72 Johnson Cutting Out

[mandvwagner]

This is a 100HP Johnson. It idles and runs great but the last couple of times we have had it out when going full throttle across the lake it will just die. It starts right back up. Any ideas on what would be causing this? I am thinking maybe its fuel related but not sure.

 

[flyingscott]

Try pumping the ball and see if that keeps it running.

 

[racerone]

Test run with a " known to be good " hose and portable tank.

 

[mandvwagner]

I will try that. I am thinking it's losing fuel pressure

 

[F_R]

Does it die instantly, like you switched the key off? When is the last time you pulled the flywheel and serviced the ignition system? Also, check all electrical connections, especially at the amplifier. Gotta tell you though, that was a problem even when new. Often the amplifier, but don't just assume. Make darn sure everything else is 100%. Did I say pull the flywheel and service the ignition system? Um....pull.....You get the idea.

 

[emdsapmgr]

When it dies suddenly, check for spark on all 4 cyls. Could be an ignition problem. My 72 100 hp would quit running and then not start till the engine cooled off. Found the timing sensor (385008) would heat up to normal temp and then would just quit. No spark at all. Once cooled down, it would run for about 20 minutes then shut off. This is not what yours is doing, but shows how flaky ignition problems can be.

 

[mandvwagner]

Ok so here is what it did Sunday. We went to the lake and ran around for about 20 minutes then anchored for a snack and let the kids swim (so we sat for approx 30-45 min). Fired it back up to take a couple laps before heading in. Half way thru the second lap around the lake it died. Hit the key nothing happened, starter wouldn't even kick. Got towed back to the ramp thanks to another friendly boater. Tried to start it again after I got the trailer in the water and nothing. Pulled the boat out of the water and tried again for kicks and it turned over. So could the timing sensor be it? I would still think the starter would turn over and try to start?

 

[emdsapmgr]

You could have a real overheat problem going on. It's possible the engine is severely overheating and you may not have a functioning hot horn. If the engine runs while it's overheating, the pistons will swell inside the cyl liners. When the pistons swell (get hot enough,) they will lock up inside the cylinders. If you try to restart, the starter will be bound up, since it can't spin the crank/pistons. Let it cool off for a few minutes and it may restart. Repeated lockups like this may be, will surely result in a severely damaged powerhead, so some investigation on your part is warranted. Borrow a laser temp gun and check the powerhead temps next time this thing locks up. Anything over 200 is really hot. Happened to me once and the 200 block cracked-scrap.

 

[mandvwagner]

The starters not even acting like it's getting power, there is no attempt that it was trying. But I was wondering about overheating.

 

[mandvwagner]

Well I got her started, one of the negative wires on the battery is loose. Haven't taken it out to see if the dying issue is gone but water flow looks good.

 

[F_R]

Oh-oh, loose battery cable. Great way to destroy the ignition system and alternator rectifier. Since it still runs, let's hope the ignition system is still OK. But if the alternator rectifier is blown (likely), the battery voltage will go low, and if low enough the ignition system will quit working.

 

[mandvwagner]

Yes I know they are sensitive, I shorted out the original ignition control trying to jump start it.