Hi guys... i recently got my daughter a scrappy Aeon Cobra 100cc Two Stroke that was not running ... after doing a quick check I got a new battery and discovered the motor was swinging very slowly. I stripped the motor down and checked the piston - showed not wear .... and reassembled it with new gaskets... same issue - I then checked the rear clutch and found that the gearbox oil had all but gone and turned to sludge. I changed the oil along with the outer bearing and new drive belt.....Motor still had the same issue . I then turned to the Starter and installed a new starter... same issue. I then removed the spark plug and the motor seemed to turn much better, but once I install the spark plug it turns once or twice and then on the compression stroke just slows to almost a stop. Any input would be appreciated - currently the motor turns slowly even after I have removed the drive belt / front variator with rollers as well as the Reed Valve... and still once I install the spark plug the motors turns slowly .... note that the battery is connected directly to the starter terminals and not via the wiring harness. Compression test shows around 90 PSI.

 

Most likely is a flat or dud battery. If you have eliminated that, the starter clutch slipping can cause this, as the most likely time for it to slip is at maximum compression and, if the piston stops then, it is just as the engine fires, so starter trying to shove engine forwards and piston trying to shove engine backwards, because spark is just before TDC.

 

Thanks Merryman ... I did try a new battery and same issue - as for the starter clutch - I did clean it up..cleaned spring - rollers etc .. -- but not seeing any signs of clutch slipping ... next step is to try and swap out the piston/rings and see if it has any impact .. currently motor is out of the ATV - on my work bench - with just basic to test the compression action