could be an air leak at the base of the cylinder. as the metal expands it causes some imperfection in the cylinder or crankcases to open up enough to let air in. I'm not sure if that's what it is, but it makes sense in my head haha.
RM250 rm250 high revving possibly an air leak
- Thread starter 2strokeseatmakr
- Start date
Nighthawk that does sound like it does make since the top end was done just before this started to happen. Looks like I need to remove the cylinder and replace gasket. I was pretty sure it was a air leak some where. you dont think the Reeds could be causing this. I took them out cant see any visible crackes. Are they supposed to close pretty tight there is a tiny little gap on one side
there should be NO gap
like she said no gaps anywhere. If there is a gap it will cause a massive air leak and make your bike rev like an air hammer
The gap is at the tip of 1 of the blades they are carbon fiber. But that would make it rev all the time right not just when warm or hot.
oh.. I thought you meant the reed cage, no that wont make it do the high revs. im thinking cylinder base. Check your torque specs and try retorquing your base bolts, same with the cylinder head bolts
There is a rubber seal between the cases and the crankshaft. It keeps air out just like the gaskets do. When you fork seals fail they let the oil out. when a crank seal fails it lets air in. Normally they are easily replaceable.
Here is a pic
My book says the reeds should not exceed the service limit of .2mm. So if there is a service limit, then wouldn't there be some kind of gap allowed? If they are cracked or chipped now that is different. If they were leaking air it would do it constantly as would the crank seal on the stator side. They clutch side would cause a oil leak and would lead to excessive spooge and loss of clutch oil. I believe NH nailed it with the cylinder base gasket leak.
Thanks to all I will try to replace the base gasket and re torc the nuts on the barrrel and head. Ill let all know the outcome.
DAN, MY FRIEND, YOU'RE king of the friggin' hill!! YOU WERE RIGHT ON!! I wanna thank you...she's running like a dream! It was just as you said, the filter's fine, no air leaks, header's snug...put premium in it, fresh pre-mix, choke, no throttle, routed the cable right, and Vroooom! she started about the third kick and just runs awesomely! thanks so much, all the other advice had me panicked, thanks for the grounding, and rational path....Mind what you have learned; save you it will!! lol...thanks again!...now, to get that crappy black rattle-can off the rest of the plastic...
Forget trying to pick the spray paint off and just 
it 