NEED HELP - 1970 440 BOGS & DIES OUT AFTER 20 MINUTES to HALF HOUR DRIVING

[PGio]

WHAT CAN CAUSE THIS? Please read all of this before offering advice. Thanks!
Here's the issue:
70 Challenger R/T. Stock 440, Auto Trans. Original Distributor with that retarded emissions retard module on it. Car runs nice on start up and first 15 minutes. After that it bogs when you give it gas, almost dies out, idles but will not accelerate. Have to pull over, let the car cool for 15 minutes, then drive. Same thing happens again. Happening for a year now since I got the car.
Carburetor was checked and rechecked by a pro - it is fine.
Here is what has just been done....
New points and condenser. Tune up. New plugs (wires are fine). A different 1970 distributor vacuum advance and module were installed. Oil filter change. Timing set and checked.
WHAT CAN CAUSE THE CAR TO BOG AND NOT ACCELERATE AFTER 15 MINUTES??
IT IS ALREADY AT FULL OPERATING TEMPERATURE AND RUNNING FINE.
WHAT CAN HAPPEN TO CAUSE THIS?
Can't be fuel filter clogged, it would run lousy all the time.
Can't be plug wires, it would run lousy all the time.
Can't be carb settings, it would run lousy all the time.
Can it be ballast?
Can it be Voltage regulator?
Can it be...????

 

[mrmopar340]

Vapor lock maybe? Have you tried a spacer under the carb or a fuel line cooler from the pump up.

 

[Xcudame]

Is the choke working properly and opening up after warm up? Which carb are you running? Electric choke? Manual choke? Stock choke heated by intake? I'd make sure the choke is working properly. Are you running stock exhaust with the temperature controlled valve on the passenger side? Is it working properly?

 

[mopar jack]

what about the coil?

 

[Chryco Psycho]

Are you using a mechanical fuel pump , the pushrod is probably worn down & too short to fully cycle the pump

 

[pschlosser]

I'm with @Xcudame and my first instinct is it's caused by something involving the carburetor.

Can't be carb settings, it would run lousy all the time.

You're probably right, but the choke IS supposed to be changing things as the engine heats up. Another carburetor circuit (Hot Idle Compensator) activates only when the engine (and/or carburetor) is hot.

Most of my post presumes the OP is using the correct factory OEM Carter AVS Carburetor. And also the car engine is not overheating during the break-down trouble they are seeing. It sounds like the engine is getting too rich when hot.

I recommend you check the choke and confirm it is wide open when engine hot and even after the engine cools after those 15 minutes, you mentioned when broken down. I think it should still be wide open.

After that, vapor lock is sounding stronger. Confirm there isn't an obvious exhaust leak blasting onto your fuel line, or something else that may be heating the fuel, such as a fuel line laying on the intake manifold near the choke.

Even with a failing fuel pump that only seems to fail when hot, I think you would still be able to accelerate moderately, if the engine indeed idles when this problem occurs.

If you don't have one already, try the "correct" 1/4 thick flange gasket to help minimize engine heat heating the carburetor body.

Oh yea, if it's an automatic car, the Carter AVS Hot Idle Compensator should also be working to minimize a too-rich condition when engine hot(-rodding). I have seen hot-rodders plug/disable these, over the years. If this circuit has been disabled on your carburetor, that may be the source of your troubles.

 

[Challenger RTA]

When I was driving some company vehicle that were mostly fords. A common practice in the 70's and 80's when it would vapor lock. The practice was to take off the gas cap and put it back on. Then you were on your way this happened a lot. Give it a try when it happens it might help narrow it down.

 

[Bret Schneider]

Banana in your tailpipe?
I realize this would be uncommon on a performance car but you mentioned the car was stock so I'll throw this out there. What you're describing are the classic symptoms of an engine with an exhaust restriction. Usually a problem with the cat converter in "todays" cars. Any chance of a muffler internally collapsing?

 

[michiganhotrod1]

Stock iron exhaust manifolds? Is the hat control valve stuck closed? This will direct hot exhaust under the carb with resilting vapor lock.
Mark

 

[PGio]

Hi All - the replies are greatly appreciated. Addressing them in order.....
1) Regarding vapor lock that a few of you mentioned... I thought about that and drove the car with the gas cap loose, it still happens after 15-20 minutes.
2) Stock choke heated by intake is working perfectly. Checked that several times. Car starts right up, idles well, then fully opens properly.
3) Coil- I don't know, thought about that too. Could the coil just keep heating even though under hood temp stays the same? And then the coil just craps out?
4) Fuel pump is stock mechanical. If the pushrod was too worn as suggested, the problem would be happening all the time wouldn't it? Not just after 20 minutes of driving.
5) Carb "Hot Idle Compensator" - Interesting! I didn't know about that circuit. Interesting, wonder if it is involved?
6) Stock exhaust, I believe the heat riser valve is functioning correctly. I will check as you said about fuel lines being too close to exhaust or any manifolds, and exhaust leaks hitting the lines.
7) If there was an exhaust restriction, I believe that would happen right from the get-go. Not after 20 minutes of driving.

I will check on what everyone here has suggested.
I am going to replace the stock "Cannister" fuel filter/vapor separator. Perhaps there is an issue there?
I am also going to replace the stock voltage regulator - the backing of it has melted down the firewall. But I do not think that could be the culprit. Does anyone here?
Can the alternator be heating up and not giving out enough? I do not think that would cause this particular issue.

 

[pschlosser]

I am going to replace the stock "Cannister" fuel filter/vapor separator. Perhaps there is an issue there?

This still seems like a fuel delivery issue. And I forgot all about that 440/426-only fuel separator canister! Yes, the vapor separator is on the list of things to check, and could be the cause of your problem.

The vapor separator canister can get clogged. But it's easy to unclog. Unless you want a new one, you can likely make the old one work. Clean it with a solvent, blow it dry, and test it. All openings should blow clear. The return tube has a 1/16-inch (0.060) orifice easily unplugged using a 1/16 drill bit.

 

[Bret Schneider]

"7) If there was an exhaust restriction, I believe that would happen right from the get-go. Not after 20 minutes of driving."

Like I said it's a long shot but worth checking. No, it doesn't work like the banana in the tailpipe movie example. That was Hollywood. Usually takes some time since the problem will be a restriction, not a total blockage from the start. I wouldn't be so quick in discounting it.

Putting a fuel pressure gauge on the car while driving and monitoring fuel pressure would be helpful. That would rule out a lot of potential problems. Not always so easy to do so what you might do instead is when the car stalls, pop the air cleaner and look down the carb while pumping the throttle and see if any fuel is squirting from the nozzles. Quick way of telling whether the carb is running dry.

 

[Challenger RTA]

I am also going to replace the stock voltage regulator - the backing of it has melted down the firewall. But I do not think that could be the culprit. Does anyone here?

This could be the problem. Given that amount of time. If the coil is not getting the correct voltage high or low it will over heat. All electrical devices haves a tolerance for a reason. The parameters are about 10% + or -. Electronics are more sensitive. And most of the time electronic work or they don't.
Way back when, when a voltage regulator was going bad. When changing gears there would be a back fire. Been there done that.

 

[larry4406]

This still seems like a fuel delivery issue. And I forgot all about that 440/426-only fuel separator canister! Yes, the vapor separator is on the list of things to check, and could be the cause of your problem.

The vapor separator canister can get clogged. But it's easy to unclog. Unless you want a new one, you can likely make the old one work. Clean it with a solvent, blow it dry, and test it. All openings should blow clear. The return tube has a 1/16-inch (0.060) orifice easily unplugged using a 1/16 drill bit.

I recall there being some threads about these. I am thinking other Mopar forums as I am somewhat new to this one.

Wrong size orifice installed on the reproductions. I recall seeing pictures somewhere of originals and repro's cut open showing the wrong orifice installations which lead to problems.

 

[Deathproofcuda]

Don't just tell us that the timing was set and checked, tell us where it is set.