Lowering compression

[badtothebone250]

My friend just rebuilt his 250r, not knowing much about any previous work done to it. He bought it, ran it on pump 92 octane fuel, and melted right through the piston. Part of it I believe was because the carb was quite lean on the main, but after he just rebuilt it we ran a compression test and he is at 210 psi. From my understanding, a 250r with that much compression should be running around 105-110 octane fuel! Question is, can we stack a base gasket to lower the compression enough to get down to premium pump gas again or does he need to buy a new head!? Thanks!!!

[machwon]

Badtothebone250, you can do it with adding base gaskets but it depends on what the existing head is cut for. Adding another .02 to .03 in base gaskets would work, but this is a loser from a performance standpoint. If your friend is looking for the best performance on pump gas i would recommend he have a head specifically made for that purpose.

[rk88r]

Compare a stock 88/89 head gasket (it's quite thick) to the headgasket he was running. Stock heads are very easy to obtain also.

[265 sleeper]

Depends on what your friend has done to his motor . If he has a cylinder bored over to let's say 1 m over the head will not match the bore size thus creating more compression. Kicking compression is different than its real ccr. When the bikes running the compression is a whole lot higher than what you can kick prolly break you gauge if you hook it up. Ex port timing can also raise your ccr to low equals high comp . Aftermarket head s can help relieve some compression but doesn't mean your cc are correct . The true way and the only way I believe is to cc your head running pump gas you should be under 15:1 ccr. 17:1 is alky .