71 60HP Johnson dies after 10 min running

[jksnyder]

This engine starts and runs well for about 10 min, then begins to gag and slows to idle speed. It sometimes quits and will not restart unless left alone for 3 or 4 hours then runs great again for 10 minutes. I've replaced the distributor, coil, power pack and confirmed proper fuel pump operation. No water in the gas and water pump working well. One suggestion was to have the carbs cleaned.....how could that be the problem if it runs well for 10 minutes??

 

[91cajun]

Re: 71 60HP Johnson dies after 10 min running

Just a guess but, does your fuel tank have a vent on it and is it open? I had a '67 5 HP Seahorse that would do similar things if I forgot to open the vent on the tank. Since you said you can leave it alone for a couple of hours and then it's fine again could be the vent or some sort of obstruction in the tank.

Then again could be a thermal problem. There are several experts on this forum that will probably know the answer.

 

[rickdb1boat]

Re: 71 60HP Johnson dies after 10 min running

The question I would ask is are you getting spark on all 3 when this happens? Check it out and see. That would rule out electrical. But I believe something electrical is getting hot after that 10 minutes and failing. It then cools and is Ok again until it heats back up...

 

[jksnyder]

Re: 71 60HP Johnson dies after 10 min running

Rick, thanks for your thoughts. When it fails it does sound like it's only running on two cylinders or even one at times and advancing the throttle has no effect at all.
I'm hardpressed to understand how heat can affect the electrical system....where would the most likely place be?
Jay

 

[jksnyder]

Re: 71 60HP Johnson dies after 10 min running

Thanks. I have a front mounted tank which has a built in vent thru the boat deck and have checked it for being clear. I've also connected the engine to a backup 5 gal.
portable tank in the rear and get the same results. I use two separate fuel lines with separate primer bulbs in my quest to eliminate those items as perhaps causing the problem. Jay

 

[rickdb1boat]

Re: 71 60HP Johnson dies after 10 min running

Coils would be my first thought. Powerpack next. Since you have replaced these already, it seems a long shot that any of these are the problem. But first you need to see if lack of spark is indeed a problem. Check the spark and let us know if you are losing a cylinder or 2...A Timing light works well for this...When it happens, hook the timing light up to each plug wire and if they are dead, no flash...Of course, that's if it will run at all after it bogs down. If not, get a spark tester at your local auto parts store and check it while cranking...

 

[dsinger]

Re: 71 60HP Johnson dies after 10 min running

Get a hair drier and heat your pack while it is on muffs. Just a bet but it is a hot pack.

 

[jksnyder]

Re: 71 60HP Johnson dies after 10 min running

To all of you that responded....my sincere thanks!

Found the problem to be one set of points. Heat from the engine caused the gap to change just enough to fail and then the engine would go to a rough idle or quit.

As is well now and I'm a happy boater. Thanks again!