Mariner 4hp 60psi!

[Lee1]

Whilst servicing a mariner 4hp sail mate (2005 four stroke) I tested compression and got 60psi! I checked the tester on another outboard and the tester is not faulty! The outboard has a non standard power out modded cable and the outboard owner said he inherited the outboard with a small sailing boat and the outboard powers the boats lights etc so I suspect the outboard has been basically used only as a generator for years, the lower unit, impeller gearbox etc is in a really poor condition but still going after I've serviced it. What's your thoughts on the 60psi? The test was done cold and I will retest it hot and post that psi.

[Lee1]

Resolved! This model has a decompression dump system, some of the compression is dumped to the exhaust whilst starting this is done by a lifter on the cam it's designed to make pull starting easier.