69 Mercruiser 120 leak

[taildragger101]

Please help, Just bought a 69 Larson with a 120 Mercruiser. Will run at idle for a short while then start to miss.Ran great at high speed back to idle, run good shortly then start to miss. Pulled plugs and back plug was wet. Turned it over with plugs out and had light water mist out of back cylinder. Pulled the head and really no obvious signs of blown gasket but possible. No water in the oil. Any ideas where to go from here? Thanks for any help

 

[backyard mechanic]

Re: 69 Mercruiser 120 leak

Check your gaskets carefully but it maybe you have a cracked manifold or exhaust elbow. If you have FWC open the cap on the expansion tank and look for bubbles at a fast idle. Tells ya if there is a cracked, broken or bad head gasket. If you left water in the manifold over the winter you might be looking for new parts.

 

[taildragger101]

Re: 69 Mercruiser 120 leak

Heads already off.