First post on this forum, I really need some help. Please!
I have a 1966 with a 1968 302, the car starts and runs perfectly and idles great initially, has good power until I drive it for about 35-40 minutes, or roughly for 15 miles (dont ask why, but always at that point, that's my usual commute). In stop and go traffic it never even tries to backfire or stall, runs awesome, temperature is fine, its even running pretty cool since it has an electric fan. Then it suddenly starts idling roughly, popping, and backfiring horribly under acceleration. Until after about 3 minutes it just dies and is nearly impossible to start up again.
Changed spark plugs, distributor cap looks intact, points look fine, and timing seems ok since it runs perfectly before it goes haywire.
Seems to be something happening when it heat ups, but it is nowhere near overheating, what could this be?
Thanks

 

It almost sounds like a wire has a bad connection and when the wire warms up the connection gets worse. Maybe check the voltage to the coil and then again after it starts acting up.

By the way, I would ditch the points and get a Pertronix Ignitor to replace them.

 

I have been wanting to do this for a while, which one would you recommend? Ignitor I or II? I have read multiple opinions on these. Thx

 

It may be the fuel filter, I had a 77 that did the exact same thing. It would run fine for about 30 minutes until the filter plugged itself off with rust particles, after sitting a while the rust would settle and fall back from the filter membrane and would run fine for another 30 minutes or so.

 

I agree, sounds more like a fuel issue than anything else. Replace the fuel filter(s) and check the carb fuel bowl(s) for rust/dirt particles.

As far as the Pertronix goes, I'd recommend the Ignitor II. It has an automatic coil shutoff to keep from burning out the coil if you leave the key on with the engine off, and it also offers variable dwell. The downside is that you need to bypass the stock ignition resistor wire under the dash to run the Ignitor II. The original Ignitor unit will run off the factory ~8V.

 

It does sound like a it could be fuel related too. The filters are cheap so, try that.

I had a similar issue on mine when it as a 200 and the coil wasn't getting enough voltage, because the end of the wire was buggered up.

 

I was talking about this. It allows you to retain your factory distributor. I didn't think it was available in II form.

http://www.pertronix.com/prod/ig/ignitor/default.aspx

But sure enough, here it is.

http://www.pertronix.com/prod/ig/ignitor2/default.aspx

I know alot of people that have used the I and like it.

I have a Pertronix Billet distributor with flamethrower II coil and it works well. Im happy with it. I had to bypass the pink resistor wire so the coil gets full voltage on not the factory 8V.

 

Thanks for all the responses, I havent had a lot of time this week to check most of these things, but I will this weekend.
As far as any "bad fuel" problems, would this be affected AT ALL by the engine being run for a long time? I say this because the problems start AFTER running the engine for about 35-40 minutes...before that she runs really strong and idles perfectly.
I was also looking into a coil problem which is what made sense, and then I noticed that somehow the cable going into the coil was resting on the block and was beginning to melt. I looked over it and apparently it did not go through the actual cable jacket, but it did melt the black wire cover. Could this be what was causing this? Or is the actual coil going bad? I intend to replace this wire regardless, but I dont really want to start changing unneccesary parts.
I also intend to upgrade to the Pertronix kit, but would like to see if that was the problem to begin with before i do anything.

 

U could pull the line befor the filter let it run into a clean container and check for contanimates. but melted wire could be a sign. if your tank isnt new it may b benifical to check it out

 

Well just a small update, this weekend I replaced the wire to the coil and placed it far away from heat and the problem appears to be resolved. I drove the car for about an hour, and she is running great.
I am still planning on going to the pertronix unit and changing fuel filter, and testing her on longer runs, but she is good now, thanks for all your input!!