1982 Johnson 25hp - NEED EXPERT ADVICE

[sah440]

When I turn my ignition key the motor runs for a few seconds, backfires, then stalls out. I know that this is a fuel delivery issue but I am not sure where the problem exists.

This is what I do know:

1) Only 1 cylinder is running. While servicing the motor I accidentally broke a wire in the coil assembly - therefore there is no power going to the upper spark plug. Replacement part is on the way. I'm not sure if this could cause the problem. Proir to this accident spark was present in both cylinders.

2) I removed the carb and thoroughly cleaned it. Had a carb kit in hand but did not even need to replace any parts.

3) I pressurized the fuel line using the in-line bulb. I could hear the reservoir in the carb fill with fuel as i squeezed the bulb. When the reservoir was full the bulb became very firm as expected. I inspected all visible fuel lines and found no leaks.

4) The fuel filter is clean as a whistle, fuel pump did not leak under pressure.

5) Pulling/releasing the choke has no effect.

6) All wiring and spark plugs are NEW.

7) Both cylinders are getting 120psi and it holds after compression had stopped

This is what I know about the problem. Any additional insight would be appreciated.
Thanks,

Scott

 

[Cofe]

Re: 1982 Johnson 25hp - NEED EXPERT ADVICE

Initial low speed needle setting is 1-1/2 turns out. A lean condition can cause the backfire. It could also be a sheared flywheel key, this can cause a backfire.
I don't think you will be able to trouble shoot very well until you get your new coil.

 

[HighTrim]

Re: 1982 Johnson 25hp - NEED EXPERT ADVICE

Where did the wire break, and is now taped off or is it arcing around?

Is it a mild backfire, or more of a shotgun going off type sound?

 

[sah440]

Re: 1982 Johnson 25hp - NEED EXPERT ADVICE

Initial low speed needle setting is 1-1/2 turns out. A lean condition can cause the backfire. It could also be a sheared flywheel key, this can cause a backfire.
I don't think you will be able to trouble shoot very well until you get your new coil.

Can you or anyone else elaborate on the initial low speed/lean condition.... or flywheel key???

This is my first project motor and I have really come a long way with it. I knew absolutely nothing when I started and at this point I ALMOST have it running. So im just learning little by little... I not sure what those terms mean.

 

[sah440]

Re: 1982 Johnson 25hp - NEED EXPERT ADVICE

Where did the wire break, and is now taped off or is it arcing around?

Is it a mild backfire, or more of a shotgun going off type sound?

The wire sheared right where it enters the could assembly molding, therefore I cannot repair it but i found a cheap replacement. The wire is now taped off.

The backfire is not that loud. It sounds as it should when it runs, the pops rather quietly (as I have heard some as loud as shotguns), it puffs out a bit of smoke as it stalls.

 

[Cofe]

Re: 1982 Johnson 25hp - NEED EXPERT ADVICE

That thumb screw needle on the front of your carb is the low speed idle fuel/air mixture setting. If the motor is not getting enough fuel,(lean condition) it will backfire. Start with that screw turned 1 1/2 turn out. If it still backfires open it a little more until the backfire stops

 

[sah440]

Re: 1982 Johnson 25hp - NEED EXPERT ADVICE

That thumb screw needle on the front of your carb is the low speed idle fuel/air mixture setting. If the motor is not getting enough fuel,(lean condition) it will backfire. Start with that screw turned 1 1/2 turn out. If it still backfires open it a little more until the backfire stops

Thats what I thought. I attempted ignition at every one turn interval from low all the way up to high. Im not getting a backfire every single time, maybe 40%. And im pretty sure it happened at low and high.

 

[HighTrim]

Re: 1982 Johnson 25hp - NEED EXPERT ADVICE

Disregard the numbers on the dial for now.

As cofe stated, lightly turn the dial clockwise until it bottoms out. DO NOT over tighten. Then turn Counterclockwise exactly 1.5 turns. From there it is fine tuning on the water, turning in small increments, see the FAQ for a thread by Joe Reeves for this when you are ready.

But as stated, dont even bother with this until the coil is installed and you have good spark on both cylinders. Once the spark is present, compression is good, is it time to fine tune fuel delivery.