My 1979 F-250 4x4 regular cab long bed with a 408 (351m bored and a 400 crank) and a 4 speed has a problem that's either carb or timing i guess. It shouldn't be anything else. But due to the normal operating temperature being around 160 and the very poor fuel consumption and the way it drives i am leaning toward carb.

Here's what it does. Just yesterday I took it on a 150 mile one way trip. Some times the truck would run so good i swear it was a brand new fuel injected truck, and sometimes it would start to "pop" and hesitate at random. When I started to pull a hill (with the same amount of throttle) it would sometimes start to pop and hesitate and when I floored it sometimes it does the same thing. When it starts to "act up", I can floor it and it will still get to 90 pretty quick and do it without a power loss besides for the split seconds when it seems to cut out from the hessitation. It also seems to pop through the exhaust when it acts up, but I think it runs rich.

So, going 75 on the high way with the temp at 160 and the oil pressure at 55, it runs perfect for 20 miles then acts up for 2 miles and then is fine again. like i said, the truck really moves and there isn't really a power loss, just pops and hesitations. I have a ****ty (but fairly new) pro comp ignition and hate it however i don't have the money to replace it right now. So what do you guys think? Do i need different jets, different spring in the accel. pump, secondaries adjusted, or what? Its a Holley 750 cfm carb.

Thank you guys,
TheBlueMule

 

Look at your spark plug. They should be brown to grayish-tan color and slight electrode wear. White is too lean.

 

160 is too cold. I check the ignition carfully for any loose connections. I have had problems with Mallory unilites being intermittant. If you have vacuum advance make sure it operates freely.