i have a 89 250r with some mods that has been done to the engine. i have put a .050 pro-x piston in it and also put a cr head gasket on it. what compression will i have when i finsh then bike off. will i have to run race gas through it. before i started the engine project i had 150psi. what do some or your bikes have for compression?

 

With a CR head gasket and not using two base gaskets your compression should be in the ball park of ~190-205 psi, after the motor is broken in. With two base gaskets it'll drop back down to around 185-195 psi. I advocate using two base gaskets to help lower the compression slightly and very mildly alter the port timings. With .5 mm different port heights it only alters the port timing by about 2 degrees duration, so there really isn't much to be gained there...but it certaintly doesn't hurt either. But more importantly it lowers the compression to safer levels with the stock head set-up using premium pump gas, while still getting the benefits of the increased compression.

Stock reading should be about 175 psi.

I've ran motors that ranged from stock 175 to current set-up at 260...martini's anyone???

 

I have done this mod on my dad's 86 250R and let me just tell you it rips! I only used 1 base and 1 CR gasket and I have had absolutely no problems. However, I do always use Torco 112 race gas(we can buy it out of the pump at the local station)so I don't ever worry about jetting for each new tank of gas or any detonation. Race gas is better anyway, it is cleaner and consistent unlike pump gas. If it is readily available, I suggest you use it exclusively. It will not make the bike faster, but it will run more consistently and the engine will last longer without all the impurities in regular Premium pump gas.

 

Do you guys test it with a hot engine? I have the CR head gasket and only get 155 psi, but I never tried it on a warm engine..

Rod 86 250R

 

Compression tests are typically done cold without any added oil or anything in the cylinder that would alter the reading.

If you've got the CR gasket and reading 155, you're coming due for a new piston (and bore if needed).

Variances in gauges can cause errant readings. I reccomend using only a Snap-On gauge. Other off brands use a hose that will throw off readings by adding more volume to your system and give lower readings than actual. Snap-On and Craftsman use a hose that has a valve core in the end of the hose that will show a more accurate reading.

 

Now my turn to ask a question. I just did a compression check on my LT250, and found it to be 190psi. Now, I have just got the motor togther on Friday and broke it in on Saturday, and some ridin' on Sunday. I used 93 octane pump gas, I checked the plug after a WOT run plug chop, and it is a light tannish white color. It runs right with my bro's Banshee (my bike is ported, piped, 38mm flatslide, etc..) but it feels flat on top, when the powerband kicks in, in feels like it pulls, but not ripping. It used to feel like it pulled alot harder, in comparison to my bro's bike it is, but just not feeling like it. Would race gas be needed for 190psi??? I am pretty sure the jetting is right on. But am looking for any advice. Later