Tillotson 212 seems to be cutting out around 6000 rpm and not revving further

#21
I was afraid of that. I would invest in a fuel pump. Once installed you’ll probably be running very rich…try it.
More than likely you’ll have to jet it down ( leaner ) than it was initially. It’s sucking the bowl dry is my guess
Drill and tap your intake manifold for a clean pulse. You can pull it from a pcv line but you risk oil vapor in your pump.
i had actually tried a fuel pump before but it kept pissing gas out of the overflow lines, and no matter what needle size or float adjustment i tried, it would always piss gas out.
Was the slide opening up all the way? Where is he gas tank on this minibike? Can you post a video of it making the sputtering or misfiring? Your original video the engine sounds fine. As a troubleshooting tool you may want to put the stock CDI coil back on and make sure its not the new iginition system.
the gas tank is higher than the carburetor, so gravity has no issues getting gas to it. its not sputtering, it just wont rev past 6000 and it has power all the way up until that point
 
#24
Not an expert with these small 4 strokes, but built and raced 8 second 1/4 and 2 stroke dirt bikes since the 60's. It sounds good, I don't hear what I would call fuel starved sputtering or hesitation. I'm going with rev limiting electronics.
i talked with the guy who made the cdi he said theres no rev limiter built into the boards of them, he installed and tested them to like 10k rpm

even so my engine has been doing this for months it seems, went back and found a few things with the stock coil on and my engine still struggled to rev past the same barrier
 
#25
I would still try a different high output coil. Not sure, but timing ? I remember something in reading about coil to flywheel gap possibly affecting rpm's.
 
#26
ARC billet flywheel requires a minimum of either .040 or .045 for the Stock coil. Is the original coil OK? Are you saying you just swapped it and the same thing happened? Or you had issues with it earlier.
 
#27
By the way you should never open throttle a unloaded engine other than just blipping it. I does seem to be limited in rpm. If its not the coil and the ignition timing is OK (ie flywheel not slipped on the crank) kinda points to carb or valve float. Valve float will have a funny sound to it like getting quieter and some light noise emitting from the top of the head. The stock coil or original GX200 coils work just fine for these engines so unless you think there is something wrong with the original coil I would go back to it until you get this issue resolved, the play with the new ignition.
 
#29
ARC billet flywheel requires a minimum of either .040 or .045 for the Stock coil. Is the original coil OK? Are you saying you just swapped it and the same thing happened? Or you had issues with it earlier.
I had the same issues with the original coil, but ill still slap it on there and check to see if its the issue.
 
#30
By the way you should never open throttle a unloaded engine other than just blipping it. I does seem to be limited in rpm. If its not the coil and the ignition timing is OK (ie flywheel not slipped on the crank) kinda points to carb or valve float. Valve float will have a funny sound to it like getting quieter and some light noise emitting from the top of the head. The stock coil or original GX200 coils work just fine for these engines so unless you think there is something wrong with the original coil I would go back to it until you get this issue resolved, the play with the new ignition.
ill test coil tomorrow, and havent heard valve floating at all if it is what you described

i think it probably could be the carb, but what in the carb causes that kind of rpm limitation?
 

Minimichael

Well-Known Member
#31
Have you checked your valve train over? The first vid may sound a little floaty. The second vid may sound like it wants to give up near that higher rev. I don't know enough to comment on the 24lb springs, but could the lash be so off that it can't feed at that higher spin rate?
 
#32
Have you checked your valve train over? The first vid may sound a little floaty. The second vid may sound like it wants to give up near that higher rev. I don't know enough to comment on the 24lb springs, but could the lash be so off that it can't feed at that higher spin rate?
its been a while since i last pulled the cover off so it couldnt hurt to look it over
 
#33
did you check that the slide is all the way open? When you remove the valve cover make sure a valve is closed then push down on the valve end with your finger, if you have 24 LB springs it should be hard to move it. Don’t push it down too much or pushrod will fall out. Do that with both valves.
 
#35
did you check that the slide is all the way open? When you remove the valve cover make sure a valve is closed then push down on the valve end with your finger, if you have 24 LB springs it should be hard to move it. Don’t push it down too much or pushrod will fall out. Do that with both valves.
checked the slide and its opening all the way, will do that with the valves later today
 
#36
By the way you should never open throttle a unloaded engine other than just blipping it. I does seem to be limited in rpm. If its not the coil and the ignition timing is OK (ie flywheel not slipped on the crank) kinda points to carb or valve float. Valve float will have a funny sound to it like getting quieter and some light noise emitting from the top of the head. The stock coil or original GX200 coils work just fine for these engines so unless you think there is something wrong with the original coil I would go back to it until you get this issue resolved, the play with the new ignition.
fitted the stock coil back on, nothing changed
swapped back to electronic ignition for now since its hooked up

still have yet to check the valve springs, been busy all day with work and preparing to start my next semester of college
 
#37
It's a process of elimination and that was one More possibility you eliminated. I understand that 24-pound springs should allow it to rev higher, but the spring rate does not mean the seat pressure is 24 lbs as installed height varies. Or possibly they put in a different spring during assembly,
 
#38
It's a process of elimination and that was one More possibility you eliminated. I understand that 24-pound springs should allow it to rev higher, but the spring rate does not mean the seat pressure is 24 lbs as installed height varies. Or possibly they put in a different spring during assembly,
back on this, I just found a video of the motor revving past 6k. It was testing out when i first got the tm24 carb on my bike right now. it didnt have anything on the motor and it was revving perfectly fine. do you think the torque converter might be dragging my engine so much that it is limiting rpm?

I also found another video with my old clutch setup (same gear ratio) and it seemed to have revved past 6k just fine (and even went a little faster than what my bike can get with the limited rpm right now) 38mph is what i can muster with the limited rpm at the moment and in the video (https://streamable.com/10qgsr) the speedometer i had running in my pocket clicked around 41.4mph
 

SAS289

Well-Known Member
#39
Maybe. But the gearing you end up with after the belt shift should still be able to get more than 6K RPM with a 13 inch tire.

The difference in top speed RPM is expected because of the gearing change with the torque converter. You are using a stock 30 series, correct? It seems to be doing well because I can't even tell there's a belt shift from your video. RPM should drop off during the belt shift. Unless it's shifting before you give full throttle.
 
#40
you posted a video with the chain off correct? That eliminated the gearing. In that video were you holding the throttle open when it was running it sounded fine on the video but what rpm were you reaching without the chain?
 
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