VM22 boggs with throttle

[TheMattHouston]

My son and I got 2 Coleman B200R mini bikes with the intent of learning how to work on carbureted small engines. The first thing we did was purchase a VM22 kit on Amazon that came with the throttle cable and adapter.

Immediately after installation when giving throttle the minibike bogged and stalled. We had done some research so first thought was intake leak so we pulled it off, checked seals and gaskets and reinstalled to find the same result.

Maybe it's fuel so we adjust the needle but it was already maxed out. We tried larger main jets but the same result no matter what.

I just finished reading a great article https://www.vintagebikebuilder.com/mikuni-tuning-and-jetting-guide.html but still can't find a solution. is it possible it's just a bad carburetor? What should I try next?

 

[DR&R]

I've always had very good results with use of the vm22 on all the bikes I've used them on and have actually yet to run into a bad one myself. from my experience whenever there was a bogging problem it usually traced back to a air leak or generally lean condition. the tricky part is how to configure the carb to the manifold since there's so much adjustability on it. the best way is to assemble carb to the manifold first so you can look down the bore to make sure the O-ring lines up perfectly to make the seal proper, when it's offset any bit is what causes the air leak to sneak up on you. after those 2 are lined up proper then the manifold can be bolted to the cylinder head itself. as far as the main jet is concerned, they're always on the lean side out of the box, usually on a stock motor or even with minor mods, a 120 main is usually suitable or at least a good starting point. as far as that clip goes on the needle, I usually tend to just leave it in the middle position like it tends to be from out of the box. I've never really had to play with needle position on any of my setups, they haven't tend to be as sensitive as the 2 strokes that I used to tune/ride.

 

[TheMattHouston]

I've always had very good results with use of the vm22 on all the bikes I've used them on and have actually yet to run into a bad one myself. from my experience whenever there was a bogging problem it usually traced back to a air leak or generally lean condition. the tricky part is how to configure the carb to the manifold since there's so much adjustability on it. the best way is to assemble carb to the manifold first so you can look down the bore to make sure the O-ring lines up perfectly to make the seal proper, when it's offset any bit is what causes the air leak to sneak up on you. after those 2 are lined up proper then the manifold can be bolted to the cylinder head itself. as far as the main jet is concerned, they're always on the lean side out of the box, usually on a stock motor or even with minor mods, a 120 main is usually suitable or at least a good starting point. as far as that clip goes on the needle, I usually tend to just leave it in the middle position like it tends to be from out of the box. I've never really had to play with needle position on any of my setups, they haven't tend to be as sensitive as the 2 strokes that I used to tune/ride.

I appreciate the knowledge. I took the carburetor off again and was looking over everything and there is a small tear in the O Ring that sits in the adapter. I never took it out of the adapter during assembly so I have no idea how it happened. I got a package of assorted carburetor O Rings from the auto parts store and none fit. So now to track down the correct size O Ring.

 

[hermans13]

Some well equipped hardware stores carry trays of O Rings in assorted sizes. Take the original with you and try to match it up.

 

[RobertC]

Here's my thoughts y'all, and this is just my uneducated hunch.

As far as I know, you must disable the governor to run a slide carburetor.

That said, have the safety mods like billet connecting rod , and flywheel been done ?

And how was the governor then dealt with ?

Was it removed as needed, or is it still in there, flopping and bouncing around ?

 

[MJL]

What jet sizes are you using?

 

[sparkwizard]

Here's my thoughts y'all, and this is just my uneducated hunch.

As far as I know, you must disable the governor to run a slide carburetor.

That said, have the safety mods like billet connecting rod , and flywheel been done ?

And how was the governor then dealt with ?

Was it removed as needed, or is it still in there, flopping and bouncing around ?

^^^^^^^^^
Very important.
Just my opinion, but I'll bet if you put the stock carb back on it, it won't bog anymore.
After you get the billet rod and flywheel, remove the governor while you're in there, then figure out how to make the motorcycle carb work on it.
Is your engine even broken in, yet?

 

[TheMattHouston]

Here's my thoughts y'all, and this is just my uneducated hunch.

As far as I know, you must disable the governor to run a slide carburetor.

That said, have the safety mods like billet connecting rod , and flywheel been done ?

And how was the governor then dealt with ?

Was it removed as needed, or is it still in there, flopping and bouncing around ?

I attached the spring to a similar location on one of the mounting bolts and got a tachometer. The engine now revs to 5500 rpms before the governor kicks in. I will remove it correctly and upgrade the internals soon.

 

[TheMattHouston]

^^^^^^^^^
Very important.
Just my opinion, but I'll bet if you put the stock carb back on it, it won't bog anymore.
After you get the billet rod and flywheel, remove the governor while you're in there, then figure out how to make the motorcycle carb work on it.
Is your engine even broken in, yet?

Yes, It has 10+ hours on the one we are modifying.

 

[TheMattHouston]

What jet sizes are you using?

I tried 120 and 125.

 

[MJL]

I tried 120 and 125.

Have you tried a larger pilot jet?

 

[ole4]

If it bogs and stalls when you try to open the throttle the last thing you should have done was change the main jet that only affects the range from about 60% throttle and up. it appears that either you have a air leak or your pilot / slide height adjustments are off. Be aware they work together to control your idle and off idle response.

 

[TheMattHouston]

If it bogs and stalls when you try to open the throttle the last thing you should have done was change the main jet that only affects the range from about 60% throttle and up. it appears that either you have a air leak or your pilot / slide height adjustments are off. Be aware they work together to control your idle and off idle response.

I have the new O Ring and order some pilot jets so I will start with the O Ring and then pilot jets if I still have the issue. Thanks for the guidance, I'll get in there and play around some more this weekend.

 

[ole4]

Which type of pilots does your chikuni use?

 

[TheMattHouston]

After talking to the Amazon seller they sent me a replacement and it works fine. Thanks for all the help.

 

[MJL]

After talking to the Amazon seller they sent me a replacement and it works fine. Thanks for all the help.

Awesome, was it advertised as being jetted for a GX200(or clone)?

 

[TheMattHouston]

Awesome, was it advertised as being jetted for a GX200(or clone)?

Yeah, it listed the stock 198cc the predator and all the Coleman mini bike models. it was this one. They sent me the replacement for free and asked I send the faulty one back.

https://amzn.to/3v6qJTD

 

[MJL]

Nice, did some carb shopping a while back and never stumbled into the ones jetted for a 196/212, apparently there are tons of them available. Glad they made it right for you. +1 for getting your rod and flywheel replaced asap. My boys have about outgrown it now, but riding/upgrading/repairing minibikes with them was some of the best fun we ever had! Enjoy it!

 

[Strigoi]

After talking to the Amazon seller they sent me a replacement and it works fine. Thanks for all the help.

That's the best option. I've used a lot of these Chikuni 22mm carbs and they're hit or miss if they work well. I've had some that take almost zero tinkering and others where the bike won't run right no matter what I try. I'll swap to a known good one and the bike runs great.

Honestly, I wouldn't run that engine until you get the billet parts and remove the governor. At the bare minimum, get the governor assembly out of there. I've had a bypassed one come apart inside the engine. Luckily there was no damage as the engine only had a few minutes of run time on it.

 

[TheMattHouston]

That's the best option. I've used a lot of these Chikuni 22mm carbs and they're hit or miss if they work well. I've had some that take almost zero tinkering and others where the bike won't run right no matter what I try. I'll swap to a known good one and the bike runs great.

Honestly, I wouldn't run that engine until you get the billet parts and remove the governor. At the bare minimum, get the governor assembly out of there. I've had a bypassed one come apart inside the engine. Luckily there was no damage as the engine only had a few minutes of run time on it.

I thought the internals were good until 5800 rpms. I do plan on doing it but since I was able to set the spring up to cap the rpms at 5500 I would be okay to run as is for a month or two. My son's birthday is in February and that's when I was going to buy all the internals.