Expert: tyler boehner - 2/9/2008

Question
Jeff,

Just had a Mercury Mechanic check my 1992 60 engine compression. Reading were Cylinder 1 - 135 psi, Cylinder 3, 130 psi, Cylinder 2- 30 psi The motor started up and ran fine with the muffs.

Do you think it would be worth while to spray decarb in that cylinder to see if there is a remote possibility that I have a stuck ring. If so what is the procedure.

Thanks in advance.

Joe

Answer
Compression on a two stoke can be useful but at the same time can hide the truth.  Best test to run is a leak down test on each cylinder.  If your tech doesn't know what that is, find a knew tech.  The test shows how much pressure the cylinder can hold at top dead center.  If you have a bad cylinder you will know after that test.  It might sound like it runs fine on the muffs, but don't be fooled.  If you are missing or running weak on #3 you probably can't tell running it in a test tank or on the muffs.  You have to put the motor under a heavy load.  Run the leak down test.  Sorry, but you probably need to hone a cylinder and replace your rings or get a rebuild.