I just did a compression test on the stock R I bought and it reads 150psi. Engine was warm, throttle open, about 8-10 kicks. Is this within normal limits? Remember the bike is all stock...
THANKS

 

The manual says 170lbs stock, so you may have a little ring wear.

 

That SEEMS a little low. However, there is a lot of variance among compression readings with the different types of gauges that are out there. There are basically 2 types; 1) the snap-on (brand) type where the schrader valve is right in the end of the fitting that threads into the spark plug hole, and, 2) the type that has the valve located elsewhere. The problem with the second type of compression gauge is that the volume of the air within the hose can alter your readings immensely. In a big engine, V8 for example, the compression chamber is quite large, and the small volume of air in the hose doesn't have much effect on the reading. In your 250R, it has a HUGE impact on the reading, because the volume of air in the hose can be almost as much as that of the compression chamber itself. If we where dealing with fluids instead of air, it wouldn't matter because fluid doesn't compress. But since we ARE dealing with air, that does compress, it becomes a great factor in getting accurate readings. Try comparing your results with a borrowed gauge of the snap-on type (the only one I know of to have the schrader valve in the "spark plug" fitting), to see if they are different.

Hope all that made sense!

-doug

 

I have been told that you need to open up the throttle when doing a compression test. This allows air to get into the chamber and give a more accurate compression reading. Make sure the gas is off when you do this.

 

My compression tester has about a 6" long hose going to the gauge and my readings were at 110 psi when I bought the tester (confirming my suspicious that it was losing power) then after a fresh rebuild and break-in it read 150psi and ran very strong.

Rod
02 400EX
86 250R