading edge all the way round to match the larger intake manifold, then the 40mm might be able to shine a bit more.


I could just throw the 331 on it and be done with the entire thing quickly but I want to stretch the mod variations out over time.

 

If Mikuni would have offered a 38 pumper I'd probably have gotten that instead of the 40.

Looking over the 40mm carb's basic design, I think it'd be possible to sleeve it down to 38mm if I ever gave up on it in its current size.

 

Can't you convince the school you're at that they need an a/f meter for the auto mech dept?



(smilies aren't working btw)

 

]I've already adjusted my nozzle to shoot mostly to the left of the needle, giving it a more direct port shot, and will see how it reacts on the next ride.


Oops


Edit: Hmm not so fast with that adjustment to miss hitting the needle...there's a lot of talk online about the dreaded FCR bog, with various way to attempt to fix it. Maybe that straight shot into the port is too much?

I guess I'll go back to bouncing mine off the needle jet



I do find that I have to run the AP timing screw (blue arrow) completely all the way in to delay the AP shot enough that it doesn't hit the slide.



If I can't find a longer 3mm x .5 screw I'll chop just a little off the top of plunger rod (red arrow) which will allow me to delay the AP's shot of gas to after the slide is out of the way more easily with that adjustment screw.

 

Really hard to do since it is a middle school with 11-14 yr olds... 8^D

The career center is county wide and a separate entity, no chance to do that sort of thing.

 

This whole accelerator pump thing really makes me wonder just how well the plain flat slide would work, considering they used the old round slide for decades on XRs, SRs, XTs, TTs, and four strokes from 50-650. If my old SR was reving around 3500 I could pretty much crank it full throttle without a stumble. The only time it really stumbled was when it was below the useable power range. It seems the smaller the engine the less that thumper "gulp" issue would be of issue.

What range of throttle movement does the AP operate? If one is working mid throttle will having the pump really matter?

I seriously think I'm going to start watching ebay for a dirt cheap flat slide and play. I can always use it on my SR...

 

The AP on the 36 was at one point adjusted to kick in late, almost like secondaries on a 4bbl carb. It took as much throttle as I wanted to give it without hesitation until the AP kicked in-but some of that could depend on your gearing.

Mikuni says to set it to kick off at 3/4 throttle via the black allen screw you see sticking out of the lid.

How a bike would do at mid throttle depends how hard you're cranking it at mid throttle as the AP only responds to fast motion if there's a leak jet. I don't think there's a leak jet in the Mikuni but there could be some sort of bypass to allow for easy throttle movement not engaging the AP.

A regular flat slide may not bolt up as easily if it's dimensions are much different.

 

You gave me a few links in another thread. Some digging shows the dims are

36-2 intake 43 length 100 height 170 bell mouth 62
36-68 intake 42 length 100 height 176 bell mouth 54

So it would take some heat (maybe hot water to get it to stretch) to open the air boot that much if needed. The intake shouldn't be an issue.

I'm going to keep an eye out on ebay. There was some bizarre unit for $39, but the modifications and lack of information is a bit scary. Another kind of whipped one was on at $50. It will just take a bit of time for one to show up at a price worth risking on the experiment.

 

That plunger rod the red arrow is pointing at above just pulls right up and out. I already shortened the 36mm's rod 1-2mm since it's sitting here on the bench.

 

I ran the CVK 34 over my test course for the first time. It registered a 5.38 sprint starting from a 17kph roll; not as far behind the 36mm carb's previous 5.12 as I would have guessed it'd be.

A nice power wheelie on the shift into 2nd, not quite high enough that I had to back out of it - but almost.

Showing again I think the limitations of the intake tract somewhere along the line without some port or valve work. I'd bet the 33/34 smooth bore would produce a time much closer to the 36s best effort; if not equaling it.

Maybe it's as simple as you can't bolt a bigger carb onto the stock sized intake manifold (and the flange hole behind it) and expect a miracle?


Time to do the MCM next !