Hmm, where to start? I've got and '85 f150 with a 351w HO (115K). When the temperature outside is above 65 degrees (or somewhere in there) it doesn't start worth a darn. I pump the gas one, two, or even three times and it will not stay running after cranking. Sometimes pumping the gas 5 time it will start and stumble and then run rough but not die. I usually have to baby the gas to keep it running and after about 10 or 15 seconds then it will stay running on it's own. I had the carburator rebuilt back last Oct. and it started like a champ all last winter until it got warm outside.

After I go through this playing with the gas and it runs for a while, it will crack right off until the motor has cooled down, then I have to mess with it again. It doesn't miss at all when going down the road, but idles so darned rough at stop lights. I had the carb readjusted and new gaskets were put in between it and the intake manifold a month ago and the mechanic said that there was nothing more he could do about it, that that's the way it was. He said my compression was a tad low (they all ranged from 115 to 125 psi).

I had the timing chain changed along with a tune up(new plugs and wires) last Oct. also. I don't feel it's anything electrical because it runs so darned good on the road and never misses under load.

Any ideas would be appreciated.

 

I had a similar problem with my '83 F100 302. Then earlier this week, I did the obvious before doing any serious re-builds of the carb. I changed the plugs (they were old but clean), air filter (old one was really blocked up) and gas filter. Now in temps above 60F, it starts and runs first crack of the key.