VM32s 340 Invader

[john.0_o]

I have installed two new VM32 carbs and am having some problems,as I expected I would.
The carbs are set up with the factory suggested jetting and 3.0 slide cutaway.
The engine seems to run great above idle but I'm having a problem with the pilot circuit,I think.
I can get a high idle with the idle screws nearly all the way in and the air screws seated.
Is this telling me the current pilot jets are grossly undersized.

[jimvw57]

Are these brand new, used and rebuilt?

It is possible that the needles could have been tightened down at one time and damaged the seats in the carbs. Not too uncommon. The factory setting is just a starting point. you may need to go in or out depending on local variables.
With the air screws all the way in, you are restricting the airflow or enrichening the mixture.  Sounds like an air leak somewhere, like a carb mount or a seal, possibly a primer.

Are both slides close to the same openings?

[john.0_o]

Hi Jim
Carbs are brand new and the air screws have never been tightened down as far as I know and slides are in sync.
Chokes had lots of slack so shouldn't be leaking and primer nipples are connected to each other.
The engine reacts the same when the same adjustment is made on either carb,so I don't think there are any leaks unless the same on both sides.
Nothing has changed or been removed intake wise other then the carbs and I had no air leaking before,but I will look further into that tomorrow.

It feels like if I could turn the air screws in another turn or two that I would be able to back out the idle screws.

The bell on the new carbs is 58mm in diameter (about 10mm larger than the oem) and longer with more of a taper,maybe effecting air velocities or something??

[Checkmarks]

John,

Open the carburetors and put in the next higher sized pilot jet.  The second thing I would look at is the cut out on the throttle valve.  You say this new one is marked 3.0.  What I do know is the 440 has a 2.5 cut out throttle valve, unsure on the 340 motors. 

What I can share is the 3.0 throttle valve will cause you to run lean in the mid-throttle if your motor needs the 2.5 valve.  This feature in Mikuni's affect the off idle and into the mid-throttle.  All that matters is what the piston wash looks like after running and before holes melt through pistons.

[john.0_o]

Checkmarks

Cutout is whats in the books and what was in the old carbs.I haven't done anything with the pilot jets yet because I discovered the bypass holes on the new carbs are smaller then the ones on the oem carbs,the pilot outlet holes look about the same.The specs are in the manual for these holes,should I drill them out,or would just adjusting the pilot jets be sufficient.I don't want to ruin these new carbs but at the same time I don't want to damage the engine either.

[Checkmarks]

John,

Another thought.  Have you changed your seals lately?  Idle problems are symptomatic to bad seals.

No need to drill out any holes.  I am certain Mr. Mikiuni knew what he was doing when they made the holes a touch smaller.

You must learn if the motor is not idling from a lean condition or rich.  Have you tried opening the choke and trying to get to reasonable idle?  One fouled plug could also force you to 'turn up' the idle.  Feel the manifold and check if one side is cooler than the other when you first start up and get to the high idle.

[john.0_o]

Checkmarks

Seals are relatively new with hardly any miles on them.

I figured the OEM carbs are designed to Kawasaki specs and thats why the holes are bigger.

Opening the choke a bit would bring it back to life when it was fading out,it would shortly fade again after closing it.That was before I had the air screws all the way closed.
With the air screws closed and idle screws almost in all the way it idles a little high but good.Both sides of the manifold seem to be the same temp.

I'll go ahead and attach the tach and put in some bigger jets today and see if anything changes and report back.

[jimvw57]

 Just a note: I got a sled a few years ago that was supposedly a rebuilt motor, new seals, etc that didn't run great but did run. After messing with it for almost a year, I cracked the case and found the crank seals to be torn and 1.2 missing from being installed on a dry crankshaft (I'd guess)  so unless you know how good a job someone did or did them yourself,  crankseals, crankseals, crankseals....

I spent a lot of time on carbs, and ignition thinking it was the problem when it was those pesky seals.  (just don't want someone else to have the same aggravation  I did)

[john.0_o]

I installed #30 jets and it is idling smooth at 3500 now,just need to dial them in with the sync tool.
I still feel like the idle screws are in a bit far,that could be because of the high idle speed and/or me thinking to much.

Jim

Seals were installed by me and were packed with grease.I had the gear case cover off to put in a NOS oil pump and the outer seal was still packed with grease,so I would imagine the crank seals are in a similar condition.Great advice though and thanks for it.

[jimvw57]

3500 might be a bit high but as long as the sled doesn't move at idle, run it!!