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Johnson 70 dies at high RPM

M

maremsk1

New member
Hello all. I have a Johnson 70 hp 2 stroke (early 80s I think). Starts and idles fine, runs slowly fine, but after a few seconds of high rpm usage it stalls or sputters and I have to bring it down to idle again. Im guessing carbs or fuel delivery, but Im not a mechanic so im not sure. Any advice?
 
Some trouble shooting required on your part----------------What are the compression numbers ???-------------Will spark jump a gap of 7/16" on all 3 cylinders ????------Do all 3 carburetors open up properly ( no loose linkages ) ???-------Has the motor sat for any length of time ( possible plugged carburetors ) and have you checked for water in the fuel.-------------Has waterpump been replaced recently ????-----------------Is gear oil clean and no water present ???
 
When under way, have someone constantly pump the fuel primer bulb (acting as a manual fuel pump). If this solves the problem, you either have a fuel/air leak between the fuel pump and the fuel supply OR a failing fuel pump.

What's the model number of that engine?
 
Thanks for the help. Ill have to get that info (im not the one who started the repair). I know comp was tested ok (numbers ???), gas was replaced, spark jumps fine, carbs open fine. The engine has sat for a long time. Maybe 4 months. At first it wouldnt start at all. Then our "mechanic" cleaned the carbs which got it started but now we have a high rpm issue. Now im taking over where he left off. I guess im kind of starting from scratch since im not exactly sure what was done or how well it was done.
 
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