Starts cold - does not run/or start when warm

[jerjag]

I have a 1971 Johnson 100 V4 (100ESL71C). Engine will start cold just fine, but after warming up (3-4 minutes) the idle will start to miss and engine will eventually stop running. Starting again is very difficult. At one time during it's idle the engine speed would increase and decrease before dying. I changed the fuel pump with no difference in performance. <br /><br />Thank you in advance for any suggestions.

 

[Solittle]

Re: Starts cold - does not run/or start when warm

Is the overheat horn going off? Also it may not be working so take the cover off the motor and start it. You should be able to put your fingers on the upper part of the head or block for a few seconds. If it is getting hot do the old replace the water pump & t-stats trick.

 

[Walker]

Re: Starts cold - does not run/or start when warm

At one time during it's idle the engine speed would increase and decrease before dying.

sounds like its running out of fuel. Check for tank vent, air leaks in fuel system, and give your carbs a good cleaning, probably need carb kits

 

[jerjag]

Re: Starts cold - does not run/or start when warm

No overheat horn going off. I also think it is fuel related; thank you for both your responses! Any tricks to overhaul the carbs or is it pretty standard?

 

[jerjag]

Re: Starts cold - does not run/or start when warm

One thing I forgot to mention - in checking the spark plugs there is a lot of oil showing. The mixture is 50:1. There was about 1/3 of a tank of old fuel (about a year old) which I added 2/3 of new (89 octane). I did not take the boat out last year. Could I have an 'stale fuel' problem?

 

[Walker]

Re: Starts cold - does not run/or start when warm

Stale fuel, certainly. Get rid of all that old gas and start with fresh. Stale fuel in the tank is another good reason to overhaul and clean the carbs. The carbs are pretty easy. Just take your time and pay attention to haw they break down. Clean each and every orifice sparkling clean.

 

[jerjag]

Re: Starts cold - does not run/or start when warm

Thanks for the good advice Walker - This is the first forum I've experienced that people do try and help people with problems. I'll do the carbs this weekend and see what happens.<br />Thanks again!!