VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 Vapor Lock Problems

Guys,

It seems that boiling/evapoaration of the gas we get nowadays is a big problem these days. Until about 3 years ago, I never had a problem with vapor locking on my restored '39 Master 85 sport sedan. Now, though, I can't really drive it in the hot Carolina weather for fear that it won't restart.

I have to wait about 30 to 40 minutes for everything to cool down before it will restart. I switched to alcohol free gas after the last vapor lock episode but I'm not sure how much that will help yet.

I'm thinking about putting an electric fuel pump in the gas line between the tank and the stock mechaniocal fuel pump.

Does anyone have any advice or suggestions for me?

Thanks.

Hard to restart when hot could be a number of different things, what makes you think it's vapor lock? I'm not saying it isn't vapor lock, just thinking about all the old cars I've had that were hard to start when hot. Weak starter, timing off,points not set correctly or worn out,weak battery,etc.


http://www.twoguysgarage.com/forum/showthread.php?t=8434

39 _Floyd, Definitely check on what wawuzit suggested. But when I had this problem, It was suggested here that I change my battery cable size. I originally had 12 volt cables on. But what I needed was "oo"or "0000" cable size. I put 00 on mine because that's as big a size that the farm supply store had. But if you can find the larger size, I'd go with that. Mine starts much better, cold or hot! Hope this help's,
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Joe's 37

Have you wrapped a towel around the carby and poured water onto it? If it is vapor lock that will usually solve the problem. If it doesn't, look elsewhere. Obviously it is heat related. My "48" had that cool down problem for a while. It meant that when we stopped for fuel we had to push it away from the pumps and go shopping for a while which can be expensive. It turned out to be a problem with an old coil. We put a brand new Bosch into it and end of problems. Cable size helps too.

My carburetor has a ceramic base insulator under it. I put it on to solve the same problem. The insulator did change the height of my air filter/carburetor so I had to file down the air filter top screw to keep it from denting the lid (which I did dent the hood). Chevs of the 40's sells insulators. As the rest of the responses indicate it could be other problems, but with 90 and up heat this summer it does cause more problems. Maybe we should consult our magnificent sites feature of "Advanced Search" of previous posts for how the problem was solved before global warming. Good search term is "carburetor," good forums to search are "1937-42" or "1946-48" Good Luck, Mike

Gene posted this response in 2006:

Vapor lock occurs in the fuel pump/fuel line.Years ago some cars had a shield over and behind the fuel pump to direct moving (cool) air over it to prevent vapor lock.
I have never had a vapor lock problem with my old Chevrolets.Have had them cut out for a second or two after they sat and idled when real hot or resartred after sitting a few minutes when hot.Once going and the gas "flowing" problem corrected its self.I doubt if vapor lock will be a problem if the fuel pump is good.You could always do as the old Dorf flat head V8 drivers did it hot weather.Carry a gallon jug of water to pour over the fuel pump/fuel line when they vapor locked.Was a big problem with those engines as fuel pump pump was on top and to the rear of the engine, this made it necessary to pull the gas UP to the pump.Either they vapor locked or just plain overheated...was not a hot weather engine.
I could face 100 degree weather while crossing the "great plains" and don't even give it a thought.Have done it a few times with the old cars and never had a problem.Won't mention the year the Middle West meet was held in Hutchinson, Kansas and it was 110 degrees every day.
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Chevgene


Checkout my post in 2008, it has lots of good answers. Gene also talks about vaporizing fuel here with suggestions. I didn't post what Gene said because we all need to put our big boy pants on and learn to use our super index of past posts:

I have a Carter W1 Carb in my 41 sedan. I'm having problems starting the car after running it (several miles) and letting it sit for about 15 minutes or so. I can smell gas so I think there is an internal problem with the carb (leaking fuel into the intake manifold?). I have checked the float and it is set according to specs (1/2" and 1"). I don't have a gauge to set the meter rod adjustment so I don't know if this is causing the problem (the rod not seating closed). Another problem could be the float valve but it seems ok (no wear). I am even wondering about the fuel pump being to high a pressure? The pump is not the original so could be something purchased from the 60's to 80's (I'm going to check the pressure). I am only getting about 10 miles per gallon but the compression on all cylinders is low (mid to upper 90's and it uses a quart of oil about every 500 miles. The engine runs real good with no valve area noise. Any suggestions are appreciated. Thanks Mike
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Mike 41/77 Chevys

Your problem is more percolation than vapor lock. Vapor lock is a sign of a weak fuel pump which doesn't sound like your problem. With the intake manifold in intimate contact with the exhaust manifold the heat transfer to the carb is huge. The fuel gets boiled out of the float bowl and into the intake runners. When you try to restart it's like starting a hot engine with the choke on. There's no way to completely "fix" the problem that I'm aware of. Just plan to stay where you're at for a while when you shut off a hot engine.

It might not be relevant but I have a small story here.
My father used to own a a 1942 Canadian C15 Chevrolet COE truck.That was just after WW2 in the island of Crete. He used it for trading all over the island.
In the summer months often with temperatures over the 90s he should drive up and down the mountains with many stops to deliver or collect merchandise.The 216 was getting overheated and refused to start .
He had a very simple solution for avoiding vapor lock.
He had some large tomato's with him if the 216 was too hot he should slice a tomato in 2 then push the one half on top of the fuel pump and the other half on the side of the carburetor and hold it in place with a rug... and that was that!! the engine should always start.
PS. Tomatos were wery cheap at these times.

Jianis

Clothes pins. i dont know WHY they work...and i barley understand how...but they do.

I know they work also. The dragstrip back in the 60s had wooden clothes pins laying around everywhere. We made COOL CANS out of coffee cans. (copper tubing coiled in a coffee can and packed with ice) The big block guys would advertise CHAMPION N4 spark plugs as "Get your ice cold N4s here" The cooler the gas flow the more power !!!

I used to put clothes pins on fuel lines of my '49 and '50 F**d products. They dissipated the heat. Without them, I would almost always have a vapor lock on real hot days. I never had one if the pins were in place. Beamer

Clothes pins never worked for me or my buddies. I always ended up having to buy a fuel pump to fix the problem when it raised it's ugly head.

Actually the clothes pins don't dissipate the heat but insulate that portion of fuel line where they are attached. That keeps some heat from the line and thereby helps prevent fuel vaporization. Covering the line with aluminum foil held on by clothes pins was even more effective. It reflected the radiant heat and also provided a small amount of insulation.

I have also used "muffler bandage" on the fuel line between pump and carb with good results, looks a bit untidy to horrible.
Tony

I think that Tiny might have hit it right on the head - I suspect that it's really probably percolation of the gas in the carb! I forgot to mention it in my original post but the mechanical fuel pump is brand new, the battery is strong, the cables are 00 size, and there is no problem turning the motor over - it just won't start when it's hot. A wet rag around the carb and waiting a few minutes usually does the trick.

I've been driving this car for 30 years and never had this problem until just few years ago so I think the new gas with ethanol has a lot to do with it. I've been using a marine fuel stabilizer that is supposed to counteract the alcohol. Still, I had the (no hot start) problem again recently so I'm switching to a gasoline only brand.

I'd still like to know - does anyone in VCCA have any experience with putting on an in-line electric fuel pump as a cure for the fuel percolation problem? If I do this, would I need to add a regulator in front of the carb to adjust down the fuel pressure coming in? Any suggestions would be welcome.

Thanks guys.

I don't believe an in-line electric pump would do anything to fix a percolation issue. The heat transferred to the carb will boil the fuel out no matter what type of fuel pump you have. The fumes will then settle in the intake runners resulting in a rich condition. A thicker spacer between the manifold and carb might help some as might a home made heat shield but I don't see how a fuel pump would help with a perc issue.

I remember hearing about vapor lock back in the '60s, but I've never experienced it with any of my cars. My auto shop teacher seemed to feel it was usually an overheating problem, and that is what we would go after. Usually a radiator/block flush would take care of it, but on occasion we would pop out the freeze plugs and scrape/chip rust in the water jackets, suck out the residue with a high power vacuum, and finish up with a magnet.

Moving fuel lines away from the head, block and manifolds was another thing, along with putting a spacer or two between the manifold and carb. Be sure and put gaskets between spacers, manifold and carb. The main thing here was "keep your gasoline away from the heat!".

I've also heard that it is cause by "residual heat buildup". I'm pretty sure that these cars didn't do this when new, so what is different? Most likely it concerns rust and corrosion in the block causing heat pockets that affect gasoline in the vicinity.

Anyway, that's my story and I'm sticking to it! They were not built to act up like that, so vapor lock is a symptom, and there has to be a cure. Excess heat would seem to be the main problem, so do whatever needs doing to get rid of the heat or get the fuel away from it.

And adding an electric pump to push even more gas into an already compromsed system doesn't sound like a good idea.

Yes highly volitile gasoline is a problem in hot weather!

I never ever had a vapor lock problem with a six cylinder Chevrolet from a 34 up thru a 62. We liked the Chevrolet straight six at home, because they would burn drip gas (casinhead) without any problems. A Flathead F0RD V/8 car or truck, with the fuel pump on top of the engine, would absolutely vapor lock any day with drip or regular when the outside air temp got close to 100 F. and in Wichita County, Texas that could be any day from the middle of March right up thru October. A vapor locking car won't just be hard to start when they are hot, but will shut down the engine driving down the highway on a hot day.

The percolateing carb problem causes hard starting mainly because the manifold is filled with gasoline vapor without any air, the engine is usually flooded, and the best way is to hold the accelerator peddle to the floor, DON"T PUMP it, and crank the engine for 15 or 20 seconds and then with the accelerator still on the floor, let the starter rest for 15 seconds, then crank again for 15 seconds, this will allow air to thin out the gasoline vapor and get air into the manifold and cylinders and have a air-fuel mixture that will fire. When the engine starts to slowly fire and rotate ease off the accelerator till it is running smoothly.
The engine isn't starving for gas but usually has too much gas and not enough air, because the gasoline in the carb vaporizes because of the heat and fills the manifold and cylinder. an electric fuel pump is not the answer. all the gasoline in the carb float bowl that vaporizes is quickly filled with the mechanical fuel pump while the starter is cranking the engine.
You also need to keep the aircleaner clean and be sure the choke is fully open anytime you are starting a hot engine. Of course this is not applicable if your fuel tank is empty or the fuel line and filter is plugged up, that is a horse of a different color!

Here's a link to The Carburetor Shop web site:

http://www.thecarburetorshop.com/Troubleshooting.htm#Fuelleak

In their troubleshooting section, read the part titled "Fuel Leak by Throttle Shaft(s)". This is probably the best explanation I have seen so far of what causes the hot re-start problem encountered by so many Chevrolet drivers. While it is an explanation of why gas leaks out of the carburetor at the throttle shaft, some of that gas that is dripping down onto the throttle plate leaks by the plate and collects in the intake manifold and results in the engine being flooded.

I proved this to be the case on my 40 1/2 ton pickup, which had typical the hot re-start problem. There was a glass bowl type fuel filter installed in the fuel line just before it entered the carburetor, and I installed a positive shutoff ball valve in the line just before the fuel filter. On a hot day, after the engine was fully warmed up, after shutting the engine off, I would close the ball valve. Then, after 15 or 20 minutes, when normally the engine would be flooded and take excessive cranking to re-start, it now started immediately. However, as soon as the engine started, I would lift the hood and open the ball valve. If I opened the valve too quickly, I could see a rush of gas vapor bubbles flowing through the fuel filter, and the engine would immediately die due to the excessive vapor entering the carburetor from the fuel line. The only way to keep the engine running was to slowly open the valve with one hand, while revving the engine using the throttle linkage with the other hand (and burning the fingers in the process). Even after the engine would stay running, you could still see vapor bubbles coming through, and the engine would run rough until relatively cool gas from the tank finally displaced all the vapor, then everything ran fine.

Obviously, this is inconvenient and was only a test to try to prove what was happening.

On my 37 pickup, without a shutoff valve in the fuel line, I tried a different approach. I plumbed in a bypass or re-circulating line, including a needle valve, around the fuel pump. On a hot day, I would open the needle valve a couple turns after starting the engine for the first time, then just leave the valve open. After a hot shutdown, the gas vapor pressure building up in the fuel pump and in the discharge line to the carburetor due to the heat in the fuel pump, instead of overwhelming the carburetor float valve, would simply flow through the needle valve and recirculating line back to the suction side of the pump, where it could then flow back to the tank. On re-start, the engine would start right up, though it would run rough for a few minutes, since the entire line from the pump inlet back to the tank was full of a mixture of liquid and vaporized gasoline. I think if the re-circulating line were plumbed as a separate line all the way back to the tank, the rough running after hot re-start would be eliminated. Another problem I noticed is that after sitting all night, if I did not close the needle valve before attempting to start the engine for the first time, the engine would not start--evidently there was too much fuel recirculating around the fuel pump through the needle valve and re-circulation line instead of going to the carburetor. But once the engine was started, I could leave the needle valve open and the engine would restart every time.

I conducted this experiment last fall, and before I was satisfied with the results, the weather turned cool and couldn't do any more testing under summer-like conditions.

FYI, my fuel line from the tank to the fuel pump was copper, which is not satisfactory, though it makes it easier to do plumbing experiments. My re-circulating line broke at one of the compression fittings, causing me to loose about a gallon of gas onto the pavement of a local restaurant parking lot. Don't use copper tubing for your gas line. And, always carry a fire extinguisher.

These experiments were not intended as fixes, but rather, to satisfy my curiosity as to what was causing my engine to flood after a hot shudown. I now know what the problem is. The real challenge is to come up with an elegant fix--that is, one that is simple, effective, and doesn't alter the stock appearance of the vehicle. I'm open for ideas.

Mark

I remember that my fathers 36' chevy used to vaper lock on him a few times. what he did was he found a automatic transmission cooler line. It was about six inches long and was "U" shape and had about a dozen fins on it. He installed it just before the carb to where the engine fan would blow on it. It did not look bad, but it was strange looking and it did work. I do not remember what kind of car the cooler line came off of. It did remind me of an old refrigerator coil that came from an old ammonia gas refrigerator, and it looked better than three or four clothes pins stuck on the gas line.

MrMack,
Your explanation of the problem is what I sometimes experience in my 216 engines and is what I remember concerning the old Frods. Most of the remembrance is taken from the days (1940s and early fifties) my father ran a garage and radiator shop down in Piney Green, NC and later in Jacksonville, NC (Camp Lejeune Marine base property was across the road (NC Highway 24) in both locations. (Sorry about this last bit of nostalgia. )

Anyway, about the only cars I recall that experiencing "vapor lock" were flathead V8 Frods. Consensus was that the problem existed mainly owing to the location of the fuel pump. It seemed that too much heat (as in over-heating) made the problem manifest itself with even more frequency and with greater intensity (longer period of time needed to wait for the vapor lock to recede. Just as you explained.

I think you pretty much "nailed" this one.

Well, enough about Frods. After all, this is a Chevrolet forum. Grin
Best,
Charlie

BTW for Mark: You sure went to a lot of work in trouble-shooting the problem with the 216. My hat is off to you for your diligence and clear explanation of what you did.