20hp Johnson Running Bad

Lilpub

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Joined
Apr 24, 2007
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2
I have a 88 11' boston whaler sport with a 88 johnson 20, I am having a problem with the motor that I can't seem to get straight. When you first fire the motor it fires fine and runs ok, at least the same as it has for the past 5 years. The problem begins when you go above idle, and is much worse with more weight in the boat. You hit the throttle and it bogs a little but eventually gets up on plane and then goes great for about 3-5 minutes then it starts to cut out dramatically. The only way I can keep it running is if I hold in the choke on the key, as soon as I let that go it cuts out, but as soon as I push it in it goes again. Changed the plugs but no help. Thinking its a fuel problem because of the choke helping it run. Here are some things that I did notice, the primer ball never seems to get completley firm, and there are a couple of fuel lines at the motor that don't have clamps on them at all. Obviously I plan on at least putting zip ties on these for safety, and could they be allowing the pump to loose suction, and cause the motor cut out, and the soft primer? Checked compression and it is fiine on both cylinders. Any suggestions would be greatly appreciated on this problem as I move forward.
 

wbeaton

Commander
Joined
Jul 30, 2006
Messages
2,332
Re: 20hp Johnson Running Bad

Do you have the tank vent open? When did it last run fine? Did you stabilise the fuel before storage? Could be you have some crud in your carb.

Those fuels lines are probably fine. There isn't a lot of pressure in them. My 1987 20 hp only has zip ties. The bulb never gets hard and the line from the tank has very little fuel flowing through it at WOT (I can see it through my glass inline fuel filter).
 

Lilpub

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Apr 24, 2007
Messages
2
Re: 20hp Johnson Running Bad

Tank Vent is open, Stabalized Fuel before storage and it ran ok last summer. I have run 3 tanks of fuel through it as is (18gallons)beleaving it was the old fuel but the problem is still there. Thanks for the input, sounds like i'm on the right track.
 

tashasdaddy

Honorary Moderator Emeritus
Joined
Nov 11, 2005
Messages
51,019
Re: 20hp Johnson Running Bad

choking is adding fuel to keep it running, either air leaks, bad fuel pump, or dirty high speed jets,. or sticking float, not letting in enough gas. also by choking you are cutting off the air supply allowing the pistons to help suck more fuel. by bet is on the carb.
 
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