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Discussion Starter #1
Gents

I bought this piece from someone who claimed they bought it with the intent of getting it running. They claimed they put a new piston and rings in it but can't get it to start because "it's back firing through the carb".

So I by it and start tearing it down. It does appear like the piston is new, and the cylinder is in very good shape. The piston size is stock, or 71.96mm. The cylinder is in very good shape as he said. The rings had 0.008" gap at the ends so they are very snug.

I put everything back together. I tried to start it and it did indeed backfire through the carb. Looking further I realized that the engine could be easily rotated by hand, virtually no compression. I am at a loss trying to understand why I have no compression. The rings and piston seem well matched to the clean bore. The crank seals should not have anything to do with compression??

I have not measured the compression, but you can turn the pulleys with almost no resistance. Also, when you put your finger over the plug hole there is NO compression resistance.

yet everything measured well??

Please help!

Thanks
 

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Discussion Starter #3
When I tore it down, I put everything back together right. It had a new Namura piston in it, stock size (71.96). The ring end gaps were plenty tight 0.008" maybe even 0.007". The piston to cyl clearence is tight too, no more than 0.002". Cyl walls were freshly honed, no scars. Gaskets are good. The "ex" mark on the piston was facing towards the exhaust.

I can rotate the crank by hand with virtually no resistance. Free to spin.

When I tried to start it, it fired out of the carb! Other than that it sounded dead.

I'm at a loss why it's so loose.
 
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