Need Help Desparately with 650sx

[rmv6]

Hey guys, i'm trying to slowly hop up my 93 650sx, not sure where to go from here though. Right now the ski has ocean pro ride plate, and mariner waterbox. I just installed a mariner head and put a compression guage on it and it read 180 and 195. Is that way to high for an engine that is all stock besides that head? I also have a Coffmans pipe on the way, but no aftermarket manifold. How is all this going to work together and what does it mean for my 38 Keihin carb? Compression way to high? And what pitch prop should i get (have stock prop on now) with all those parts installed (if they will even all work together)

Thanks a for the help, i'm new and trying to avoid wrecking my ski.

 

[chrisdoc0608]

180 is pump gas safe...195 not so much, but when you are getting both of those numbers with the same head thats not good either. ideally your compression will be equal on each cylinder. if you run 195psi on just pump gas you can risk detonation and do damage to your motor.

 

[rmv6]

reffering to pump gas do u mean 87 octane or 93 octane (if that's what premium is)

 

[delagem]

Both of those are pump gas. Neither provides enough margin of error for 195 compression.

You need to figure out two things: why is only an aftermarket head causing such high numbers, and why the difference between the cyl's.

10% is the commonly accepted limit for difference between cyl's, and you are within that, barely.

Are you sure you did the test the same way for each cyl? Is your battery good? If your battery is marginal, the second cyl you check will read lower, as your motor cranks over slower.

Hook up a set of jumper cables to another battery (like your car) and try again.

Are you running a copper head gasket, or base gasket? Or no base at all! Did somebody deck the cyl before you got it? Or the head?

Michael

 

[sflsurfrider]

i would re-check your compression a couple times to ensure that is the correct psi.

 

[WFO Speedracer]

There seems to be a disparity on the deck heights of the Kawi 650 cylinders from the factory,some were considerably shorter than others. That is why some 650's scream and some run poorly.Back in the day when Bad bones was into racing Jeff Pruifer was disqualified after winning the world finals because of a short cylinder,the cylinder was untouched other than porting done by Bad bones.It did not matter,KAWI owned IJSBA back then and they would not own up to the cylinder problems,he was still disqualified.Shortlt afterwards Bad bones pulled out of racing, closed up the pwc acc division and started producing Harley parts.

 

[rmv6]

its a metal gasket on there right now and I checked both cylinders about 3 times and in different order with same readings everytime. I'm really lost from here though what should I do with this head issue and what risks do I have with running it as it is?

 

[WFO Speedracer]

I would pull the top end down and see what is causing your compression loss on the other cylinder,thats first,when you have that resolved send that head to group K tell him what bore size you are running and what you want the compression to be.What you want is 175-180 max for pump gas and reliability.He can recut the head to suit your needs since you will be lowering the compression.