Hi,

I'm from Germany and drive a '65 C2, 327cui, all standard. No tuning.

Perhaps an expert has some advice for me.

Last week I was in the Dolomites in Italy.

In extreme heat, 30°C and above, as well as when driving slowly uphill for several minutes, e.g., behind a truck or when standing for a long time at a construction site, the engine stalls.

Attempts to start it are unsuccessful; after waiting half an hour, it can be restarted, even with the help of starting aid spray. I noticed that no more fuel is spraying out of the accelerator jets when I accelerate, which means the carburetor is empty.

My suspicion is that vapor bubbles are forming in the fuel line due to the extreme heat.

The radiator fan constantly blows hot air backwards, including through the fuel line.

In addition, gasoline in Europe contains at least 5% bioethanol, which has a lower boiling point.

The fuel line to the fuel pump has no return line.

Does anyone have any ideas?



Many thanks.



Regards.

Udo

 

Udo, To help you, we need to know what engine and carburetor you have.
Your lack of fuel from the accelerator pump could indicate vapor lock in the fuel line but I would approach the troubleshooting from the basics.
A visual check of the fuel line for pin holes allowing air to be sucked into the line. Check all rubber hoses for cracks. Perform a pressure test on the fuel pump pressure, should be 5 to 7 psi. Is the fuel line routed near the radiator hose or touching it? Is the heat riser on the exhaust pipe functioning properly or frozen closed?
If a Holley carburetor, check the filter to assure it is not plugged and is installed correctly.
If you have the cast iron manifold, have the exhaust preheat holes under the carburetor been plugged to reduce heating of the carburetor.
Is there an insulator under the carburetor? Are the float levels set properly.
I have probably missed something, but these are a start.
Ron
P.S. We have 10% ethanol in our fuel and it boils out of the carburetor on a hot day and floods the engine making it hard to start. I have to open the hood when I park the car to allow the engine to cool which minimizes the problem.

 

Thanks for the quick reply.
Sorry, I forgot to mention a few things. The C2 has side pipes, the carburetor is an AFB 1552, and the fuel pump was new last year. Fuel pressure is difficult to measure; all pipes are solid. When starting with the pipe unscrewed, the pump delivers about 0.5 L/min. The engine runs well at full throttle. I've already insulated the pipe from the pump to the carburetor.
The rubber hoses on the tank and fuel pump are new.
Where are the holes under the carburetor for heating? How could they be sealed? I only drive in the summer.
I checked the floats in October 2024, and they're correctly adjusted.
There's an insulating plate under the carburetor.

It first happened in 2024 at the Corvette meet in Prague. It was very hot, stood still for 5 minutes, then drove jerkily for 1 km, and it stopped. Return trip on a tow truck.
After that, I tested everything I could think of that could reduce the fuel flow. One cause was a fuel filter at the tank outlet. It was only letting a small amount through. It was a simple US product in a metal housing. It had paper honeycombs inside. I suspect these had swelled due to the biodegradable content of the fuel. The filter has been removed.

My first idea would be to insulate the fuel line coming from the tank with Armaflex, as far as I can reach it.

 

Sounds like you’re taking a good path.

a couple other thoughts involve insulating the Carb itself from heat.

You could try adding a 1/2” phenolic space under the carb. And maybe a heat reflector shield between intake and carb might help keep the carb itself from

Summit racing carb heat sheild

 

You must remove the intake manifold to access the heat crossover. Then you need the special FelPro intake gasket set that includes the block-off plates. Dennis

 

I have had 3 vehicles that had pin holes in the fuel line that would begin to run rough and then die. Had to wait 30 minutes to get it to restart on 2, but it sounds like you have already checked those items.
I would think heat soak and vapor lock will not occur when the fuel is moving thru the pump and lines, thus your problem with it stalling while driving and no restart makes me think maybe the coil is weak or if you have points, the condenser is bad, or the ground wire from the point plate to the distributor body is broken and making intermittent contact.
Just more guesses.
Ron
If you have the cast iron manifold, there are two 3/8" +/- (9.5 mm) holes on either side of the primary bores where exhaust gasses heat the carburetor base. Plugging them may reduce the heat at the carburetor a bit, but it is better to block off the passages at the head in my opinion.

 

Hi,
Thank you for the advice.
I'll take a look at the holes under the carburetor and seal them.
I'd almost rule out the possibility of an electrical problem. The first thing I do when the engine stalls is briefly depressing the throttle to see if any fuel is spraying out of the accelerator jets. In that case, no fuel ever comes out. So the carburetor is empty.
In my opinion, very little fuel flows in the fuel line from the tank to the pump when the car is idling, and therefore has more time to heat up and evaporate.
Regards
Udo

 

I am not familiar with the Carter AFB 1552, but the early Carter AFB carburetors had a leather cup on the accelerator pump. It worked well, but would get worn quickly. Have you tried a new accelerator pump? If the accelerator pump has a rubber cup, is it alcohol resistant? When the engine is cold, does the accelerator pump work well?
Also the gas cap on the C2s is vented to allow air into the tank. Perhaps the vent is clogged and restricting fuel to the pump. Have you tried leaving the gas cap loose when this happens?
The engine bay of a Corvette seems very small and traps the heat. Another thing to try is to leave the hood open a bit to allow the heat to escape to see it the problem is minimized.
Others have claimed an electric fuel pump will minimize the vapor lock, but I have no personal experience using one to resolve vapor lock. There are a few threads on the forum about using an electric pump, here is one.
https://www.corvetteforum.com/forums/c1-and-c2-corvettes/3087577-vapor-lock-so-whats-the-cure.html
https://www.corvetteforum.com/forums/search.php?do=showgcs&query=vapor%20lock #gsc.tab=0&gsc.q=vapor%20lock&gsc.page=1
A return line to the tank should work, but I don't have any experience there either.
Ron

 

[QUOTE=R66;
Is there an insulator under the carburetor? Are the float levels set properly.
I have probably missed something, but these are a start.
Ron
P.S. We have 10% ethanol in our fuel and it boils out of the carburetor on a hot day and floods the engine making it hard to start. I have to open the hood when I park the car to allow the engine to cool which minimizes the problem.[/QUOTE]

I had that problem with my 62. I added a 6mm insulator between the base of the carb and the intake manifold---easilly available form US Auto parts vendors. BUT, you will have to be careful of clearance bentween the top of the air cleaner and the hood---It took some creativity and a lot of trial and error before I foud a combination that worked for me.
I also make a practice of opening the hood and propong it up at least 12mm whenever I shut down-----even in parking lots.
Both have worked quite well.

Best
Eddie
'62

 

Thanks for the help.
I checked the fuel cap is vented.
The accelerator pump works perfectly when the engine is cold and at normal operating temperature.
A 9.5mm insulation plate and a standard gasket are installed.


The holes that heat the carburetor base with the exhaust gases are sealed by the insulation plate, right?

Regards
Udo

 

It sounds like you are getting vapor lock. Your fuel pump may be weak and not pulling enough fuel up .Or your fuel lines could be getting too hot while going slow. Maybe some insulation around them, or an electric fuel pump away from the heat.

 

There is a thin stainless steel gasket / plate that goes under the carburetor gaskets to prevent the exhaust gasses from eroding the aluminum carburetor. The original gaskets have a smiley face like the passage in the intake manifold. It is a must if the holes are not plugged, but not needed if they are.
What fuel pump do you have? The original style bolts together and they have a history of the pin for the lever walking out.

 

The fuel pump was replaced in March 2024, BM4657.



If the engine runs normally at full throttle, I think the pump should be OK.

 

Hi,
A quick update: I've installed insulation on the side pipes and insulated the fuel line as best I can.
I can't test it because the gearbox is broken.











Regards

Udo

 

You said the gear box/trans is broken. Can you tell us more? Dennis

 

Hi,
yes, I can. After a 3000km tour through the Italian Dolomites, the gearbox produced very strong vibrations in gears 1 to 3. The 4th gear ran normally. The cause was a broken ball bearing.

 

Oh, that's not very fun. But at least you know what it was.

 

WOW, I have never seen a bearing race fail like that before. Is the case damaged where the bearing fits in?
Ron

 

hi,
No, fortunately not.
The probable cause is the incorrect installation of the countershaft. It protruded 1.5mm from the housing, which meant that the surfaces of the clutch bell and gearbox were not mounted parallel.
I had bought the car like this years ago from US.


Regards

Udo

 

Sorry to see that Udo. I hope you get I fixed correctly. Dennis