rm125 - cuts in and out

[djm]

-i rebuilt the top end on this 91 -rm125 and its the strangest thing, i can hit powerband but after that it just cuts in and out, then i can shift into the next gear and it does the same thing.
-i've completely torn the carbs down and cleaned everything,
replaced the reeds and still the same problem.
- i once read some info on Eric Gorr's website that talked about the linkage on the exhaust power valve having to be right, but i have the linkage connected, just not sure what to look for, when i use the kick starter to rotate the engine i dont see the valve moving or anything (i've removed the head) althought its quite hard to see as the piston is moving up and down past the valve.
-anyone have any ideas as to why this thing is cutting out ?
-could it be electrical, like a bad coil maybe ?
thanks all :bang:

 

[Studboy]

I doubt that it is your powervalve causing the problem.
The powervalve won't open until 5,000+ RPMs, so I wouldn't expect it to be opening while I was cranking it over. I'm not sure how the powervalve is on that particular bike, but on most you could take of the cover to the linkage and start the bike and see if it is opening and closing.

Did this problem start just after the rebuild?

 

[wasted]

if it happend right after you rebuilt it, are you sure you didnt put the piston in backwards?

my brother has a '90 RM125 which to my knowledge is basically the same motor, if you want to check to see if the valve is working there is a cover plate on the right side of the cylinder behind the pipe that you can take off to see if the valve linkage is working and another on top of the cylinder to see if the valve itself is working...
you have to take the pipe off to get the side one off, then put it back on to start the bike...

how is the power of your bike after the rebuild? my brothers bike was supposed to have been just recently rebuilt but it doesnt have much power at all, I checked his valve and thats working good, I also looked up the exhaust port while I had the pipe off and it didnt look good, I'm positive it needs a major rebuild now but he's not sure if he wants to dump the money into it for just a marginal power gain or get something else...