fuel

[GARY STEFFENEY]

had a friend ask me a question and found myself scratching my head,,,, 40hp oil injected johnson will only run with gas cap loosen on gas tank,,, is this fuel pump or where would pressure going into tank come from,,, said when loosens cap shoots air out like compressor in there,,, thank you for any thing you could offer,,,,

[crosbyman]

tank vent plugged up….. it should suck in fresh air as fuel gets pumped out

air pressure build up indicates no venting……. check fuel cap vent or tank /overflow vent

Joining AOMCI has priviledges 🙂

[GARY STEFFENEY]

thank you i was sorta leaning that way,,, the cap is probabliy the problem as the pin hole is plugged , is that what i hearing,,

[fleetwin]

OK, perhaps the hissing you are hearing is air being sucked into the tank…Having excess pressure in the tank would not stop the engine from running, unless the carbs are actually flooding over…Many of these tanks have just a one way vent, into the tank only….

[outbdnut2]

You said “oil injected”. DO you mean the infamous 6 gallon tank where the oil goes in a different cap to a separate container in the tank? If that’s what your friend has, the oil is supposed to mix with the gas as it comes out of the tank. These were made in the late 1980s. They are notorious for the low oil sensing mechanism shutting off the gas when the oil it still nearly full, leaving you stranded…..but that’s not the problem you described. I just mention it to maybe save him from getting stranded. If your friend happens to have one of these tanks that’s still working, I wouldn’t trust it. I had one new in 1989 and one year later it stranded me on the lake. I took the tank apart and got rid of the mixing stuff and drilled 1/4 inch holes in the oil reservour so it will fill with gas, then I just mixed oil with the gas like any other motor.
Dave

[GARY STEFFENEY]

thank you for the great info i will relay it to him as i’m not sure of tank he has but now can check,,,,,,

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