Very Difficult Question About Mikuni VM29 Carbs

I need to try the exact same test with the air jets and main jets installed and see how the flow ultimately exits the main jet compared to the others. That seems like the easiest and best test right now...will let you know!

The accelerator pump option is interesting...I didn't notice anything different on that carb but will check again.

I have a #3 carb body lined up if necessary....hoping I won't need it.

79MKII wrote:
I believe the air would be "sucked" through that passage and would mix in with the main jet flow, so it seems like it could have an affect on the quantity of fuel and or air or maybe just the type of stream flowing. If it's extremely diffused and not a proper stream, would that affect performance. This is deep stuff here!

The air passage is a BLEED to the needle jet and it DOES affect the fuel mixture.
Like putting a hole in a straw
The bigger the hole the less fuel will be drawn from the float chamber.
So a restriction will RICHEN the mix and a larger hole will WEAKEN it .
You need to look at that cylinders spark plug to determine if it is running excessively weak or rich.

Sounds like it was drilled like that at the factory. As long as the air jets are the same and the emulsion tubes are too, you should be fine. There are brass balls blocking the drilled passages from the factory. Have they been tampered with?
Steve

It looks like the spherical brass plugs are unmodified.

I tried the same fluid test with the air jets and the main jets installed and the output looks about the same for all cylinders. I'm thinking that the passage might not affect the airflow since the air jet is upstream of it, and will ultimately limit the quantity of air entering the passage. The air jet creates the "stream" of fluid instead of the opening at the inner end of the passage. It's aleady in a "stream" when it reaches the end of the passage. Hope that makes sense. :S

I noticed another issue that might be causing the "stuttering" I'm having at WOT. The mechanisms for two of the slides have some serious slop in them. I can move the slide up and down on those two bores quite a bit. That could cause some chatter, couldn't it? I found some worn and broken parts that I've fixed, so the slides are all solid now. I hope to try these carbs on the motorcycle again soon.

Thanks for all the input!

The air jet does two things, it limits the amount of air that can enter the main circuit plus ,it meters how much air will be mixed with the fuel throughout the RPM range. The vacuume created by the cylinders is what draws the air/fuel into the bores. (atomization) The throttle valve cutaway limits when the main circuit stepps in and the needle limits how much is allowed at any given throttle position. The emulsion tubes do the mixing and can be changed to make it richer or leaner. The nozzle does this too but it's the tubes that make the fine adjustments to air/fuel. The moron that had my carbs before drilled extra holes in the "mixers". Not only was it all on or all off, it would run hot and ping if I didn't stay on the throttle. I had to undo everything he did.
Steve
kzrider.com/forum/3-carburetor/601369-mikuni-vm-33-carbs

swest wrote: The air jet does two things, it limits the amount of air that can enter the main circuit plus ,it meters how much air will be mixed with the fuel throughout the RPM range. The vacuume created by the cylinders is what draws the air/fuel into the bores. (atomization) The throttle valve cutaway limits when the main circuit stepps in and the needle limits how much is allowed at any given throttle position. The emulsion tubes do the mixing and can be changed to make it richer or leaner. The nozzle does this too but it's the tubes that make the fine adjustments to air/fuel. The moron that had my carbs before drilled extra holes in the "mixers". Not only was it all on or all off, it would run hot and ping if I didn't stay on the throttle. I had to undo everything he did.
Steve
kzrider.com/forum/3-carburetor/601369-mikuni-vm-33-carbs

Man, you're having as much fun with your 33's as I am with my 29's! I feel for ya....

Yeah and the slides are 2.0 cutaway where they should be 1.5's. Leaner. The air screws were monkeyed with so I had to buy them too. These are considered Race carbs. Difficult to get right if even.
Steve

Well, I got the 29's back on and this KZ1000 runs better than it ever has! Finally got this messed up set of carbs dialed in. Really ran well through the entire RPM range. :woohoo:

The stuttering must have been from the loose slides...definitely wasn't the difference in air passage sizes.

I also changed the needle valve assemblies from 2.0 to 2.5. I can't imagine this was the problem though because it stuttered instantly....not after a long run...I couldn't get past half throttle at all. Then again, the difference in hole size from the 2.0 to the 2.5 is pretty amazing. I don't see the Mikuni logo on the 2.0's so maybe they are some aftermarket junk anyway.

Aftermarket. I did that with my 28's. It was OK with the stock cams but when I put in the 1X, I could feel it starving for fuel. Can't hurt. Good job.
Steve