5 hours on top to bottom engine rebuild. Last 2 times at the track, the thing just revs straight to the moon on a cold start, and revs don’t drop unless I turn off the choke. But when the bikes warmed up, it idles like it’s supposed to, which is barely at all. So that struck me as odd.
On top of this, the engine sounds weird under load, instead of being smooth and harmonic, it sounds coarse. And it is also significantly down on power, especially under load it’s just a complete dog. Won’t lift the front in first and loses steam up any hill sections. Compression is still great, plug looks fine/darker.
I just dumped $2,500 into the motor. Parts and labor. What could be going on now.. this is exactly how it ran right before it locked up last time. 2000 rm125
Have you done a leak down test (either before or after the rebuild)? That's where I'd start (assuming it's not a mis-routed throttle cable or something like that). Sure sounds a lot like an air leak. What does your plug look like after you've ridden it?
+1 on the leakdown test, I have had RM125”s that leak air right through the cases due to porosity….. search 2t leak down test on Utube…this should be done after any rebuild….other things to check, as stated: throttle cable routing, carb slide hanging up due to wear, partially clogged jets, worn carb orings/ gaskets.
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