Compression test

Reed Goddard

XS400 New Member
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Bc canada
Ive got an 79 that i picked up a few years ago, did timing and had it running but not well, i brought it to a shop to have a look and they basically told me it was junk because it had low compression.
Ive started up the project again and after resetting valve spacing im kicking the bike over and im getting a strangely high 170/175.
Im kicking it over because i havnt gotten it a battery or solenoid yet because i wanted to see if it was even worth before i spend to much money on it

While you were fooling around with it before, did anyone (like the mechanic) put some oil in through the spark plug holes to try and loosen the rings up? That usually explains the jump in compression. Low mileage (kilometer) engines normally develop low compression from stuck rings if they have sat for a while. It is not a fatal condition, and trying to "soak" the rings in something like Marvel Mystery Oil, Sea Foam, or ATF is an age old trick to free them up.