Rotax 125 , clutch issue

i have an issue with my clutch on my rotax 125 power valve motor, when i fire up the motor clutch engages and stay engaged even at a low idol. took it apart and everything looks good. Does anyone have any ideas as to what my problem could be. Thanks Jeff

How old is the clutch pack? How has it been driven?

This problem can happen if the shoes get glazed or warped slightly.

Also wondering if you can take a picture of the clutch drum or the shoes, that may help.

Does the drum spin freely when the engine is off?

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Hey Eric, yes drum runs free when engine is off, I will get some pictures tonight.

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A Rotax clutch can drag a bit at low RPM but it shouldn’t drag. I’m presuming that you have the kart on the stand. Check the engagement with the kart on the ground, should be right around 4000 RPM. If the kart bogs on ground while taking off, I would say there is a problem with the clutch shoe assembly.

I’m presuming this is the newer flexure version (not the one with springs), if so, take really close look at the flexures and make sure that one or more of then are not cracked or has been distorted. As a word of caution, do not operate the engine without the clutch housing, as the flexures will likely be damaged.

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Thanks Larry, it is like clutch is locked in at all times either on the ground or on the stand. I will pull it back apart tonight. and get some pictures also…Thanks again Jeff.

Anyone going to Kart week in Daytona to watch ??

Found crack in drum. I believe this could be my problem.


I believe that would be your problem, almost assuredly the drum is flexing abnormally at high rpm. I see you updated the post with some photos of the clutch pack which looks absolutely cooked unfortunately.

Replace both and you should be back to running. Wish it was better news and less $$$

Do you have any ideas how the drum cracked? I can’t say I’ve seen that before….

Are you installing the clutch correctly?

You have the thrust washer on the inside?

Is it an 11 tooth sprocket? If so, are you using the correct smaller washer? The 11T requires a smaller washer than the 12/13T.

If it’s 11T check to see if the bushing is cracked. If it’s 12 or 13T is the needle bearing shot?

No, Not sure how drum became cracked, I just bought this motor from a guy as I am rebuilding a kart from scratch CRG Intrepid and finally got the kart ready for the motor and that is when I found the my problem. thanks for the advise. I will order new clutch and drum tomorrow

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Hey Andy, clutch is installed correctly. I have a 13 tooth sprocket on it with the bigger washer. I just picked this motor up second hand and installed it on the kart and this is what I found. Thanks for your help. Jeff