1975 RM 125 absence of power

[dix]

My cousin has a 1975 RM 125 with a fresh rebuild. The machine has no power whatsoever until you reach about 14k RPM's. Is this normal. I have to believe that something isn't adjusted right. I mean it's totally gutless until you get to the very narrow power band. To the point that you must ride out the clutch just to get moving. It will stall if you hold it at about half throttle and dump the clutch from a stand still. The carb seems to be jetted really rich, but only appears to have a main jet, and no other adjustment other than the air screw and idle screw. Am I missing something. This machine is a little too low tech for me!

 

[dirt bike dave]

Welcome to the world of pre-powervalve 125cc MXer's. Back then, peak HP was king, mid range was a rumor and bottom end was non-existant. The CR125s were even more peaky than the RM.

Powerbands were extremely narrow. These bikes can be very hard to ride if you are used to modern machinery.

Without riding it, it's hard to say whether its working right, but if you change '14k' to '9k' it sounds about like my '76 YZ125X.

Experimenting with the jetting, timing and fuel might help, but I would let someone familiar with that year's bike ride it and see what they think.

 

[dix]

I guess I was exagerrating a bit when I said 14K RPM's, but it does seem rather difficult to keep it in the sweet spot. I ride a 2001 KX 250, so this thing feels like its standing still. Wow, has technology brought these things a long way! Good to know that there is probably nothing wrong then.

 

[yzeater]

I rode one of these ancient bikes once. It was slower than my stock xr100. But....they must have been great, fun bikes when they were made:)