196cc carb help

[gretsch man]

Hey, just wanted to ask some carb advise. I recently got a coleman mini bike with a 196cc clone motor. I removed the governor, added an aluminum flywheel, 18lb valve springs and exhaust. I also bought a new mikuni vm22 carb. I installed the parts and it fired up right away with the choke on but the RPMs were pretty high and it was surging quite a lot. when I would take the choke off the RPM would stay high but stabilize and then stall after 3 seconds

Its a brand new genuine mikuni carb and the only thing I did to it was change the main jet to a 120.

I am not very good at diagnosing issues and dont have mech experience at all so any tips or advise and where to go form here would be appreciated.

 

[sparkwizard]

Check for an air leak where the carb connects to the intake. Pictures would help anyone who wants to guess, too.

 

[gretsch man]

Check for an air leak where the carb connects to the intake. Pictures would help anyone who wants to guess, too.

thanks for the advise. Im going to take the carb and intake off and make sure its all aligned good and tightened down properly in a little bit and test it. here are a few pics. not sure what screws is air/fuel and what ones is for idle

 

[sparkwizard]

That brass screw controls your idle SPEED. Back it out to lower your idle speed.

 

[gretsch man]

View attachment 319282
That brass screw controls your idle SPEED. Back it out to lower your idle speed.

thanks for letting me know.

I ended remounting the carb and intake and it fired right up and idled pretty good but for some reason every time I would take it off the kickstand and put it upright it would serge and die out pretty quick.. not sure what going on there.

also since I put the new flywheel on the pull start seems to lock on me once every 4 or so pulls and nearly take my hand off. any tips on how to avoid this or make it better?

thanks again for your help

 

[SAS289]

If it doesn't run the same on or off the kickstand it should be only one or both of two things. First, if you are using gravity feed from the stock tank make sure you have enough fuel in the tank. A nearly empty tank isn't going to feed fuel as good as a half tank. Next is the float. Is the float adjustment so far off that it is not allowing fuel into the bowl when the bike is upright? You'll need to look check the float adjustment.

Was the flywheel and 18lb springs put on at the same time? You should double check your valve lash. It's an easy adjustment as long as you don't set the exhaust side while it's on the compression release. Adjust them while it is just past TDC. Look this up if you have to.

 

[sparkwizard]

^^^That should get you going.^^^

 

[gretsch man]

If it doesn't run the same on or off the kickstand it should be only one or both of two things. First, if you are using gravity feed from the stock tank make sure you have enough fuel in the tank. A nearly empty tank isn't going to feed fuel as good as a half tank. Next is the float. Is the float adjustment so far off that it is not allowing fuel into the bowl when the bike is upright? You'll need to look check the float adjustment.

Was the flywheel and 18lb springs put on at the same time? You should double check your valve lash. It's an easy adjustment as long as you don't set the exhaust side while it's on the compression release. Adjust them while it is just past TDC. Look this up if you have to.

thanks for the tips, I appreciate it. After installing the new valve springs I put the motor to TDC and adjusted the lash according to the coleman manual.

I had issues with too much fuel line and not enough fuel in the tank when I first went to start it. I eliminated some fuel line to make it more direct and filled the tank to the top with fresh gas and thats when it fired up and started with the issues. I will tripple check it to see is I can improve it more though.. I think theres a good chance that may be still causing issues as you said.

I also installed a new throttle cable and used the adjustment at the handle bar to take all of the play out of the throttle grip. I am now reading things that say there should be a few millimetres of play in it. not sure if that could cause an issue like this but I will adjust it and see if it helps with anything as well.

thanks again for the advice

 

[SAS289]

Yeah i had the same thing with a lot of cable slack.

Best of luck with your carb tuning.

 

[gretsch man]

So I had some time today to see if I could get this mini bike issue figured out and I think it comes down to having bad fuel flow. The inlet on the mikuni carb I bought doesn't seem to be much lower than the fuel outlet on the gas tank. Has anyone else had issues with this before? whats the best way to raise the tank up a couple inches? or am I better off buying an aftermarket gas tank?

 

[sparkwizard]

Did it run right, before you swapped the carb? I think there is a little filter inside the tank...
I assume the tank is mounted above the engine. Those are tough to raise up. As stated above, it may run better with a full tank. If it does run better with a full tank, you could look at your frame to find a higher mounting point for an aftermarket tank, then start hunting for a tank that will fit in that space. You can also look into installing a pulse activated fuel pump.
I may get slammed for repeating this, but the original carb was already jetted and designed to run on that engine, plus in can be modified to perform very well. There are stock "blueprinted" carbs and "bored" stock carbs that (in my humble opinion) are easier to tune, work better with or without the governor and are MUCH easier to mount and are just a lot less hassle.

 

[gretsch man]

Did it run right, before you swapped the carb? I think there is a little filter inside the tank...
I assume the tank is mounted above the engine. Those are tough to raise up. As stated above, it may run better with a full tank. If it does run better with a full tank, you could look at your frame to find a higher mounting point for an aftermarket tank, then start hunting for a tank that will fit in that space. You can also look into installing a pulse activated fuel pump.
I may get slammed for repeating this, but the original carb was already jetted and designed to run on that engine, plus in can be modified to perform very well. There are stock "blueprinted" carbs and "bored" stock carbs that (in my humble opinion) are easier to tune, work better with or without the governor and are MUCH easier to mount and are just a lot less hassle.

Thank for the tips. it did run with all the stock parts on it but I only ran it for 5 min after buying before getting all the aftermarket parts and taking it apart. I have a feeling the inlet on the stock carb was a little lower than the inlet on my mikuni carb. I'm definitely not looking to switch carbs as this point though. That carb can be used on many more applications compared with the stock one so it made more sense to upgrade to the quality one for me. I also don't mind if its a bit harder to tune, id prefer to learn about it than just bolt on and go. I enjoy learning and tinkering as much as I will riding.

as far as the gas tank goes, I have a few ways I can see to raise it up but thought it might be worth asking if someone here has had experience with this so I can maybe save some time and use their input. I've also noticed some cheap aluminum cylinder tanks on amazon for a 100$ but they dont look to hold very much fuel at all.

 

[sparkwizard]

Look at vintage lawnmower tanks on Ebay. You might find one that would suit your needs. I buy them when I see them and now, I have more gas tanks than I need.