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Discussion Starter #1
I have an 82 Z50 that ran great but was starting to smoke so I put a new piston and ring set in and honed the cylinder. Set valves to 0.02 intake and 0.03 exhaust. However now I’m only getting 60psi compression. Bike idles just fine and runs great in neautral. But under load it can hardly make it up a slight incline. Flat ground is ok but almost dies going up a hill. Any info would be great. I know compression is low but it did run great before hand. Note, I didn’t do a compression test prior to rebuild. Any help is greatly appreciated!
 

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Two questions: have you ridden it enough to break it in? and have you re-torqued the head? The compression will not be to its highest until the rings are seated. Usually, a 20 minute ride accelerating and decelerating (using the brakes as little as possible so you are using engine braking) with a post-ride oil dump will do the trick. If the head is too tight or too loose, you can lose pressure there.
 

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Discussion Starter #3
have ridden probably for about 10 minutes but will hardly pull me around. Will recheck torque again
 

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Are you sure you used the correct piston? Long rod vs short rod type?? Did you check the deck height? Can you give us a link to the piston that you used?
 

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Try and do a compression test after the bike is warm and hold the throttle wide open, you'll probably get better results. Also you really need to turn engines over fast to get them to build pressure. Might help eliminate the possibility of low compression if you can get better numbers and move on to other possible causes for the bad performance.
 

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I guess his issue is less the actual number but more the fact that it barely has any power.

Short and long rod piston mistake could be something. Do you recall how far down the cylinder the piston sat at top dead center?


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