Stalling when engine is hot and under load

[jblair630]

A few months ago bought a 1974 Super Beetle that is in pretty good shape for being 50 years old.  
So here's the particulars about the car:
1600 dual port engine type: AH
I have 2 carbs: the 34-Pict3 that came with the vehicle and a brand new Brosol H30/31 that my father sent me (its a long story)
Since getting the car I have replaced the fuel pump and all the rubber fuel lines.  The gas tank was out of the vehicle so I took the opportunity to clean and reseal the inside of the tank. 
I replaced the 009 distributor with an SVDA. New rotor and cap. New points and condenser. New coil. New spark plugs and wires. 
When I got the car running, the battery would not hold a charge so I replaced the regulator (Motorola alternator and regulator) and now charging system works fine.  The GEN light stays on when the engine is off and the key is in the OFF position, moving the key to the ACC position will turn the GEN light off and the OIL light will come on.  Starting the engine will result in GEN light staying off and the OIL light going off when oil pressure is acceptable.  I have tried tracking down the GEN light issue and have not been successful so far.  I have cleaned and tightened all electrical connections that I could get to including the body to transmission strap.  I tried taking out fuses but still no luck.  

The car ran well for a couple of months when I noticed a significant loss in power and a lot of noise.  Did some investigating and one of the rocker studs on the 3-4 side of the engine had sheared off. Replaced both of the studs on that side of the engine and checked the 1-2 side as well.  They seemed to be in good shape but I changed them just to be on the safe side.  Since that time valve clearances have held steady and the heads seem to be in good shape.

So here's the issue:
Car starts easily.
Idles well. Warms up from closed choke to fully open in three to four minutes. 
First five to ten minutes car drives perfectly. After that time the engine stumbles for a couple of seconds, then hesitates and dies. 
Trying to start the car immediately results in no start just cranking. Waiting for a moment results in car starting easily and idling well. Putting the car under load (shifting into first gear) results in engine dying again immediately. After restarting car, engine will idle well and sounds perfect. Putting the car in gear and creating the least bit of load will stall the engine. High revs and slowly releasing the clutch will get the car moving but if there is any significant drop in rpm then the car will stall immediately. After engine cools off (back to ambient temperature) it will start and run again as before. 

Here's what I've done:
My first thought was vacuum leak so I replaced the boots and the gaskets for intake manifold. No change.
I've tested everywhere I can think of for a vacuum leak from the body of the carb to the intake manifold connection on the head. No leaks.
I've checked the fuel pressure and the pump is putting out about 3.1 psi.  
I've ruled out the carb since the exact same thing happens whether I have the 34-Pict3 or the H30/31. I cleaned both carb bodies, jets, and adjustment screws.  Got a rebuild kit for the 34-Pict3 and replaces all the gaskets and the needle valve, etc.  I have adjusted both to spec in the Bentley. No change.
I have set the valves, point gap, timing, and idle several times with no change in the problem.
I've checked the coil and even switched out the new coil for the one that came with the car.  Testing the coil showed good strong spark in both.
Someone suggested testing the condenser since newer ones are often shoddy and prone to failure.  The suggested testing procedure was to look at the spark that jumps the point gap.  A weak spark was a sign of a good condenser and a strong, bright spark was a sign of a condenser about to fail.  This doesn't seem logical to me but I did the test anyway and there was a strong, bright spark that jumped the point gap.
I have questions about the alternator.  It seems to work just fine but I'm wondering if there is something inside that gets wonky when it gets hot and then resets when it cools down.  If there's any tests you can think of then I'll conduct them and send back the results.

The point of all this is that I have tried everything that I can think of to resolve this issue.  When the engine heats up then something expands to create this issue and when the engine cools down whatever it is returns to normal.  I'm at a loss and frustrated. The good thing is that my interest in finding out what is going on here is greater than my desire to do something to the car that I would certainly regret.

Thanks
Jeffrey

[Amskeptic]

A few months ago bought a 1974 Super Beetle that is in pretty good shape for being 50 years old.  
So here's the particulars about the car:
1600 dual port engine type: AH
I have 2 carbs: the 34-Pict3 that came with the vehicle and a brand new Brosol H30/31 that my father sent me (its a long story)
Since getting the car I have replaced the fuel pump and all the rubber fuel lines.  The gas tank was out of the vehicle so I took the opportunity to clean and reseal the inside of the tank. 
I replaced the 009 distributor with an SVDA. New rotor and cap. New points and condenser. New coil. New spark plugs and wires. 
When I got the car running, the battery would not hold a charge so I replaced the regulator (Motorola alternator and regulator) and now charging system works fine.  The GEN light stays on when the engine is off and the key is in the OFF position, moving the key to the ACC position will turn the GEN light off and the OIL light will come on.  Starting the engine will result in GEN light staying off and the OIL light going off when oil pressure is acceptable.  I have tried tracking down the GEN light issue and have not been successful so far.  I have cleaned and tightened all electrical connections that I could get to including the body to transmission strap.  I tried taking out fuses but still no luck.  

The car ran well for a couple of months when I noticed a significant loss in power and a lot of noise.  Did some investigating and one of the rocker studs on the 3-4 side of the engine had sheared off. Replaced both of the studs on that side of the engine and checked the 1-2 side as well.  They seemed to be in good shape but I changed them just to be on the safe side.  Since that time valve clearances have held steady and the heads seem to be in good shape.

So here's the issue:
Car starts easily.
Idles well. Warms up from closed choke to fully open in three to four minutes. 
First five to ten minutes car drives perfectly. After that time the engine stumbles for a couple of seconds, then hesitates and dies. 
Trying to start the car immediately results in no start just cranking. Waiting for a moment results in car starting easily and idling well. Putting the car under load (shifting into first gear) results in engine dying again immediately. After restarting car, engine will idle well and sounds perfect. Putting the car in gear and creating the least bit of load will stall the engine. High revs and slowly releasing the clutch will get the car moving but if there is any significant drop in rpm then the car will stall immediately. After engine cools off (back to ambient temperature) it will start and run again as before. 

Here's what I've done:
My first thought was vacuum leak so I replaced the boots and the gaskets for intake manifold. No change.
I've tested everywhere I can think of for a vacuum leak from the body of the carb to the intake manifold connection on the head. No leaks.
I've checked the fuel pressure and the pump is putting out about 3.1 psi.  
I've ruled out the carb since the exact same thing happens whether I have the 34-Pict3 or the H30/31. I cleaned both carb bodies, jets, and adjustment screws.  Got a rebuild kit for the 34-Pict3 and replaces all the gaskets and the needle valve, etc.  I have adjusted both to spec in the Bentley. No change.
I have set the valves, point gap, timing, and idle several times with no change in the problem.
I've checked the coil and even switched out the new coil for the one that came with the car.  Testing the coil showed good strong spark in both.
Someone suggested testing the condenser since newer ones are often shoddy and prone to failure.  The suggested testing procedure was to look at the spark that jumps the point gap.  A weak spark was a sign of a good condenser and a strong, bright spark was a sign of a condenser about to fail.  This doesn't seem logical to me but I did the test anyway and there was a strong, bright spark that jumped the point gap.
I have questions about the alternator.  It seems to work just fine but I'm wondering if there is something inside that gets wonky when it gets hot and then resets when it cools down.  If there's any tests you can think of then I'll conduct them and send back the results.

The point of all this is that I have tried everything that I can think of to resolve this issue.  When the engine heats up then something expands to create this issue and when the engine cools down whatever it is returns to normal.  I'm at a loss and frustrated. The good thing is that my interest in finding out what is going on here is greater than my desire to do something to the car that I would certainly regret.

Thanks
Jeffrey

Please make a note of coil temperature next time the car dies.
Colin

[jblair630]

Update:
Ran the car around the neighborhood until it stalled. Coil was warm but not hot. I could hold it in my hand comfortably. Metal part of the distributer was very hot. I could touch it but not for more than a second or two.
Some additional observations since I was being hyper-aware: When the engine stalled it definitely felt electrical, like someone had pulled a plug instead of a sputter like a fuel issue. Also when I restarted the car and pushed the clutch in the rpms would drop over the course of a few seconds and the engine would die. I did this four times in a row with the same result each time. After allowing the engine to idle for a couple of minutes I could push in the clutch with no drop in rpms. However trying to get first gear engaged led to the same results as mentioned before. Engine would immediately stall but revving the engine high and slowly engaging the clutch will get the car moving briefly.

Let me know if there's anything else I can check or test.

Thanks
Jeffrey

[Amskeptic]

Wasn't that fun, Jeffrey?

A build up of junk in the fuel line inside of the tunnel, cleared out by YOU.

We did take the long way around ... another update at your convenience, please.
Colin