1987 Johnson 6hp, only runs for a few seconds?

Hey all, I'm hoping someone on this forum can help me out.

I have an 1987 Johnson 6hp that I can't seem to get to run for more than a few seconds.

I've ruled out the fuel pump, and cleaned/rebuilt the carb (twice), new plugs.

Symptoms:
Starts easily, but shuts off after about 5-15 seconds
Can be made to stay on longer if I carefully rev up and down.
Throttle response is extremely sluggish

Basically the motor runs like it has the choke stuck out, but this carb doesn't have a choke, or even a high speed needle. Low speed us turned 1.5 turns out.

Any ideas?

Welcome aboard. In order to restart do you have to choke or prime it? Alternatively.... If it seems it's flooding at low speed, it could be the main fuel pump diaphragm.

timguy said:

Welcome aboard. In order to restart do you have to choke or prime it? Alternatively.... If it seems it's flooding at low speed, it could be the main fuel pump diaphragm.

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There is no choke on this carb, just a primer (maybe serves both purposes). I need to prime before every restart. It's almost as if it's only running off of the fuel from the primer--although I can keep it running at high revs for a few minutes as long as I feather the throttle--so fuel is getting into the carb at higher throttle.

I rebuilt the fuel pump, and it works fine. This small motor should run for 30 seconds or more off of just what's in the bowl.

compression is good 110 in both cylinders

That is certainly fine compression for a six horse. Does that model have the wee little tube in the carb bowl area? You must have missed something in the carb that is not allowing administration of fuel at low speed.....gotta revisit this carb very carefully.

timguy said:

That is certainly fine compression for a six horse. Does that model have the wee little tube in the carb bowl area? You must have missed something in the carb that is not allowing administration of fuel at low speed.....gotta revisit this carb very carefully.

Click to expand...

Yeah it has that tube (I replaced it), I suspect that may be where the clog is--the old float was starting to fall apart, so chunks of it may have blocked something.


Going to take one more stab at cleaning the carb then give up. It's not a problem I introduced by rebuilding the carb as it ran identically bad before and after. It was running much better last time I ran it a year ago and ran okay for a few minutes after I took it out of storage, then it started acting up--seems like an obvious carb clog.

I give up... it has all the symptoms of a clogged carb, but I've cleaned this carb out thoroughly 3 times--it's just struggling to suck up fuel. Adjusting the low speed needle has zero effect (unless I screw it all the way in, then I can tell it did something).

Oh well, I guess I'll just watch craigslist for a similar motor that's been abused/seized and pilfer the carb off of it.

Problem may be in top cover (part # 10). Call Tim's Outboard in Hackensack MN at 218 682 2331. They can help you. Have model # handy. They have a kit and probably a good used top cover.....new ones are available but can be very costly if your on a budget. I have covers but for the 9.9/15 hp. You need the smaller cover.

Check spark on every cyl.

timguy said:

Problem may be in top cover (part # 10). Call Tim's Outboard in Hackensack MN at 218 682 2331. They can help you. Have model # handy. They have a kit and probably a good used top cover.....new ones are available but can be very costly if your on a budget. I have covers but for the 9.9/15 hp. You need the smaller cover.

Click to expand...

Thanks! the top cover is the only part on the carb that seems suspect to me. I'll try that number.