I recently checked my stock 03 400ex with a compression gauge and got a reading of 70-75 psi. Is this good or does it need some help? What should the compression be? Thanks.

 

it should be bvetween 100-128 psi

 

Also, make sure you hold the throttle wide open when checking the compression, otherwise you could get false readings.

BTW my compression tester only has fittings for the two common automotive sized plugs. Anyone know who carries just the fittings or adapters that will fit the EX?

 

Be aware also that some engines have decompressors, to aid in hot starts. If your engine has one of these, you will need to do the type of test where air is pumped into the combustion chamber under pressure, and you wait to see if it holds (rather than cranking the starter or kicking it over).

 

i believe mine is sun-pro. got it at pep boys as a kit for 40 buks. you can probaly just order the adapter your after. maybe search it online.

 

"Be aware also that some engines have decompressors, to aid in hot starts. If your engine has one of these, you will need to do the type of test where air is pumped into the combustion chamber under pressure, and you wait to see if it holds (rather than cranking the starter or kicking it over). "

Or disconnect the decompressor cable like I have to do with my 250X.