1978 15 HP Johnson that won't idle at low speed

[111torrance111]

I have a 1978 15 HP Johnson that won't idle at low speed and dies when you put it in gear. The motor will start right up every time and will idle fast, but when I reduce the idle speed it will die & also if I put it in gear it will die. At fast idle the motor sound good, I checked the compression and it has 110 LBS in both cylinders. If I leave it as a fast idle it will stay running until I turn it off so I assume there's no fuel issue. The gas seems ok, I haven't changed the sparks plug yet. I have a manual & it seems like I checked everything, so I must be missing something simple. Please help with the proper tune up procedure, I removed the flywheel and didn't see any points so I assume I'm missing something. History: When I got the motor it was frozen, I removed the plugs and oiled the cylinder, it came loose pretty easy. The started didn't work so I rewired it and was now getting good voltage to the started but still wouldn't work. I took it off cleaned it the brushes and contact and reassembled. Worked great. Any help would be appreciated. Jerry

 

[flyingscott]

Have you thoroughly cleaned the carb and put a good rebuild kit in it? You also need to check for spark on both cylinders needs to jump a 7/16" gap. It sounds like the motor sat for a while unused.

 

[oldboat1]

^^good advice. You might get it to idle by removing the idle needle and spraying thoroughly with carb cleaner, using the plastic nozzle. Get the spray way back up in there. If it's responsive to needle adjustment (and wasn't before), you've made progress. If it's unresponsive, you need to open up the top and clean -- check for blockages, including the broken point of a needle. Initial setting is 1 1/2 turns counterclockwise from light seat. Motor should start and run, subject to further adjustment.

 

[111torrance111]

Thanks Flying Scott & Oldboat 1:

I did remove and clean the carburetor, the float and everything seemed ok. When I first ran the carburetor cleaner down the idle hole it seem like it was clogged a little, did it a few times and all 3 small hole seem to be spraying equally.
The fuel line from the pump to the Carb. seem pinched, I replaced and rerouted.

Reassembled, started with new fresh gas/oil. The old plugs didn't look that great so I cleaned them up and reused.

The motor started just fine with some improvements. Although it idles a little better it's still not right, but now when I put it in gear it will stay running at higher RPM. If I bring the speed down while in gear she still wants to die.
I rechecked the compression after letter her run a while and now it read 130 LBS per cylinder.

I guess I'm at the fine tuning stage but don't know what else to do, I'm reading the manual but just can't see how to work this out.

Just to confirm, this motor doesn't have a set of point anywhere that I can see. Correct?

Thanks for help, it improving just not ready for the water yet.

Jerry

 

[racerone]

No points of any kind on that motor.---Is the motor warming up ?----Thermostat installed and working properly ?

 

[tomhath]

Sound like it's either running really lean (most likely), or the timing is way too advanced.

A carb rebuild kit is cheap and easy to install. Then search for how to do a "synch and link" to get the spark advance correct.

 

[Tim Frank]

I guess I'm at the fine tuning stage but don't know what else to do, I'm reading the manual but just can't see how to work this out.

Just to confirm, this motor doesn't have a set of point anywhere that I can see. Correct?

Thanks for help, it improving just not ready for the water yet.

Jerry

Exactly what manual do you have? It should show you the entire ignition system and there are no breaker points.
What plugs are you using?

 

[racerone]

Checked reed valves ?----Checked lower crankcase seal ?---Does spark jump a gap of 7/16", yes or no ??---Checked thermostat, yes or no ?

 

[dazk14]

Let's go back to the basics. Great job ensuring the 3 small holes are clear, they clog easily. 130psi is actually too high if gauge is accurate, so I'm guessing your rich and leaving lots of oil in the cylinder, unless you're over oiling on purpose, which isn't a bad idea.

When it stalls out, will it restart without choke, just more throttle...which is classic rich condition.

Warm the motor up for a few minutes. lower the idle speed, but keep it running. rotate the mixture knob clockwise and see if rpms go up. If so lower the speed to keep it running keep leaning until rpms start to drop or spits back. make a note of needle position. Back needle out 1/2 turn and do same counterclockwise until rpms start to drop.
Generally in between the lean or(spits back) and too rich (wants to slow and die) is about right. you may need to pull off knob to get past stop.

Put in tank, Put in gear and dial in by sound the best idle. Slightly rich is better than slightly lean. pull mixture knob off and replace so pointer is pointed down.