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Discussion Starter · #1 ·
k here is the deal. We just got a indy 500 fuji, said it had a new top end, but i did a compression check after i got it home and it only read 90 psi on each cylinder. I know there not a high compression engine by any means but 90? something doesn't sound right
 

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Yeah that aint good. Chances are your comp tester isint off by that much. If you did the comp check right (held throttle open and pulled 5 or 6 times)then Id say they messed up their top end rebuild. Prob best to pop it open and do the rings yourself so you know what you got.
 

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your compression should be around 125 psi, run it, and see if the rings are just stuck in the lands, but likely the cylinder was bored wrong, or the motor was not really rebuilt.
 

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Discussion Starter · #4 ·
at first i thought it was my sucky compression tester i got from harbor freight for $10, then i did one on my xc and it read the same as my more expensive compression tester. Ill run it and if it blows up it blows up. It starts 1-2 pulls hot or cold though
 

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I doubt itll blow up caus of that. Itll just get harder and harder to start as you lose compression over time just from normal wear, but thst might take years. IMO, if its your backup sled, run her, like you said. If it runs good thats all that matters.

How new is the top end rebuild? If the rings arent seated yet, then you might gain comp as you ride it. Just a thought.
 

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Discussion Starter · #6 ·
Thats exactly what i was just thinking, the motor has almost no run time on it. It also pulls over harder then my xc 600 with 120 psi comp..

I might just be worrying too much haha
 

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If the rebuild is very fresh, it is possible that the rings haven't set yet. As with any motor rebuild, be sure to do proper break-in period.
 

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My Fuji 400 NEVER had 125 PSI; after rebuild, or breakin. 90 sounds a little low though.
 

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Discussion Starter · #9 ·
Im just curious to why they did the rebuild, of course i didn't ask, but usually these motors are hard to kill
 
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