I didn't a compression test on my 94 600 that I just purchased and I am getting 210-220psi on all 4 cylinders on a warm motor. Factory spec is 190psi. I cranked the motor over until I achieved the highest number on the gauge. Any clue why my compression is so high?? Is it possible I have upgraded pistons?

 

Do you have an aftermarket can...that may increase the back pressure.

 

Are you sure you are using the compression tester correctly?

I thought that you were only supposed to turn the engine over a certain number of times (3?) to get a proper reading.

 

The cylinder can only produce so much pressure and you want to measure max psi. Instruction manual with the gauge said to crank the motor until the pressure stops climbing. I also read many online write ups on checking pressure this way. I even checked PSI with a different gauge.

Aftermarket exhaust will decrees back pressure as most mufflers are strait through.

 

The exhaust should make no difference to the compression tester. The compression tester is only reading the amount of pressure that can be created in the cylinders when the valves are closed. You can take the exhaust off, and still get the same readings because you are not flowing enough air through the exhaust to have any effective backpressure.
You did the test correctly, warm motor etc...but the only thing to add, is to hold throttle wide open to allow the motor to suck in enough air to compress.
The better test to do, if you checking your motor is a leakdown test. This will give you an indication of what the problems are if any. In this test you apply compressed air into the cylinder (tdc compression stroke), through the tester, and measure the amount of air that leaks out in percentage. Checking where the air is coming from, if it is leaking will tell you whether you have a ring, intake valve, or exhaust valve problem. If you google Leak down testers, there are lots of DIY pages on how to make the tester, and how to do the test.

 

Gsx is right exhaust doesnt effect comp. test at all. It is probaly carbon build up on the pistons I've seen it before, and maybe a thinner head gasket or hi comp pistons. If it is high mileage its the carbon, and I am a Honda cert. mechanic (Kawasaki too)

 

As the others have said, it's probably carbon build up, but it's also a good possibilty that your compression gauge may be off a little. The main thing on a compression test is close numbers. As long as yourcylinders are within 2%~3% of each other, and in the neighborhood of what they should be, you're OK. [8D]

 

I'd be grateful and not question it, haha.