Roketa Tahiti 150cc stalling and dying when stopped  By  johnathonkreider (Read 4,424 times)

If it happens after it warms up, check th valve lash, probably too tight.

Luckily JR has put together a great video section here with instructional videos that walk you thru it

itistheride.boards.net/thread/8227/90gtverts-gy6-valve-adjustment

So an update. I adjusted the valves, and that took care of the problem of the scooter stalling when I stop (I also adjusted the idling rpms and changed the oil), but I still have a problem: after getting up to about 35mph, my engine will start to stall out, and die, regardless of how much i give it. I looked at my engine, and I see that the hose going from my air filter to my carburator is a bit frayed. Could that be the issue?

I have checked the carburetor to make sure it moves smoothly, cleaned the jets, the float floats properly, and everything moves smoothly. Could it be an airflow problem? There's nothing that is jamming the air hose, but it is pretty frayed on the end where it attaches to the carburetor. Also, could this be related to electronics? My electric starter recently stopped working.

i would imagine your CDI / coil are both ok, the fact that it starts up tells me that they are doing there job well, a bad CDI or coil would mean inconsistent spark (a bad CDI usually means no spark at all) all the time the only exception here would be unless your coil cap is loose on your spark plug and at high RPM it is vibrating enough to cause the issue you are having but i would expect to see a little bit more inconsistancy in the issue you are having if that was the case.

what does your engine need to operate? gas, air and heat. the fact your bike runs and runs well upto a certain speed tells me your engine is getting everything it needs apart from when you increase the RPM's, as you increase them you increase the ammount of fuel and air you need so i would say you are either not getting enough fuel / air through at that speed or an incorrect mixture making your engine struggle. i would quite happily rule out your coil cdi and spark plug at this point

have you had it on its centre stand at full throttle? does it struggle at all or seem to get upto a certain RPM and not want to move past that?

one way to test the air filter theory would be to (and only do this for a very short time) take the air filter off and take if for a test run when you have good weather somewhere clean no dirt or grit etc you dont want that getting your engine...
if it runs fine with the air filtet off then you have found the source of your problem, clean / replace.

if its still the same with the air filter off them you can rule that out also. (check the rubber for cracks also! a small crack could be letting too much air through)

at this point we have ruled out heat (your spark plug) and air, next i would check your inlet manifold is tight and the carb is seated tight into it, if this is slightly loose then again vibration at high RPM could be moving it about allowing extra air in screwing with your air / fuel ratio and losing vaccume to the carb.

if this is all good then we move onto fuel, your carb would be the main suspect here checking your main jet would be the first thing but you said you have already done that (what did you actually use to clean the carb?) its unlikely to be your fuel lines filter or petcock valve as you are getting gas, however if your filter is blocked you may only be getting enough gas into the carb for lower RPM's it may be that your carb float bowl is emptying out faster than it can be filled due to a blocked filter at High RPM's but again this is unlikely the way to check this would be run it at high RPM's or 35mph where you have the issue for as long as possible. then check the carb float bowl if it is full theres no issue with your fuel line filter or fuel vaccume line if its empty work your way up.

do you have any spares? does your friend have a bike with the same carb? could you swap to test?

let me know how it goes and if still unsuccesfull ill come back with more ideas.

you mentioned the ducting from your air filter to the carb frayed. if you mean it's letting in air then that could very well be your problem. the system is actually "tuned" so to speak. all the talk at times of opening up the intake to create power yada yada had me for the heck of it try without the filter cover on (it's only got a little hole for the intake air). any real throttle it was crap, such as you describe. i also know of many that try the little cone filters right on the carb only to throw them away and keep it stock for this exact reason. a little leak may not cause much of a problem but if torn yes.