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Old 1 Week Ago
Austin84xlx Austin84xlx is offline
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Question Mikuni VM 38-9 on 1984(late) XLX 1000

I have put a mikuni roundslide in my 84 sporty, it does have bigger cams, with a longer duration and straight pipes. I am still stuck on getting idle mixture right. I have gone down multiple times from the stock pilot jet. a started with the 30. It idled best when the air mixture was turned all the way out. So i figured I needed a smaller pilot. I had the same happen 3 more times, and I'm down to a 17.5. It starts fine, but I'm still coming almost all the way out with the air adjuster. Did I mess something up? Why is my pilot so much small than what all the forum post say. I'm going to try with the 15 tomorrow. It currently starts without even using the enricher, it actually bogs down if I use it. I might also try a 32.5 to see my intuitions were backwards.
It was running fine with the stock carb, but i hate dealing with the stock carbs issues that just pop up, all the time, and I've read the mikuni is quite amazing.
Everything is stock vm38-9 except the pilot jet.
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Float level too high?
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Originally Posted by ryder rick View Post
Float level too high?
I didn't really actually think about that, I adjusted it down already because when it first was on, it leaked out the overflow, but it might be to high still.
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i started over from 30, I made the float adjustment, it was about 24mm from top of gasket, still seams a bit rich, but i get a little spit here and there at idle after warming up.
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down load the vm tuning manual
it does not operate like some carbs, aka fuel vs air control.
also, it is very important not to have the slide open too much as it messes with things like the enrichen circuit.
start with the suggested setup. it can easily handle high performance mod's.
http://www.mikuni.com/pdf/vmmanual.pdf
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Quote:
Originally Posted by bustert View Post
down load the vm tuning manual
it does not operate like some carbs, aka fuel vs air control.
also, it is very important not to have the slide open too much as it messes with things like the enrichen circuit.
start with the suggested setup. it can easily handle high performance mod's.
http://www.mikuni.com/pdf/vmmanual.pdf
It starts( enriched for 30 sec, then turn of enrich), it runs great while riding, I can't get the idle right in terms of mixture, I went down 1 pilot to 27.5 and i still smell gas in the exhaust and max out my air mixture, Is it because it has 0.5 air jet? i see some say it should have it, others says 2.0.
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Your open pipe is causing reversion at idle, and the pulse draws fuel from the pilot circuit in both directions = rich.
You're going the right way, but I can't tell you what size.
I had this problem with the HS40 on my 1200 Evo, made an anti-reversion cone for the pipes, which helped a lot without the top end loss of a baffle. Jerry Branch sent me a drawing of the cone dimensions, the pointy end is very small.
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Quote:
Originally Posted by kitabel View Post
Your open pipe is causing reversion at idle, and the pulse draws fuel from the pilot circuit in both directions = rich.
You're going the right way, but I can't tell you what size.
I had this problem with the HS40 on my 1200 Evo, made an anti-reversion cone for the pipes, which helped a lot without the top end loss of a baffle. Jerry Branch sent me a drawing of the cone dimensions, the pointy end is very small.
I think i got her dialed in, at least in the low. I'd like a lower idles, but that's when it starts acting funny (below 800). So i'll keep her around 850 - 900. I ended up with a 22.5 pilot, and she alright with it, and i was actually having something happen when i messed with the mixture both ways. ended up 2 turns out or so.that's where it ran most comfortably so to speak. Ill look into the anti reversion cone.
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Originally Posted by Austin84xlx View Post
... i'll keep her around 850 - 900...
That idle speed is way too low. Aim for 1000 RPM. minimum 950 RPM.
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Default I figured it all out

I was an idiot. I didn't even realize i didn't hook the VOES that the bike had to a vacuum, i hooked it to vent. I went and tapped a small barbed fitting on the manifold side of the carb, hooked to the voes, and everything is now right.

Thank you guys for the attempted help, sorry to have wasted your time.
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