compression on 79 Johnson 150hp

[rlouis5]

I have a 1979 150hp Johnson motor that seems to start and run well on a stand BUT it only has 90# of compression on each cylinder...Is that too LOW??? also this motor seems to run smooth and accelerates quickly but will die and then not start again until it seems to cool down then it will start right up again and repeat this process..it usually will run for about 3-4 minutes before it just seems to run out of fuel... any help will be apreciated..thanks in advance
Robert

 

[JB]

Re: compression on 79 Johnson 150hp

90PSI is fine for that engine, Robert. Those big V6s were made with low compression.

Sounds like you may have a heat failure in your ignition system or a fuel delivery problem in which the fuel pump cannot keep up with fuel usage at WOT.

Check for proper ventilation of your fuel tank and possible air leaks in the fuel lines. A failing fuel pump can also cause that sort of problem.

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[rlouis5]

Re: compression on 79 Johnson 150hp

How can I check for heat failure in the ignition system? not cooling system? I have checked for leaks in the fuel system and replaced all hoses and the prime bulb and still have the same problem...I will check the fuel pump...thank you soooooo much
Robert

 

[JB]

Re: compression on 79 Johnson 150hp

I have found heat failing parts by heating them with a hair dryer, Robert. Put her on the muffs at idle and blow hot air into the ignition system. Might work, might not.