1985 Johnson 8hp running rough

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davesko
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1985 Johnson 8hp running rough

Postby davesko » Sun Apr 15, 2018 11:53 pm

Hello all, I have a 1985 Johnson 8hp Motor that has always served me well, I loaned it to a friend and he said took off and ran great for 30 seconds and died off and ran poorly and would barely idle. I ran this motor the previous weekend without issue. I asked him how it ran when pumping the primer bulb and he said it ran perfect. I’m thinking fuel pump but he was using a tank given to him so I’m not sure if that could be the issue. The fuel pump is easy enough to replace and I have a new one but just wanted someone else’s opinion. Thanks in advance. Dave

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Mumbles
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Re: 1985 Johnson 8hp running rough

Postby Mumbles » Mon Apr 16, 2018 12:23 am

The problem could also be in your carburetor. In the bowl.

These carbs have a small fuel line in the bowl which deteriorates and breaks down over time causing all sorts of operating issues. Alcohol in your gas might aggravate the problem. Replacing it with a short length of Tygon will solve the problem.
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davesko
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Re: 1985 Johnson 8hp running rough

Postby davesko » Mon Apr 16, 2018 12:41 am

Hi Mumbles, Thanks for the reply but my carb is not that type on that motor. My 1987 looks like that but the 1985 doesn’t have that tube.

PugetSoundBoater
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Re: 1985 Johnson 8hp running rough

Postby PugetSoundBoater » Mon Apr 16, 2018 1:35 am

What i have done when suspecting the fuel pump is bad or weak, is put a fuel pressure gauge in between the pump and carb. I bought a small Mr. Gasket fuel pressure gauge. I had to put brass step down fittings on the gauge inlet and outlets to match the inside diameter of the fuel line. You will need another length of fuel hose to replace the hose when you are done. You might look for a cracked fuel line or loose connection also.
"We only learn in two ways,one from reading,the other by association with smarter people" Will Rogers

crosbyman
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Re: 1985 Johnson 8hp running rough

Postby crosbyman » Mon Apr 16, 2018 7:58 am

has the fuel filter in the pump screw cap been checked out and cleaned ....after the fuel pick-up it is your first line of defense

easy stuf first !
https://www.ebay.com/itm/Fuel-Pump-3978 ... 100623.m-1

https://www.ebay.com/itm/Fuel-Pump-for- ... gS&vxp=mtr

John8504
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Re: 1985 Johnson 8hp running rough

Postby John8504 » Mon Apr 16, 2018 11:58 am

I've had problems with other engine in the past where it would run horrible and I would have a vacuum leak on one of my lines. Check all the rubber and replace if it's old.
Bringing them back with a little TLC.

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Fisherman6
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Re: 1985 Johnson 8hp running rough

Postby Fisherman6 » Mon Apr 16, 2018 12:04 pm

Have you tried running the motor yourself on your own tank? The problem could be as simple as one or both of his fuel line fittings (depending if the fuel line dis connects from the tank and the motor with a quick connect fitting) has leaky O-rings. It could be drawing air into the fuel line through the fittings and starving the engine for fuel. As mentioned, check the easy stuff first.
-Ben
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davesko
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Re: 1985 Johnson 8hp running rough

Postby davesko » Mon Apr 16, 2018 1:20 pm

Update: Thanks guys for all your suggestions. I took it out this am with my tank and it acted the same way until I took the hood off and it took off and ran perfect. I’m thinking vacuum leak somewhere? I put the hood back on and it started acting up again and stalled and was hard to start, needed the choke! It’s gotta be leaning out.

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Mumbles
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Re: 1985 Johnson 8hp running rough

Postby Mumbles » Mon Apr 16, 2018 1:35 pm

davesko wrote: My 1987 looks like that but the 1985 doesn’t have that tube.



Right you are as your motor should have the normal 9.9 style carb on it. These carbs with the small tube appeared on the '86 models.

davesko
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Re: 1985 Johnson 8hp running rough

Postby davesko » Mon Apr 16, 2018 2:13 pm

Ok so I have it at home now and changed the fuel pump. It revs up in gear, with the hood on freely as much as I can without emptying the barrel, however now when you return to idle it wants to stall, maybe from the hood being on in the barrel? It idles fine with it off. Going to boat test and see what happens


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