Topic: 1985 Johnson 8hp running rough – Antique Outboard Motor Club,Inc

This topic has 16 replies, 8 voices, and was last updated 7 years ago by davesko.

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April 16, 2018 at 3:53 am #9655
davesko
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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
April 16, 2018 at 4:23 am #74108
Mumbles
Participant
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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April 16, 2018 at 4:41 am #74109
davesko
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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.
April 16, 2018 at 5:35 am #74112
PugetSoundBoater
Participant
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.

"Some people want to know how a watch works, others just want to know what time it is"
Robbie Robertson
April 16, 2018 at 11:58 am #74115
crosbyman
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Canada Member
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

Joining AOMCI has priviledges 🙂
April 16, 2018 at 3:58 pm #74121
john8504
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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.
April 16, 2018 at 4:04 pm #74122
fisherman6
Participant
US Member
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

OldJohnnyRude on YouTube
April 16, 2018 at 5:20 pm #74125
davesko
Participant
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.
April 16, 2018 at 5:35 pm #74127
Mumbles
Participant
quote davesko:

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.
April 16, 2018 at 6:13 pm #74132
davesko
Participant
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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