1988 15HP Johnson...

Hey guys, looking for some information about this motor. I'm trying to figure out what the black knob is to the right of the choke lever. Looks like either an idle or mixture knob.

My brother just recently bought this motor from a friend of mine, who bought it from a guy who rebuilds and restores outboards. It has excellent compression, all new ignition system and rebuilt carb. My buddy never used the motor, he just had it in the garage as a spare, so he had no idea what the black knob was for.

Well this morning my brother was going hunting and started the motor at the ramp. It started in 2 pulls, but then it quit running. He ended up having my Dad tow him out to a spot, but he still can't get it to restart. I'm not there to troubleshoot, but what I'm looking for is a starting procedure with this motor.

I was an outboard technician in the Coast Guard on the larger Johnson and Honda motors and I've rebuilt several smaller mercury engines. I've never worked on anything this old, so I really don't know what position that black knob is supposed to be in, but I can tell you from the time I test ran it, that the position of that black knob is the difference between the engine running and the engine not.

Thanks

Re: 1988 15HP Johnson...

That knob adjusts the idle mixture. Pump fuel bulb till hard, set throttle to the start position, pull the choke out and pull it over. Once it is warmed up enough to run push the choke lever in. Idle adjustment should be done in the water, if it's too lean or rich you will hear it, it won't run well.

Re: 1988 15HP Johnson...

Airdale; I can tell you from the time I test ran it said:

Actually, that knob has no bearing on starting or running above idle. That is your low speed jet and it only affects low speed running. Factory setting for the jet is 1-1.5 turns out from gently seated. Tweak as necessary once the motor is up to normal operating temperature.

To start the motor, connect the fuel line. Open the tank vent. Make sure the fuel line is connected in the correct direction of flow. Pump the fuel bulb until firm. Pull out the choke knob and pull the starter rope until the motor attempts to start. Once it fires push the choke back in. It may not run after it first tries to fire, but that's normal. Pull the starter again and it should start. It doesn't usually take more than a few pulls.

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Re: 1988 15HP Johnson...

Two links for you to look at

Firstly Joe Reeves instructions for adjusting carb mixture needles http://forums.iboats.com/showthread.php?t=167352

Secondly for practically everything you need to know about 9.9 and 15hp engines http://forums.iboats.com/showthread.php?t=158087


When/if the idle mixture is correctly adjusted the knob will be set in the middle of its range and should not normally need touching.
I do find it helpful though to turn it counterclockwise to make the mixture richer while the engine warms up rather than try to set the choke to a partially open/partially closed position. Experience will show if that is necessary or even helpful.

Re: 1988 15HP Johnson...

Vic.S said:

I do find it helpful though to turn it counterclockwise to make the mixture richer while the engine warms up rather than try to set the choke to a partially open/partially closed position. Experience will show if that is necessary or even helpful.

Click to expand...

That is a good point. All motors have their quirks. Some will start easier than others. I find it rare that these motors need extra choke at start up, but I have encountered it before.

While you are trying to figure out your particular starting procedure you may find that you are flooding the engine. If this happens, I find it best to remove the fuel line, push the choke in, turn the throttle handle all the open while still in nuetral and pull the starter until it starts and runs. It'll be a little rough running until it burns through the extra gas. Plug the fuel line back in after it starts to run better. This may take a few seconds.

Re: 1988 15HP Johnson...

Thanks for the replies folks.

Well I just talked to him and they're still out there. He tried starting it again with no luck.

Here's the details he gave me -

This morning at the boat ramp, he started the motor in the parking lot to make sure it would fire up, it fired up on 2 pulls with the choke out, then he pushed the kill button in to shut it down.

He launched the boat, and then went to start it again. Won't start. He said it doesn't even sound like it wants to start. To me, this is a classic kill switch interrupt. If the motor was running fine prior to shutting off with the kill button, and now it doesn't even smoke or kick like it wants to start, I'm thinking the kill button shorted out.

I don't know these Johnsons, but on all the Mercs I've worked on, there are two wires coming out of the tiller handle, I told him to find those wires and trace them to the ignition, then disconnect them. Unless Johnson runs some sort of backwards wiring, by disconnecting the kill switch it should restore power to the ignition when he pulls it. My understand is that kill switches, when engage, create an electrical ground circuit that cuts out the ignition. If he disconnects the kill switch, it should run.

He couldn't pull the plugs out on the water because they don't have the spark plug wrench that fits. But based on what he is telling me, the motor has no indication that it is getting spark. Fuel seems to be okay, but no spark.

Re: 1988 15HP Johnson...

First, tell him to never start it out of water again. The water pump impeller is rubber and will be damaged if he runs it out of water. Second, motors with low compression often run out of water when there is no load, but will not run when underload (in water). Check compression. You want over 90 psi and within 10% of each other. I don't know how low the compression can be and still run in that motor. Of course, since you say you had it running once in water compression probably isn't the problem, but you need to rule it out.

Check for spark. Use an inline tester or make the spark jump a 1/4". Testing spark by placing the electrode against the block won't tell you much. The fact that he started it and killed it with the switch twice suggests that the kill switch is ok. However, you can disconnect it to rule it out. It works the same as a Merc kill switch. I believe one wire is grounded on the block at the back by the cylinder head and the other goes up under the magneto.

If the motor was stored a long time before use then there could be some varnish in the carb.