'70 Beetle stalls when it warms up

[mateomorales]

Hi there folks. I am not a beetle enthusiast, but I have a little bit of mechanical knowledge (enough to get myself in trouble). My '70 beetle suddenly stalls when it gets up to temperature. It won't start it until it cools back down. I thought it might be the carb, so I rebuilt it (I'm at 7,000 feet and the timing is at tdc). But it still does the same thing.

I've got electronic ignition kit. The kit is 15 years old. I am not sure if it could be the culprit, but I figured it either works or it doesn't. Any ideas what the culprit could be?

[viiking]

There is a known issue with the bakelite pedestal piece that locates the fuel pump pushrod.

When the engine gets hot (usually too hot) the bakelite expands and jams the pushrod causing no fuel to the carburettor. Once it cools down and un-jams the pushrod, starting again allows the fuel pump to pump fuel again.

The fix is to sand the OUTSIDE of the bakelite piece so that it is much looser in the bore of the fuel pump section into the block.

What you need to do when the engine won't start is to pull off the top of carby and see if there is any fuel in the float bowl. If there isn't then the above problem MAY be what you are suffering.
_________________
1968 1500 RHD Lotus White Beetle since birth. In the hospital for major surgery
1966 Lancia Flavia Pininfarina Coupe - in the waiting room
Discharged: 1983 Vanagon, 1974 1800 Microbus,1968 Low Light,1968 Type 3

[Starbucket]

Is this when the car is just sitting in the driveway warming up? If so the heat riser under the carb. might be plugged you can test by feeling the heat riser under the manifold under the carb. after running for a min. or two, it should be getting too hot to touch, if ice cold it's clogged, remove and clean out.

[ashman40]

When you say, "... suddenly stalls when it gets up to temperature" do you mean it stalls as soon as the choke is fully warmed up and it opens the butterfly at the top of the carb? Or does it runs for a bit after the choke opens the butterfly?

One of the functions of the choke is to richen the air-fuel mixture while the engine is warming up. This rich mixture can hide a vacuum leak (lean condition), but as soon as the choke turns OFF the mixture goes lean and the engine can no longer run on its own.

A simple check for this is to cover the top of the carb (50%) with your flat hand while the choke is OFF (warmed up). This restricts the air flow down the carb. Slowly cover more and move of the opening with your flat sealed hand. At some point you will start to choke off the air flow and the engine should start the run slower (lower rpms). This is the same as closing off the idle to reduce the idle rpms. But if the engine rpms increase and it runs smoother... it indicates the mixture was lean and cutting off the air flow richens the mixture and the engine idles better. This is a sign there is an air leak allowing the mixture to run lean. Now you need to find the leak.
Spray carb cleaner at all the junctions and hoses. Any where that air could enter into the intake below the carb is a possible leak point. This includes the gaskets and seals between the carb, the intake and the heads. Spray these spots with carb cleaner while you have the engine running at a raised rpm (just enough to idle while you check). Spray all the hoses and their ends. If you spray a leak it will momentarily suck in the carb cleaner and the rpms will change (up or down). This means you hit a leak.
One common leak spot for decades old carbs is the throttle shaft openings in the carb body. Put the red straw on the carb cleaner can and focus where the throttle shaft exits the carb body. If it leaks here you need to have the carb professionally rebuilt where they can rebushing the opening in the carb.
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AshMan40
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'67 Beetle #1 {project car that never made it to the road }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!}

[johnnyvw164]

Sounds like electronics to me. Do you have a standard points etc you can install?

[mateomorales]

Thanks viiking-I did replace the fuel pump and bakelite pedestal. So I will check that there is fuel in the reservoir. But the fuel pressure maintains between 4 and 5 psi.

[mateomorales]

Starbucket-
Thanks for the suggestion on the heat riser. I will definitely check this out. Sounds like an easy test. It's a valid concern since I don't drive the car in the winter and I probably should have used fuel stabilizer or ethanol free fuel.

Ashman 40-
This is also a helpful and simple suggestion. I was so frustrated with this situation, that I bought another carby just to ensure that my old carb didn't have leaks in the throttle body (as you mentioned in your post). But the engine still had the same issues even with the new carby. I hooked the engine up to an RPM meter and it fluctuates between 500 and 800 rpm. I think the vacuum leak is definitely a possiblity. Unfortunately, if I find the leak, I don't think I have time (nor tools) to take apart a head, but this seems like a great place to start especially given the fact that rpms are bouncing.

I really appreciate all the input. It's really helpful for a guy like me who doesn't have all the necessary know-how (nor talent) to chase these things down. I'll be sure to report back and let you know what I find.

[mateomorales]

[mateomorales]

[mateomorales]

[mateomorales]

Thanks to all of you for your help on this. It turns out that the heat riser was indeed clogged like a chimney. I pulled the engine and it took some time, but I am sure it will be worth it.