Heres the deal - 67 fastback with a 289. 2V autolite, replaced about 6 years ago (car has gotten maybe 1000 miles in the interim). When taking it out to drive it starts right up and runs strong. Can accelerate well, driving on highway and side roads. Then, about 20-25 minutes into the drive, it quits. Engine can barely idle, much less move the car. Engine restarts, but can not increase RPM's. If I sit on the side of the road for 10 minutes it will start again and run no problems (at least for the 5 minutes it takes me to get it back into its garage the last 2 times it has happened). At first I thought it was the fuel pump or filter. Could it be the fuel tank vent, the pump, some sort of ignition tuning? Fuel tank is <1 year old and new.

Please help, now is the season for driving.

 

Next time it quits check to see if you can smell gas, and if you have spark. That will help narrow down your search. You might also see how hot your coil is. Unless it is bolted to the exhaust manifold it shouldn't be too hot to touch.

 

I just popped in to say that I like your SN

 

Doesn't smell like gas. Don't know how hot the coil is. Can I test the coil without driving around and waiting for this to happen?

 

If it doesn't smell like gas you may not need to test your coil. If an engine quits due to lack of spark you can smell raw gas.
When it dies if you don't smell fuel, you probably don't have any in the float bowl.

To test the coil you need to get the specs for your coil. If it's stock that easy, it's in the service manual. If it's aftermarket you'd need to find their specifications. Coil specs vary wildly even within the same mfg.

 

It sounds to me like you are suffering from vapor lock. Meaning, the fuel in the bowl gets so hot that it vapor locks, turning into vapor instead of raw gas. Do you have a spacer under your carburetor? The phenolic ones work best to keep the heat away from your carb.

 

Did ya try replacin the fuel pump? (sorry if ya did and I missed it in the post)

 

Not likely a fuel pump problem since it runs strong for 25-30 minutes. I still think the carb is heating up and turning the raw gas in the bowl to vapor. The coil can be tested, as per Scott's instructions, by taking the coil wire off the distributor, and hold it very near the exhaust manifold. Turn the engine over. If you get a very rapid spark, then the coil is good.

 

something is getting too hot, proably the carb like soaring said

 

O.k. I checked the coil and its fine, good spark. Is there any way to verify the vapor lock theory. I can't think of anything I could look for. Would the engine still run if its vapor lock? When this happens I can get the car to idle very roughly, but no power, no acceleration.