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Used old gas in Johnson Outboard

D

d3washburn

New member
I think I used some old gas in my 135 hp Johnson Outboard motor, and now it will not idle down enough to shift it into gear without killing the engine.

What do you recommend I do to fix this problem and get my motor running good again?

Yes I already drained all the old gas out, and put new fresh gas in the tank.

I tried the following without a lot of success.
Put new spark plugs in.
Sprayed brake free lubricant, and cleaner into the cylinders when spark plugs were out.
Got a couple of gallons of new gas in a portable tank and added one oz of marine sta-bil and 5 oz of sea foam.
Checked and cleaned all the fuel filters and screens.
Got the motor started at home with the muffs on and run about a gallon of the fuel through it. Got a lot of smoke and a lot of gunk (old black oil) come out of the exhaust
Still running very rough, and would stop if I tried to idle it down.

Now what do I try?
 
The 1973 models are a " one off " year.------Few powerhead parts from 72 fit and very few parts from 74 fit it.----A major problem was broken piston rings. You might want to start with a compression test in this case.-I can only suggest that you start this way.
 
I don't think the old gas is the problem, unless you left some in the carbs, in which case you need to tear them apart completely and properly clean them. I would do the compression test and spark test first to make sure you don't have a bigger problem before tearing down the carbs.
 
Agree with compression test and leak down test. If low compression, I would do a decarb - 1 part Sea Foam to 3 parts gas. Run it for about 5 to 10 minutes on muffs, or until it stalls out. Then let it sit for 30 minutes. Then run it on straight gas for 10 minutes. Then repeat with Sea Foam. Then do compression test again. This will lean the cabs and clean out carbon build on rings and valves.
 
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