VM22 Mikuni Clone Carb Tuning

[hmpumpkin]

Hey y'all, this is my first time on this forum so I apologize for any mistakes I make...

I recently got a GX200 clone engine from a generator that I put on a homemade minibike frame. I needed a new carb, so I thought I would go with a VM22 clone. Now it is running incredibly rich. There is tons of white smoke from the exhaust. As you can see in the picture, there is gas sitting in the carb air intake part. I'm not sure if the carb is flooding or if that happens normally. I've tried changing out the pilot jet for a #15, messing with the air-fuel screw, and changing the clip on the slide to the leanest mode but nothing seems to do anything. Also it doesn't idle right now, but I think that's just because of how rich it is. I could turn the idle screw in if I wanted. Any help is greatly appreciated!

Thank You in advance!
-hmpumpkin

 

[Master Hack]

There is tons of white smoke from the exhaust. As you can see in the picture, there is gas sitting in the carb air intake part.

Black smoke is fuel. White is mo bad. That short vid shows mostly water vapor orso it appears.

 

[Whitetrashrocker]

What does the spark plug look like?

Is the float and needle working properly?

Block up the rear tire so it doesn't want to run away from you.

Start with the idle air screw about 2 and a half out from lightly seated.

Get it running and adjust the idle air screw till the rpm are the highest. You might need to adjust the idle stop to drop the rpm down.

Once you get the air screw and idle set, then you can start working on the main circuit.

 

[vpd66]

What is bringing the fuel to the carb? Vacuum pulse pump or is it just gravity fed? Too me it sounds like a flooding problem.

 

[hmpumpkin]

The fuel is gravity-fed. I am almost certain this is a carb problem, because it ran perfectly fine with the original carb. This afternoon I'll try what Whitetrashrocker suggested.

 

[Hellion]

Mega kudos for the video and photos right off the bat, man. This thread is 10/10.

I agree with WTR. You have to get the bike off the ground so the back wheel can spin freely and so the engine can run a while. The engine ran for such a short time in that video, that it’s hard to tell what’s going on. The whitish smoke could be bore wear from its rough life as a generator (burning oil). At least that is my first impression. I’ve got an engine that will smoke a little on start up until there’s some heat expansion that seals the bore or expands the rings.

 

[Denny]

Can you tuna fish?

 

[hmpumpkin]

Ok heres the update...


I tried running it for a while and the smoke persisted. Even with the idle screw turned all the way in, it wont idle do to how rich the mixture is. I need to hold the throttle for it to run.

As for the spark plug, it was very black and when I rubbed it on something it turned it black with soot or whatever it is.

At this point, I think I'm set on the fact that this is a very rich mixture. I really don't think its oil because it ran perfect before the carb change and also the plug is black. Additionally, I think its something wrong inside the carb, due to the fact that changing the air fuel screw and jets doesnt seem to make any difference. Maybe I'll try switching it out for a very small jet like a 10 or something...

Lastly, along with the intense amount of smoke, it keeps backfiring thru the carb. Not fire or anything, but just a puff of fuel. This happens mostly when its about to die.


On camera its difficult to see all the smoke. There is quite a bit more than appears. After running it, the whole yard was smokey.

 

[Whitetrashrocker]

I hope that not rod knock.

Clean that plug or put a new one in and do it again. Looks very oily. Not gas.

Im gonna guess worn rings and a failing rod.

These engines are pretty simple to work on if you want to try to throw some parts at it.

Or a new one isn't too expensive either.
Working on them is mo fun doh.

 

[hmpumpkin]

Ok so a little while back, I replaced the crankshaft because it was originally tapered on the clutch side. I made sure to torque all the bolts to the correct spec. While I was in there I went ahead and removed the governor. I thought that knocking was the flywheel and the blower housing, because i accidently bent it while installing it. Now I have to use large spacers on the pull starter when bolting it on. Tomorrow, I will try removing the blower housing and see if the knock is still there. I really hope it is not the rod and burning oil, as that would be another Saturday of work doing an engine teardown and more parts to buy. I guess we'll see. What still perplexes me is that it ran perfectly fine (other than the knock) when I had the old carb. I see no reason why it would suddenly start burning that much oil. Maybe I'll try putting the old carb on and see what happens.

thnx for all the help y'all. Its very appreciated

 

[hmpumpkin]

Oh shoot! Come to think of it, I believe I might have way overfilled the oil. Whenever I went to fill it up after the crank replacement, I had it tilted up. Honestly tho that might not be a horrible problem... just drain the excess and see if that was the problem! I'll get back to y'all tomorrow in the afternoon

 

[Hellion]

This thread keeps getting better’n better.
I figured you mighta replaced the crank. Nice work, man. For most, I figure they won’t even go that far if the crank is wrong (tapered). They’ll just buy the right engine.

What’s the deal with the exhaust and/or that huge muffler? Another kudos to you if you’re trying to keep quiet in the neighborhood. What’s the opening like? Looks like the smoke is coming out of a drinking straw.

And use an air filter!

 

[Edwin Spangler]

Report back regarding the oil being too full.

If its not that, how long has that muffler been on the minibike? Is it new (newly added I should say)? Could have old residue. Ive had a scare just like that before.

-Or, no chance you put two stroke mix in, did you?

 

[hmpumpkin]

Ok sooo...
I definitely overfilled the oil... There was almost a half of a cup extra

As for the knocking, thankfully it was not anything internal. I took off the pull starter and removed the chain and the knocking stopped!

The whole exhaust setup (ngl the whole frame) is very make-shift. That muffler came from the generator, but it was designed to stick out the side, so I had to rework the whole intake part. I dont think it has enough backpressure to be doing something bad. I also have a few exhaust leaks that I need to deal with but thats not too hard. I would just buy a cheap amazon header + muffler although I live in a residential neighborhood without much property, so I want to keep it as quiet as possible so to not bother the neighbors.

The gasoline I use is straight from the pump. No special types or additives.

Ok so after draining the oil, It's still smoking. I don't know if running it overfilled could cause damage to the piston rings? Maybe theres just leftover oil that hasnt burned off completely? Maybe theres just a bunch of smoke still stored up inside the muffler? I'm not sure.

 

[Wicked_Daddy]

You mentioned earlier that you screwed the pilot mixture screw all the way in. That screws appears to be an air screw - if so, it controls the amount of air passing over the pilot jet to draw fuel into the intake path. Screwing it in makes it MORE rich.

Based the white smoke happening instantly at start up, It's not due to oil being in the muffler can. It's not hot enough yet to cause that if there were oil in it. It's burning oil in the combustion chamber and so much that it would be really hard to tell what the mixture is - rich or lean. I predict the rings are toast and possibly the valve guides as well.

Another thing to keep in mind is that these Chinese VM22 clone carbs can just be problematic out of the box. Sticky/leaky floats, bad circuits, too rich, too lean, etc. I've read several reviews of them on Amazon regarding these problems.

 

[hmpumpkin]

I thought it was a gas screw because it was on the engine side but maybe i was wrong. Anyways I just tried running it again with it all the way out this time and I saw no difference whatsoever.

At this point, I think yall might be right that its burning oil, but I'm still not completely sure.

Why I think it is still a carb problem:
Changing pilot jet/air fuel screw has no effect whatsoever. If I turned the screw so its in the leanest condition, shouldn't it refuse to run at all?
The smoke doesn't really smell like burnt oil (not that I really know the smell that well) To me its smells more like gas
It ran perfectly fine before the carb change and now it's suddenly smoking a TON without any gradual change.

If it turns out that it is a piston problem, then what do you recommend I get? Should I just buy a set of rings? What about a full piston replacement? Maybe a piston and connecting rod for only a bit more $? Lastly, what about a flat top piston?

Also, what are the valve guides?

This remindes me that when I was changing out the crank, the 2 rods fell out, so i put them back in thru where the ohv valve cover is. Because I dont have a feeler gauge, I wasnt able to set the valve lash perfectly. It seemed okay but I cant be certain. Does that matter very much or is it related at all to the smoke?