Johnson 1980 70 Hp can't keep it running

phled

Recruit
Joined
Jul 1, 2011
Messages
5
In the process of helping get this old motor back in regular action. It hasn't been started in 15 years. Had the carbs rebuilt twice. New fuel lines, tanks, fuel pump, battery, spark plugs. In the garage on the hose she starts, idles, shift into gear and will run full throttle. Let it run, shut it off, start it up, and it seems fine. I have put in the lake 2 times with the same result. Cold start is typical, but does start, idles and then runs super smooth and fast. The problem comes in when I stop and shut it off for a few minutes. Afterwards it is difficult getting started and then cannot give it any throttle. It will shut down if I attempt to advance the throttle any past slightly more than idle. At 1st I suspected the tanks. They are new Moeller 6 gal tanks that are vented. The instructions for the tanks state to close the vent when transporting and open when in use. The first trip out I left the vent closed and after stopping noticed this and opened the vent. The 2nd trip out I started with the vent open and had the same problem after stopping. Tried vent open vent closed and nothing made any difference. Does anyone have an idea where I should start troubleshooting? I'm stuck. Sorry about the length of this western.
 

soundchaser

Petty Officer 2nd Class
Joined
Dec 8, 2009
Messages
176
Re: Johnson 1980 70 Hp can't keep it running

Check for spark. if one cylinder doesn't have spark, Start switching (coil,CD, timer) wires around until you figure out what works and what doesn't. If you have good spark, Most likely you have the ethenol problem and your fuel lines are falling apart and clogging your main fuel valves in your carbs. You can check the carbs by taking the drain plugs out and pumping the ball to see is you have even flow from all the carb drains.
 
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