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HELP: RM125 will not hit power band!

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My 1995 rm125 will not hit the power band no matter how much I rev it. It will rev up in nutreal just not in gear driving I just did a top end and the power valve is not sticky or anything and the bike won’t idle but will still run if your on the gas and I just cleaned the carb to plz help

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Posted (edited)

That's an old engine, when were the reeds last replaced, float level adjusted?

Have you ever fouled the plug, cleaned and re-used it?   If so, try a new one.

Pilot jets have such a small orifice that when plugged up it's often preferable to replace it rather than attempt to clean it.

 

At the very least you should perform a crankcase leak down test to rule out an air leak.

(see the how-to sticky in the Honda 2-stroke sub-forum)

Edited by mlatour

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So your power valve is seemingly fine, carb is clean, revs fine in neutral, newer top end.

Possible gearing issue / bottom end / clutch? Shifting fine through all gears? Guessing so. Crank/tranny issue? Grasping here—but top end/fuel/piston all seemingly ok and you mentioned ‘when in gear’ it doesn’t behave hence bottom end. Wish I had more. Experts will do better than I.

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So your power valve is seemingly fine, carb is clean, revs fine in neutral, newer top end.
Possible gearing issue / bottom end / clutch? Shifting fine through all gears? Guessing so. Crank/tranny issue? Grasping here—but top end/fuel/piston all seemingly ok and you mentioned ‘when in gear’ it doesn’t behave hence bottom end. Wish I had more. Experts will do better than I.

I took the side cover off for the power valve and it’s not even attempting to move when it’s running it just kinda shakes but I can move it by hand when I shut it off

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Posted (edited)

The powervalve usually only starts moving at 8500-9000 rpms or so (say by 3/4 throttle)

so if the engine wasn't revved up that high while running on the stand, the PV governor won't kick in.

Edited by mlatour

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The powervalve usually only starts moving at 8500-9000 rpms or so (say by 3/4 throttle)
so if the engine wasn't revved up that high while running on the stand, the PV governor won't kick in.

Ok but why won’t it kick in at all when it’s running

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Because you're manually by-passing the governor.

When you move the linkage, there should be a bit of tension to overcome to open and,

it should return to the valve closed position by itself when released.

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Ok but why won’t it kick in at all when it’s running

It sounds like it’s bogging cuz when it get up in rpm the power valve don’t kick in

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I have a 1995 rm125 that won’t hit power-band the reeds are good the carb is good the power-valve is good and I just rebuilt the top end but it recently lost spark could the coil or the cdi box be the problem of the power valve not opening any help will be appreciated.

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I have a 1995 rm125 that won’t hit power-band the reeds are good the carb is good the power-valve is good and I just rebuilt the top end but it recently lost spark could the coil or the cdi box be the problem of the power valve not opening any help will be appreciated.




Are you sure you don’t have a bright blue spark?
If the answer is yes then disconnect the kill switch and try again. If that doesn’t work then clean all of the contact points where the coil meets/touches the frame use sand paper to clean the frame and coil in those areas and wire brush screws. Same goes for the stator. Use PB blaster in the screw holes and run the screws in and out a few times. If there is still no spark then remove the spark plug cap and cut about a 1/2” off the wire and install a new cap. If that does not work then it’s time to go deeper. In almost 40yrs of dirt bikes I have never seen a CDI go bad. It’s always been a bad ground or broken wire somewhere bin the system.
Good luck.

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Recently lost spark can be as simple as a fouled plug. Change the plug and make sure the old one is not black and soaked with fuel. If it is then your running pig rich hence the bog on the top end. Install a fresh new plug and air filter and try again. 

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