compression issue

[tiller man]

tohatsu 18 hp 4 stroke no compression top cylinder. could this be a sticking valve. when running sounds like it fires ocassionally.

 

[racerone]

Remove valve cover and observe operation of valves.

 

[tiller man]

Remove valve cover and observe operation of valves.

with the engine running or turn over by hand. Pull start.

 

[tiller man]

by the way thanks for responding.

 

[MattFL]

By pulling the rope. Start by making sure they're all moving and no parts appear to be bent or missing, then check the clearances against spec. The clearance info is sometimes on a label on some motors, or it will be in the service manual for sure. Also take a look at the spark plug and look for anything unusual. Is the electrode missing or damaged, is the spark plug shiny and clean or rusty (indicating a water leak into the cylinder), etc..

 

[pvanv]

Could be a lot of things. Do a leak down test and check by cranking as matt suggested.