Compression Check

Patton, Keep in mind that Kaw wrote those manuals when these bikes were new... they don't take into account 30 year old antique bike characteristics. The 90-95 PSI readings will come up as the rings loosen up. I say this from a bit of experience... The 100 PSI service level provides adequate performance and realistically, most compression readings for old KZs that run decently are 115-125 PSI. The 160 plus compression wasn't on a stock KZ 903/1015... perhaps after a valve job, with new guides and a higher compression, aftermarket piston kit... but not with stock 8:1 compression ART pistons, even with new rings... that will get you a bit over 125 psi. The J motors have a bit more compression and I am only talking about the 903/1015cc...

wiredgeorge wrote:

Patton, Keep in mind that Kaw wrote those manuals when these bikes were new... they don't take into account 30 year old antique bike characteristics. The 90-95 PSI readings will come up as the rings loosen up. I say this from a bit of experience... The 100 PSI service level provides adequate performance and realistically, most compression readings for old KZs that run decently are 115-125 PSI. The 160 plus compression wasn't on a stock KZ 903/1015... perhaps after a valve job, with new guides and a higher compression, aftermarket piston kit... but not with stock 8:1 compression ART pistons, even with new rings... that will get you a bit over 125 psi. The J motors have a bit more compression and I am only talking about the 903/1015cc...

Thanks, WG. I concur. Believe FSM numbers are utopian figures in a perfect world. But gives me a goal to shoot for -- and miss.