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Can't pull engine over with compression tester fitted

JohnnyDMonic

New member
Hi all,

I was servicing a Yamaha 2-stroke 4hp (4AC) the other day. It's is now running completely fine after fixing a few problems. Thought I'd do a quick compression test just to see, but with the compression tester in, I couldn't pull the engine over at all. There was so much resistance that I'm convinced the pull start cord would have snapped if I tried any harder.

Has anyone ever experienced this before? My only thought was that maybe the thread on the compression tester was long enough to foul the piston, but it doesn't seem that much longer than the spark plug.
 
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