Fuel Problem w/ 1991 Johnson 70

[agonzales1981]

Just got this boat/motor from a guy who hadn't fished it in about 3 years, motor was super super clean but wouldn't start of course. Cleaned (did not soak) carbs, top carb was really gummed up, the middle and bottom weren't bad at all. New floats and needles. New NGK spark plugs. New water pump. Wasn't sure on the adjusment for the carbs, but they were opened about 2.5 turns. Put her in the water, and it seems like it will only start w/ the rev handle (not sure proper term) up about halfway and when the handle is down sometimes it will cut off and I have to start it up again w/ handle up. Got it going and put the throttle all the way down and seems like it isn't getting enough fuel, motor sounds smooth and everything, no popping or coughing but the motor is obviously not putting out full power. Where should I start?

 

[agonzales1981]

Re: Fuel Problem w/ 1991 Johnson 70

Forgot to mention it is an older metal omc tank and the cap is not vented.

 

[agonzales1981]

Re: Fuel Problem w/ 1991 Johnson 70

bump

 

[snowseeker]

Re: Fuel Problem w/ 1991 Johnson 70

When cold you will need to leave the warm up lever "rev lever" up around 2000rpm for around 2-5 minutes to get the motor warmed up enough to where it will idle on its own with the lever down.

Honestly I would just take the boat out and run a tank of gas threw the motor and see if it clears up or how it acts. After sitting so long sometimes all a motor needs is to be ran for awhile to clear everything out and get everything working and moving like it should again.

 

[1946Zephyr]

Re: Fuel Problem w/ 1991 Johnson 70

What is the purpose of the "bump"?

 

[agonzales1981]

Re: Fuel Problem w/ 1991 Johnson 70

Thank you for the reply. Also I pulled the plugs and the bottom 2 looked similar w/ a light oil mist around threads and dark brown color to them. The top plug looked brand new still, no oil on the threads at all.

 

[agonzales1981]

Re: Fuel Problem w/ 1991 Johnson 70

Also, on one of the carbs that we rebuilt the needle (little part attatched to the float) I think it's called got stuck down a few times instead of popping up when the float did, we tapped it and it seemed to be working could this maybe be causing this top carb to flood and this is why the threads on the plug look so clean? I hope it's not some kind of head gasket problem or worse, motor looks to be in too good of shape for that!

 

[agonzales1981]

Re: Fuel Problem w/ 1991 Johnson 70

update,

checked compression, 118 118 120 while cold

checked spark and all had good spark.

Pulled the top carb (the one that was really dirty) the jet in the float chamber had a lot of gunk still, gooey old oil. Also, when we first cleaned this one last week we tried to get the jet out and couldn't and it was stripped. Could this be the problem?

 

[agonzales1981]

Re: Fuel Problem w/ 1991 Johnson 70

I appreciate all the helpful replies

 

[Silvertip]

Re: Fuel Problem w/ 1991 Johnson 70

The plug that is looking like new is the cylinder and carb with the problem. Good plugs and proper mixture settings provide a slight tan/brown plug color. White is a non-functioning cylinder which also accounts for poor idle. It also means the engine is vibrating and not running smooth. Fix the carb. That cylinder not getting fuel also means it is not being lubricated which also means if you continue to do what your doing you will be looking for engine overhaul information.

 

[agonzales1981]

Re: Fuel Problem w/ 1991 Johnson 70

The plug that is looking like new is the cylinder and carb with the problem. Good plugs and proper mixture settings provide a slight tan/brown plug color. White is a non-functioning cylinder which also accounts for poor idle. It also means the engine is vibrating and not running smooth. Fix the carb. That cylinder not getting fuel also means it is not being lubricated which also means if you continue to do what your doing you will be looking for engine overhaul information.

I pulled the carb last night and the jet in the lower bowl portion was all gunked up w/ slimy oil, the jet was stripped so I got it out of there and cleaned it all real good and ordered a new jet. The old jet was about half full of old hardened oil when I got it out of there. I think this was the problem.