Mercuiser 165 Stops When Hot

Hi. I have a 1978 Mercruiser 165 which is running really well except for one problem. After about 20 minutes of running the engine starts to miss and then eventually dies. I have recently overhauled the cooling system replacing the exhaust manifold and elbow and the lower water pump impeller as well as the thermostat. The engine is not overheating in any way that I can determine, the gauge is fine, there is plenty of water flow, and the engine is not getting excessively hot. If I leave the motor for about five minutes then I can restart and carry on but then 10 minutes later the same problem happens. Could this be fuel boiling in the fuel bowl and venting directly to the carburettor and flooding the engine with fuel? My fuel bowl is 100% full and there is no sign of water or any other contaminants. Should the bowl be that full?

 

What do the spark plugs look like?

 

i know this will sound funny but did you check the new exhaust manifold for things in it

this happens on cars a lot when the exhaust system gets plugged


run for a little while and stop the sit for a while then run great for a little while then stop etc etc

let me know

thanks

 

Sounds very much like a crack in the block. once the engine gets hot enogh the crack will open and allow small dropletts of water in. You may need to get each chamber stained and machined to see if their is a crack.

Stu