I have a '69 F-100... rescued it from a farmer for $1K. Had the engine rebuilt, new dual exhaust, took care of the few rust issues and have a show room paint job on her. The engine still runs rough. There's only about 1200 miles on the "new" engine. I replaced the original gas tank & fuel pump/filter. I can't decide whether it's a carb problem or ignition. When it gets up to operating temp.... I get small back fires and a very rough run.. if I stop at a light, it idles rough and dies. Then it will not start again until the engine cools off. I have a reman motorcraft 2bbl carb (rebuilt with holley parts) that was installed when the engine was rebuilt. I have no idea if it's adjusted correctly. Any help/suggestions would be great.
Thanks!

 

Is it a "miss" or a real "backfire"? Is the backfire out of the carb or through the exhaust? A backfire is usually a timing issue because the fuel is getting lit off at the wrong time. A miss or sputter can either be ignition or fuel related.

First step: Get yourself a vacuum gauge and timing light and try to dial in the idle speed and timing. And if you're running points, ditch 'em and install a Pertronix module - So simple a caveman can do it.

If that is unsuccessful, check the float level.. and while you have the carb apart, check for dirt and also to see if the accelerator pump has a small pinhole... it could be draining the fuel bowl after it has been shut off and causing a flooded condition. Thus, only when the truck has been shut off for a long time will it start because the fuel (which drained down the intake manifold) has had enough time to evaporate.

 

It misses... You're right...not a backfire. It misses a continually. I'm still running points, etc. I'll look into converting. Thanks.