Author Topic: Yoshimura 812cc big bore  (Read 300 times)

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Offline rokhedjo

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Yoshimura 812cc big bore
« on: December 11, 2020, 03:27:35 pm »
Any idea what the compression ratio was on the Yosh 812 big bore kit was?
1976 CB750 , 1986 V65 Magna , 2006 Kawasaki KLR650

Offline 754

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Re: Yoshimura 812cc big bore
« Reply #1 on: December 11, 2020, 10:57:02 pm »
Got a pic of the piston ?
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Online PeWe

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Re: Yoshimura 812cc big bore
« Reply #2 on: December 12, 2020, 07:33:55 am »
Probably made for stock chambers, around 22.5cc.
Compression make power, not too much though.

My bike became happier when my cheap compression tester showed 200PSI instead of earlier 170-190 area with different cams with my old head.

Last head with smaller chambers popped up the dyno chart.
Previous head had even 5mm stemmed valves and ported more.

Online Jerry Rxman Griffin aka MuthaF'er

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Re: Yoshimura 812cc big bore
« Reply #3 on: December 12, 2020, 08:54:39 am »
Mine is likely 10.25:1 or 10.5:1. It is NOT 12.5:1. Works fine with stock head and Yoshi Daytona cam and HD springs.
As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)