1975 15 hp evinrude 15504C warms up then dies

[KC9000]

Hello and let me thank anyone who has any advice on this topic for your time and advice. This 1975 15 hp evinrude 15504C, had a carb issue, it was missing the plug orfice and had a clogged/bad fuel pump, got those fixed and the motor started, ran beautifully for about 15 minutes, then started to rev down and back up down and back up then died and that was it, can not get it started again, checked spark and it is good, checked fuel pump and it is pulling gas as expected. Carb has been cleaned and rebuilt. Compression is 105/110. We sprayed starting fluid in it and still nothing. I was thinking maybe something the Manifold but would love some advice on this one before going into it to far. Seems like it warmed up and then did not want to run after that, I will try to start it cold tomorrow and report back. But why would it die when warm?

 

[racerone]

How did the motor run for you last season ?-----Did you install a new water pump impeller ?------And how high was the water in your test bucket ?-----Was it 6" above the impeller ?

 

[KC9000]

So new motor project, trying to resurrect it. Not much information on the motor besides the guy before ran it out about 30 minutes and it died and that was it. He supposedly did a carb rebuild and other things on it, but when I got it, when pumping primer bulb gas was spilling from front of carb, checked carb and sure enough the orfice plug number 58, part 23 on the carb diagram was missing, did a carb rebuild on it and put the orfice in, the fuel filter was completely bad, so did a rebuild on that. The water was about 8 inches above cavitation plate, and was pumping water really good. It started on second pull and idled beautiful. It was pumping a lot of debris out of the exhaust with water of course. That cleared after a few minutes and motor was running great, did the rev down and back up thing a few times then died and we could not start her again. We checked spark and it looked good, pulled fuel pump line and as we were pulling the string fuel was squirting out of the line, and compression was decent enough.

 

[OptsyEagle]

If you checked spark and it was good and also sprayed starting fluid in it (I assume right into the cylinder holes) and got nothing then it is either bad compression or your spark plugs are no good or the timing of the spark has shifted. The only failure I can think of where spark on both cylinders would fail at the very same time (while still indicating good spark on a tester) would be if the flywheel key was sheered, moving your spark timing to a useless position.

By the way, be careful using too much starting fluid since it has no lubrication. A mixture of gas and oil for testing would be better or seafoam which also has lubrication in it.

 

[KC9000]

Good to know, thank you for that. We used a quick spray and that was it. I am going to get new plugs and test that. Only did the spark test by eye ball.

 

[racerone]

That motor has breaker points.---A sheared key might result in a " no spark " condition.

 

[KC9000]

Got spark for sure, I am growing a suspicion that the float got stuck in the up position blocking the fuel, I am gonna take it apart again and check.

 

[KC9000]

So pulled the flywheel just to check cause that's what I did to my 20 hp mariner recently, key is good and everything looks great in that area. So I went back through the work I did, I think I had a part in the fuel pump flipped. . Found some junk in the exhaust hole, got that out. Was able to start the thing in gear...weird. after that I decarbed it, and swapped to new plugs after that. Now it has not shut off, it does after time start to rev down, but I set the idle a little high to avoid it turning off, it starts back up in 2 to 3 pulls . I will post a video as soon as it uploads.

 

[KC9000]

 

[OptsyEagle]

Motor sounds good. The problem with the fuel pump scenario being your original problem, is why did it not attempt to start when you used starting fluid? The starting fluid is to rule out fuel problems if it still does not attempt to start. Perhaps the starting fluid did not make it all the way to the cylinders. What spark plugs are you using? For those motors (1974-1976) the NGK plugs work a lot longer then the Champions. I suggest NGK B6HS or B7HS since those motors are prone to spark plug fouling. Do not use that motor for trolling for long periods of time unless you enjoy rowing back to the dock or getting home on one cylinder.

As for the junk in your exhaust. If it was black rubber it is your upper motor mounts disintegrating. If the power head does not wobble around too much, when starting it, I would leave it. New motor mounts are not cheap.

Kind of weird the pull starter worked when it was in gear. I thought they had something to prevent that.

All in all, it sounds better then mine. I don't even have a functional idle adjust on the side. I just use the throttle to idle down. It will idle down better on the boat when it is pushing a load.

 

[oldboat1]

The black stuff could also be from a partially disintegrated water pump impeller -- should check surface temp on top of head (ir tester is a great tool) Over 150-160F is too hot. Change impeller, of course, if you haven't done that.

Motor sounds good. You might throttle it down as you are doing in the uTube (your adj. wheel seems to work a little, anyway). I would do that in coordination with adjusting the air/fuel mix at the carb, assuming you can do that with the '75 (I haven't checked yet). When throttled down to where it runs slowly, if haltingly, try to smooth it would with the air mix -- same process repeated for lowest idle the motor will do.

edit. Make that lowest idle the motor will do, and still go in and out of gears without stumbling or stalling (sign it's a bit too lean).

 

[oldboat1]

Yup. Idle needle on top of carb. The idle chamber under the silver plug must be clean. Assuming that, try leaning out the mix (clockwise) 1/8 turn until motor coughs or quits. then back out 1/4 turn for best running.

 

[KC9000]

Awesome, love iboats for this reason, I appreciate the advise. I did hit it with a ir thermometer and highest temp reading was 155, we will be doing an impeller and thermostat on it as soon as they get here. The powerhead does not wobble much at all. This poor motor was neglected and is back from the dead. It spit out about 2 or 3 hand fulls of stuff and then the rubber showed up. Not sure where it was stored but it was in seriously bad shape. The gearcase oil looked good, changed it anyway. I have adjusted the needle and found what seems to be the best spot, turn it any way and it does not run the same. I started in in gear by lifting the lockout and pulling the rope, only did that cause it refused to start the right way, but after that it started a dozen times without issue.. But impeller, and New thermostat with a gasket for the cover are on order. Thanks again for all the good advice, greatly appreciated.

 

[KC9000]

Oh and yes it had BH6S NGK in it and I went back to the same when replacing them.