VM30 tuning...

Finally got the new jets in the mail. ;D

So my set up now is...
Pilot is #15
1/2 screw out on air mixture, was at 1 but when turned in it idled a bit higher so I must be a bit lean on the pilot.
P-5 needle jet, was a Q2
6F5 jet needle middle clip, was a 6F4 on top clip
145 main jet
Fresh plugs...So I started it up, idled at 4500rpm, let it warm up for 5 minutes, took it for a ten minute ride. Pulled the plugs and I'm running lean(fricking finally, so tired of it being so rich).
So I adjusted the idle down to, 1500, with the air screw being at 1/2 turn, didn't want to go all the way in, I didn't adjust the air screw.

Two things happening, otherwise it is running very smooth.
-When rolling throttle from idle to 1/4 throttle, goes great, when I pull the throttle fast from idle to 1/4-1/2 throttle it cuts out hard.
-When I'm cruising and I go to WOT it cuts out hard.
So I'm thinking I need to go bigger on the main, and bigger on the pilot jet??? The only reason I'm assuming those two things is because the plug was somewhat white when I pulled it out after a ride.
If anybody could give me an idea on my assumption on changing the pilot and the main, that'd be great, if I can avoid tearing the carb apart for the 20th time that'd be great, although I think I've got it down to about 10 minutes now.

Now you're getting somewhere! I would go up on the pilot jet first. Don't try to start tuning the 1/4-1/2 throttle just yet, because any change to the pilot will have an affect on the entire system. Same thing on WOT; wait until your pilot is where it needs to be before changing main jets.

In regards to snapping the throttle open and the engine stumbling, you can't do it with these carbs like you can on a CV type. With a CV carb, you can open the throttle all the way, but the slide won't lift until the engine is ready for it. With these Mikunis, the slide is directly linked to your wrist so too much of a snap and the bike will stumble.

Keep up the good work and remember, one thing at a time!

Thanks! It feels good to be able to drive the bike to work finally, it's a short slow ride through town. Once again, I was going to change the main and the pilot at the same time, rookie mistake, I'll up the pilot to 17.5 and see what I get.

I'm wondering if a lean situation would make the bike super cold blooded? After it's cooled down, it starts very slow and idles very low, after a good warm up, 10 minutes or so, it gets a lot better, idle jumps to like 2500. Is this an indication of being lean? The reason I'm wondering is I don't think I want to change the pilot to richer yet, after it's good and warm it runs so well, and the plugs are looking pretty good, but if a lean situation causes the cold bloodeness I'll definitely give it a try, or do I look elsewhere, or maybe that's what these older bikes are like? Any ideas?

Sounds like you're lean and you possibly have an air leak.

Ohh, so it could be so cold blooded because I have an air leak?

I was thinking the high idle issue would be the air leak, the cold blooded thing would be due to running a little lean.

Though an air leak can cause you to run lean, so could be the same issue, yeah.

Thanks, I'll change the pilot and see what I get. I had to put new carb boots on because the other ones were shot, but they didn't fit perfect and only gave me about an 1/8 inch cover on the bottom side of the boot. I used some high temp sealant, but it's something to keep an eye on. Thanks!

Re: Re: VM30 tuning...

thovda said:

Thanks, I'll change the pilot and see what I get. I had to put new carb boots on because the other ones were shot, but they didn't fit perfect and only gave me about an 1/8 inch cover on the bottom side of the boot. I used some high temp sealant, but it's something to keep an eye on. Thanks!

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I think you're getting to the root of an issue here. I wouldn't trust that this is sealing correctly at all. And the needle jet still seems huge to me. I am running an over bored cb360 with vm30s. It's somewhere in the 410cc range and I'm at a P0 needle jet and it's still a tad rich. I know they're different bikes, but displacement is displacement. I would keep an eye out for a set of intake manifolds that fit well first and foremost. 18" of seat is going to perpetually cause you problems considering that you need somewhere in the neighborhood of 1" just by the stock Mikuni spigot.

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Kiley, you still running the 159 series or did you swap over to the 176?

Re: Re: VM30 tuning...

Sonreir said:

Kiley, you still running the 159 series or did you swap over to the 176?

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Still running the 159 series. They work great, so never needed to change to emulsions. Little rich on idle, but spot on above. Not foul rich, just a little smokey rich. Down the needle or PJ and it's too lean.

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OK... not sure if the OP is running the 159 or the 176, but if the switch was made to 176, somewhere between a P5 and a P8 should be correct. The bleed type needle jets run leaner than the primary types.

I'm running the 159 series. I'm in the middle with the clip so I could lean that out still.

So I just had a chance to check a few things, I checked the plugs when I got home, and was surpised to see they were a bit sooty, I took about an hour ride last night in the dark and didn't have a chance to check the plugs when I got back.
The first check I did when I get the new jets after a half hour ride and the tips were a bit white. So I cranked the mixture out a half turn.
I started it and let it idle for about ten minutes, my idle was all over the place. I tested the carb boots with WD, nothing changed, so I took of the carb boots off and I'm pretty sure I'm having some leaking where they butt the motor. They've been hot enough now that the rubber has softened, and the screws were none too tight when I took them off. I think it started leaking lately because I've been driving it more, more heat, and they've starting leaking.
I'm enlarging the hole on the boot to get more of it to cover the intake part of the motor better, hopefully I can get them to seal. Any ideas if I should use any kind of sealant there to help out, or just tighten the screws good?

I use a bit of RTV between the manifolds and the head and a light coating of axle grease along the inside of the manifolds where the carbs slip in.

The grease helps plug any small air leaks and also helps to keep the manifold from "bunching up" when being compressed around the carbs.

+1. I prefer to use Vaseline on bike parts rather than axle grease. It's cleaner.

Do not overtighten the manifolds. They bow and leak.

176 series are much better on a 4 stroke and start with smaller air jets - say 0.5-0.9mm

Re: Re: VM30 tuning...

Kanticoy said:

I think you're getting to the root of an issue here. I wouldn't trust that this is sealing correctly at all. And the needle jet still seems huge to me. I am running an over bored cb360 with vm30s. It's somewhere in the 410cc range and I'm at a P0 needle jet and it's still a tad rich. I know they're different bikes, but displacement is displacement. I would keep an eye out for a set of intake manifolds that fit well first and foremost. 18" of seat is going to perpetually cause you problems considering that you need somewhere in the neighborhood of 1" just by the stock Mikuni spigot.

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Click to expand...

Ya but, this is a Kawasakiiii, not a Honda, displacement or not... ;D

Kanticoy,
Would you ever share the settings you have in your carbs, pilot, main, etc...?
I think the hard starting has to do with the plugs being more sooted up than I thought and weren't firing the best.
I cleaned up the manifolds and fixed the air leak, thanks for the tips on doing that fellas.
I'm debating on changing to a smaller 159 series or changing it up to the 176 series, but where to start if head in to the 176? Interesting that the 176 is for the 4 stroke but alot of 4 strokers are jetting with the 159 series. Also, most of my driving will be around 30-40 mph, and it sounds like the 176 works better in those ranges, where the 159 may work better at the higher throttle ranges.
Also, I'm in the middle clip on the 6F5 needle, so I'm going to lean that up a clip and see what I get.

A 176 mixes air with fuel in the jet so it comes out as an emulsion with smaller droplets which is what a 4 stroke needs. It is possible to jet correctly with a Primary type nozzle/needle jet/emulsion tube, but there will always be wasted unburned fuel in the exhaust. The trick is to get the fuel that does burn to be in the right proportion to air.

The other difference between Primary (aka 2 stroke) and Bleed (aka 4 stroke) nozzles is that they flow differently and one is richer at the top end than the other for the same jet size. They have a different fuel slope as it's called. Two strokes like to be a little rich at the top end to keep them cool and on a 4 stroke that just makes them run rich at high revs.

The other issue is that VM series carbs are often rich on one circuit and change to lean on another and you have to differentiate between the different circuits. Around the hood, you are running on pilot circuit, slide cutaway needle jet and needle root diameter. The main jet is not playing until almost 3/4 throttle that most of us rarely see.

Mark your throttle with tape at 1/8, 1/4 etc and grab a copy of the Mikuni VM Tuning manual and work out where the problem lies.

Good info teazer, I've got the manual and was playing with a few things today. Something pretty interesting happened...
So i got home for lunch and pulled out the jet needle and leaned the clip out, I have a hunch the midrange is sooting the plugs, since I've ruled out it's the idle, and I haven't been riding at upper throttle range yet.
I left the somewhat sooty plugs in it and was going to go warm it up and start with the fresh plugs after I warmed it up. Got about halfway down the driveway and it died. So I started it up, idle about 1200, and holy shit it jumped to 9000 rpm! Shut it off, started it and it did it again! Walked it back to the garage, started it with the fresh plugs, idle was good and it didn't jump, but I noticed the right manifold was kind of chugging a bit. So I took it off and have made sure it fit good and resealed it with RTV. It's drying now, but I'm hoping the leak in that manifold is what caused the crazy jump in RPM.

So The High Rpm Was A Stuck Throttle Cable, Dicking With The Carbs Too Much I Suppose. Got A Twenty Minute Ride In, A Mixture Of Throttle Positions, Plugs Were A Tad On The Lean Side, But I Can Work With That. Thanks For All The Help Tonners.