1983 johnson 15hp wont run.

humboldtbrad · Sep 9, 2013

ok so to start some back story I have horrible luck with ob's.
I bought this one it ran like a champ its been well maintained at a local shop. I took it out and ran it for 4 hrs on humboldt bay without any issues (31mph according to gps) on my 12' valco.
4 days later i took it to the lake and put it in the water loaded up and took off i got 1/4mile (maybe) and it died (it sounded like it was running rough) and it wouldn't restart.
i got it home checked spark and compression (75psi equal if memory serves) tried starting it again and could only get it going at wot then it would die after 10 sec

Whats wrong with it?

boobie · Sep 9, 2013

Re: 1983 johnson 15hp wont run.

How did you check your spark ?? You should be using an open air gap tester set at 7/16".

Riverrat47274 · Sep 9, 2013

Re: 1983 johnson 15hp wont run.

If the motor has set before you got it carb may need rebuilt.ive got the same motor and am having the same problem(won't run at wot)

humboldtbrad · Sep 9, 2013

Re: 1983 johnson 15hp wont run.

it will run at wot (in nuteral) and thats it. carb rebuild huh sounds like fun.
gap was 1/4 inch so its good

humboldtbrad · Sep 9, 2013

Re: 1983 johnson 15hp wont run.

whats standard compression on these motors

Daviet · Sep 9, 2013

Re: 1983 johnson 15hp wont run.

They don't list a compression spec on outboards. If you have 70-80 psi on a rope start, and each cylinder is within 10% of each other, it should be enough to start the engine.
Don't run your engine above a high idle without a load on it, might end up with a runaway, then you end up with pieces instead of an engine.
It sounds like it might be time to overhaul the carb, make sure you remove the high speed orifice and make sure it is clean.

humboldtbrad · Sep 19, 2013

Re: 1983 johnson 15hp wont run.

so i rebuilt my carb and it fires up fine in neutral when its against the neutral throttle stop but if i take it off that even to the start position it dies. so i was looking at the throttle ramp and the little wheel that rides on it moves literally less than 1/64" to go from screaming to dead. the ramp looks worn. i cant figure out how to adjust my idle my ob has the lean rich adjust and a knob on the side which is froze and i cant do anything with it but it doesn't seem to have anything to do with the carb
im just having a hard time with it

AlTn · Sep 19, 2013

Re: 1983 johnson 15hp wont run.

if you haven't done so already ..google leroy's ramblings..and study his writings on repair and maintenance of the omc 9.9/15 hp. series..as well, I think there are a couple of utube vid's on the carb rebuild and setting...the carb work is dependent on verifying that the spark will jump a 7/16" air gap and will pass a cylinder drop test while running

bonzoscott · Sep 19, 2013

Re: 1983 johnson 15hp wont run.

humboldtbrad said:
so i rebuilt my carb and it fires up fine in neutral when its against the neutral throttle stop but if i take it off that even to the start position it dies. so i was looking at the throttle ramp and the little wheel that rides on it moves literally less than 1/64" to go from screaming to dead. the ramp looks worn. i cant figure out how to adjust my idle my ob has the lean rich adjust and a knob on the side which is froze and i cant do anything with it but it doesn't seem to have anything to do with the carb
im just having a hard time with it

The ramp and the roller is your timing advance and does play a big part. You state the ramp looks worn, but can't see that happening. Do you mean the roller? If it has worn a groove in it, may very well be your problem. Try and get it running, stick the tip of your thumb on top of the roller and move it ever so slightly forward. If she straightens up, then try and wrap a tiny piece of duct tape all the way around the cam roller surface and see what happens. If she straightens up, get a new roller. The Ramp (Cam) is adjustable BTW.

humboldtbrad · Dec 5, 2013

Re: 1983 johnson 15hp wont run.

Its been a while but I got frustrated and gave up so now I have more time and I'm back at it 10 min ago I fired it up and still the same problem I verified that I have good spark 1/2" using the tool.
Then I did a drop test and it is only rinning on the top cyl I pull off the lower spark plug wire and no change at all. Then I pull the top one and it dies.so now what does the problem sound like? Also I get gas/oil mix pooling around the base of the motor

tomhath · Dec 5, 2013

Re: 1983 johnson 15hp wont run.

Make sure you have the correct spark plugs, most used motors will have the wrong plugs because the previous owner stuck in whatever he had on hand.

What do you mean "pooling around the base of the motor"? At the top near the powerhead? Sounds like you might have a leaky fuel line or stuck float in the carburetor. Neither is a big deal to fix, just look around to find where it's coming from.

That knob on the side is used to limit the throttle to set the idle speed, keeps it from going too low. There's a set screw that needs to be loosened before you can turn it.

The cam that the little roller rides on can be adjusted but you need instructions.

Bottom line is that you really need a service manual; those motors are easy to keep running but you can't do it without a manual.

AlTn · Dec 5, 2013

Re: 1983 johnson 15hp wont run.

I'd suggest you swap the plugs and verify that the lower plug is working properly; it'll fire in the top cylinder. If the lower plug is oil fouled you may have a hole in the fuel pump diaphram and it's leaking from the back into the lower cylinder < if this is where it gets its pulse from>. You can take the fuel pump off the block leaving the fuel line from the tank attached. Remove the fuel line that goes to the carb and while you block the outlet to the carb, pump the primer bulb from the tank and determine whether the f/p is leaking.

Your fuel pooling could come the carb, hole in the fuel line, bad fuel connection, crankcase half leak, f/p leaking,etc. I'd suggest you clean it as best you can and inspect carefully.

Post back if your ignition problem isn't from a fouled plug as there are other "avenues to explore."

pn · Dec 9, 2013

Re: 1983 johnson 15hp wont run.

and the solution is...

humboldtbrad · Dec 24, 2013

Re: 1983 johnson 15hp wont run.

Well it turns out I lost a rod through the side of the block
toasted

boobie · Dec 25, 2013

Re: 1983 johnson 15hp wont run.

Now that Sucks !!

bonzoscott · Dec 25, 2013

Re: 1983 johnson 15hp wont run.

Probably result of running it at WOT in neutral.

1983 johnson 15hp wont run.

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