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Decided it was time to take the car on a short test drive about town yesterday. It was a hot (90 deg.) summer day in S. Calif. After about 3 miles I headed home and 1 block from home things came to a gasping halt. Got out and checked finding the car had gas in the tank, plenty of spark, but no gas coming out of the carburetor jets. Checked the pump and it was not pumping.

Let the car cool for about 30 minutes and it started right up. Hence the Dreaded Vapor Lock conclusion.

The fuel line runs down the frame from the tank to the engine compartment so it should be OK there. There is about 2 feet of tube inside the engine area before it gets to the pump and it is close to the frame.

The car has a '33 downdraft carb & manifold system. The question I have is there suppose to be a heat shield between the carb and the exhaust manifold. If so can someone out there send me a photo so I can make one that looks correct?

In the interim, I'm going to replace the regular gas with high octane gas that has a higher boiling point.

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Do you have the shield over the fuel pump?

Vapor Lock usually occurs on the vacuum side of pump (tank to pump), not pressure side (pump to carb), as liquids boil at lower temps when subject to lower pressure (aka vacuum).

My Stromberg EE-22 ('34 Eight) has a stamped steel heat shield around the part of the fuel bowl facing the exhaust manifold. It is apparently a component part of the Stromberg carburetor though not listed as such among the carburetor parts in the 33-36 Parts List for Eights and Super Eights. From your photo your carb is missing this.

These engines with the fuel pump on the opposite side of the engine from the manifolds are typically quite immune to vapor lock, perhaps the carb fuel bowl shield will solve your problem, I've never in 50+ years of driving this car experienced vapor lock.

PS. See page 80 of the 33-36 Parts List, "Carburetor Heat Deflector", p/n 210442.

Changing to a higher octane fuel is unlikely to reduce vapor lock. The boiling point of the fuel is unrelated to the octane rating. BP had an article on this topic some years ago, it was clear on that point.

My fuel bowl (glass) is on the inlet side of the fuel pump. During this episode of vapor lock the fuel bowl was always full of gas. I knocked on the side of the carburetor in case the float needle was stuck in the closed position

I believe the BP article was back when lead was added to prevent knocking. New grades do not have this anti-knock preventive in them.

Since gasoline is a made up of hundred of compounds, it does not a a boiling point as such. It has a point at which lower boiling compounds transition from liquid to vapor and begin to distill off. It is these compounds that cause knocking in carbureted engines that makes knocking. I think premium has less of the the more volatile components. It would be these volatile fractions in regular gas that would contribute to the formation of vapors.

Owen_Dyneto answers and solves your non-problem. He has never suffered vapor lock in half a century of Packarding for the simple reason that inline 6s and 8s w/ all their original bits do not vapor lock.

Those with inline engines insisting they've had vapor lock have other issues and/or wrong diagnosis. In 47 years of driving Packards on both coasts and across the continent in all kinds of weather, have never had an instance of vapor lock.

The only vintage/old/collector/special interest/"Classic" cars i know of which have are Cadillac, Cord, Ford V-8s in which the placement of the carburetor is begging for this malady.

Lovely engine, yours. And downdraft was of course a smart upgrade.

The placement of the fuel pump has a lot to do with a vehicles tendency to vapor lock. High mounted pumps or pumps located near exhaust manifolds will have a greater tendency to vapor lock. V8s are more likely to have carburetor boilover (flooding) issues, but it can afflict many vehicles in hot weather.

Dave,

Could you please post a picture or 2 of the heat deflector on your 34.

When I bought the car it was almost completely apart (engine, trans, and rear end excepted). Parts were scatter in 3 or 4 different building and unlabeled. and mixed together. It was a basically a 2 ton plus three dimensional puzzle on steroids'. There may have been a deflector that is still in Vista Calif in one of those buildings.

Gas with 10% ethanol can cause vapor lock, 15% is even worse. The vapor pressure of Ethanol is much
lower than the vapor pressure of Gasoline. The addition of Ethanol changes the
temperatures, at which various V/L ratios occur. Adding 10% of Ethanol to Gasoline – as is
currently done drastically reduces the V/L ratio temperature. Therefore a
critical vapor liquid ratio, which can cause vapor lock, will be reached at lower temperatures with Gasoline-Ethanol blends than with regular Gasoline.

Try making a phenolic spacer for a heat shield under the carburetor using the gasket as a template. Phenolic flat plate material in different sizes and thickness can be found on eBay.

I had success in stopping vapor lock in my 47 Custom by adding a small amount of Diesel. A five percent amount worked well with no odor or smoking from the Diesel.

The underwood temperature in that car was probably a primary cause. I would need to use a rag to lift the hood to prevent burning my hand. The engine coolant temperature was in the normal range and the engine never overheated. But the high under hood temperature was something I had not experienced in any other car.