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Old 04-14-2014, 03:59 PM
Geoinvt Geoinvt is offline
Motorized Bicycle Newbie
Join Date: Apr 2014
Location: Vermont
Posts: 17
Default Compression too high.

I've got a new 80cc (66cc) 2-cycle engine and jack shaft on a mountain bike. If I remove the plug I have no problem cranking the engine over. However, with the plug installed I can barely get the engine to move past the high compression spot. If I jump on the crank I can get the engine to turn maybe 120 deg. but not enough to switch from one foot to the other. Since I'm running a jack shaft I can't use the rear wheel to drive the engine. Does anyone have any tips for how I can get this thing started?

I'm going to temporarily disconnect the jack shaft from the engine and put the fixed sprocket, that the engine came with, on the rear wheel. This will allow me to use the bike to start the engine. It'll at least let me know that the engine will start. But, it won't fix my problem because it won't help me get the bike started when I run the jack shaft again. I also know I could put a thicker head gasket on but, I'm not sure how much this will really help me.

Has anyone else had this problem? Any suggestions? I'm not sure if these heads can be modified to use a decompression valve.

Thanks everyone - Geoinvt.
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