Low compession 1979 merc 150 outboard

[harnessedenergy06]

Hi everyone, I am looking at a motor to replace or use parts for my other merc. Sounds funny I know. This motor I am looking at has compression in 1,3,5 of 97psi all the same. 2,4,6 are at 67psi all the same. What is the compression of a rebuilt one(around 120-150psi?) What would cause this? My friend would give it to me for free. Wondering if it will start. Getting a key for it tomorrow. Free and gets me on the lake. Always hoping for the best! Thanks Energy

 

[cyclops2]

If someone has the old specs about the compression ratio. Then just multiply the compression ratio buy 14. Close enough for repair work. At that age you could have 2 DIFFERENT compression ratio heads......................ONLY use ..............non Ethanol gasoline............Assume Ethanol has been used & damaged some fuel system parts. Pump diaphram, float, fuel line, bulb......etc.

 

[faztbullet]

What is the compression of a rebuilt one(around 120-150psi?)

That motor has the 'hemi" head chambers and compression new was about 135psi and below 100psi its going to have problems running.

What would cause this?

worn out or damaged cylinders....

 

[cyclops2]

Can the reed leaves be set wrong ? then they will leak compression pressure.........anyting is possible after any repair job.

 

[fastjeff]

I assume that's a V-6? One bank may have been starved for water and burn up.

Reeds have little to do with cylinder pressure.

Jeff