Fuel Draining Back? NO!

Engine, fuel system, cooling system, heating, carburetors, exhaust, transmission, wheels, and other items related to the moving the car.

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Mike-Casella
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Fuel Draining Back? NO!

Post by Mike-Casella »

I keep seeing people posting close to the same question over and over again pertaining to the fuel draining out of their carburetor. I also see some people responding with that as a possible reason for a hard starting problem due to no fuel in the carburetor.

I have consulted with quite a number of carburetor rebuilders that have been in that business for many many years about this problem people keep having with the alleged fuel drain-back. They all agreed that on a Lincoln with a Carter AFB carburetor, it is positively impossible for the fuel to drain back. The fuel inlet is located above the level of the fuel that is in the float bowl, and the fuel will not jump up to it to run back down the line. The second fact that rules against that happening is the fact that the fuel pump valves are made to flow fuel in one direction only due to the fact that they are designed with spring tension holding the valve shut when it's not in use. In short, it is physically impossible for the fuel to drain out of a carburetor.

They also unanimously agreed that today's fuel is adding to this problem, with it's lower boiling point. If these cars had a completely new fuel system including all steel and neoprene lines, new clamps etc. they should not have any troubles. The Lincoln has one more thing going against it in it's fuel system design with the fuel pump located where it is. Any heat that is generated by the engine, naturally rises when the engine is shut down, resulting in the fuel pump and carburetor acting like a heat sink and in turn helping the fuel evaporate that much quicker.

Try not to compare how quickly a late model electronic fuel injected engine starts with it's fancy high pressure electric fuel pump, to a vehicle with a mechancal fuel pump driven off of a camshaft lobe.

Short of insulating all of the fuel lines, and using some kind of aluminum spacer under the carburetor to keep the heat away from it, I don't know of any miracle cure for this happening.

Mike
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Re: Fuel Draining Back? NO!

Post by autostick »

Thanks Mike for the facts on fuel; I always find your posts informative and well thought out. This is quite apropos considering the hot summer weather. I currently have the original Lincoln style fuel line insulation, meaning a foam rubber tube around the lines leading to and from the pump. Do you think this is adequate or should I put on better insulation such as cable-tied foil wrapped individually insulated fuel lines?
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Re: Fuel Draining Back? NO!

Post by Mike-Casella »

If the car is running fine, then what you have should be enough. Although it wouldn't hurt to have a little more. The fuel isn't going to get better, and with these cars that tend to thrive on fuel perculation probems, heavy insulation may just be what they need.
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TonyC
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Re: Fuel Draining Back? NO!

Post by TonyC »

For me, the hardest time to start is when the engine is cold, not hot. That is usually the result of a fuel component that is either out of adjustment or in need of rebuilding.

The nice thing about the Carter systems is that they can go a much longer time than normal--in fact, mine has outlasted any other system. They're durable, and they're designed to compensate to the best extent possible the harshness of vapor lock. The pump alone has an extra port that bleeds off vapor, and a heat shield is attached to the pump already. The only issue I had was when I had to rebuild the pump, but that was three years ago; the fact that it lasted 39 years says a lot. It's also good the pump can be rebuilt instead of having to throw it away and get another.

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Re: Fuel Draining Back? NO!

Post by 7579lincoln »

On my 75 Towncar, I am convinced it is not a fuel drain back problem and likewise, it is not a vaporlock type of problem as this happens in the dead of Winter when there isn't any heat involved as the car may not have been started in a couple of months. Fuel seems to come out of the accelerator pump when the gas pedal is depressed. Since it has done this since the car was a year and a half old and I have replaced both filters, rebuilt the carb and replaced the fuel pump, it doesn't seem to be that. When the car is warm, it starts right up. The problem is only when it is cold and hasn't been started in a couple of weeks. Where to go from here???? Ignition all seems good with no other problems. Maybe it is just the nature of the beast.

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Re: Fuel Draining Back? NO!

Post by Mike-Casella »

If you have fuel coming out of the accelerator pump, the only thing that is keeping it from firing off in the cold weather would be a misadjusted choke. That's my take on it.
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Re: Fuel Draining Back? NO!

Post by jsanford »

I think the problem with the AFB is drain-down, not drain-back. The bowls go dry because the gas drains down into the engine over time.

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Re: Fuel Draining Back? NO!

Post by toddallen »

Mike,

There does seem to be a problem with heat and heat soak with the vaporization of fuel on these cars. The problem is not while the car is running, but after the car is shut down.

I wonder if a good precaution would be if after driving around and shutting down the car, one should put the hood up to minimize the heat soak factor?
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Mike-Casella
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Re: Fuel Draining Back? NO!

Post by Mike-Casella »

I'm sure that will help. Think about this for a second. When these cars were built, the only problem they had with the fuel system was the vapor lock. To remedy this, they installed the heat shield on the fuel pump, and that seemed to take care of it. Now fast forward roughly 35 to 40 years. Now we have a much different gas formula containing alcohol which everyone knows evaporates at a pretty good rate when it's subjected to heat. Over a period of time, the fuel in the carburetor tends to evaporate into the atmosphere leaving it, the fuel pump, and the lines, with nothing but left-over fumes. I don't have any figures in front of me, but the underhood temperatures after shut-down are pretty high. Add that to the fact that the hood has all that insulation, which I bet you can guess it's purpose is, yep, to hold the heat under there to help keep the engine warm.

To combat this misery, opening the hood to help get rid of the heat build-up after the vehicle is parked, along with insulating the lines as much as possible will at least put you on the plus side. I had a similar probem with a street rod I had years ago. The engine compartment was just big enough for the monster of an engine I had, and I was experiencing fuel perculation in the carburetors. It took a while to figure out a solution, but the end result took care of it. I saw an ad for an aluminum plate that went under the carburetor, and extended out on the sides roughly an inch, and about two inches front and rear. It was only 1/8" thick and after installing two of them, (dual quads) the problem went away. I just don't know if there is enough room around the carburetor on a Lincoln to be able to utilize one of these spacers.

Sorry for the ramble, but this problem comes up every Summer and it sure would be great to try and put an end to it.
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Re: Fuel Draining Back? NO!

Post by Slick Fan »

Just use race fuel, that'll fix it. :lol:
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Re: Fuel Draining Back? NO!

Post by autostick »

I am responding to this string with a small warning about a part proximate to the fuel pump.
I am tidying up my engine for the LCOC meet. I installed new hood insulation. Much to my chagrin I lifted the hood today and found the entire engine soaked with motor oil, including the new insulation. Any clues on how to clean this mess?
Turns out the small circular cap that covers the fuel pump pushrod has popped off. I have not removed it for 15 years, all I did was change the fuel pump and install a fresh mounting gasket. Does this small cavity develop positive pressure? I was suprised at how much oil sprayed out of that little hole. So this is a warning to ensure this part is secure, I still have no clue as to why this cap went airborne.
The rebuilt fuel pump from Mike Casella works like a charm. The engine seems to idle more smoothly with the rebuilt pump, but there is no change in starting procedure. I agree there is minimal fuel drain-back. We are all spoiled by the quick start of fuel injected computerized engines. I recall cranking some of my old clunkers for several minutes to get them to turn over, depending on climate.

Anyway, give that cap a few taps with a soft mallet and make sure it is snug.
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TonyC
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Re: Fuel Draining Back? NO!

Post by TonyC »

Sorry about the mess. On the engine, maybe degreaser or brake parts cleaner spray will help in the clean-up. I can't speak for the fiberglass insulation, though.

I had a similar problem with that plug some years ago. It didn't pop off all the way, but it was leaking oil in a noticeable amount. I removed it, placed a thin coat of J B Weld around the edges, and re-installed it; no more leaks. Now, I think it's possible to use something else--something that is a bit less permanent, in case you ever have to change out the fuel pump push rod--but I didn't have that issue.

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Dan Szwarc
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Re: Fuel Draining Back? NO!

Post by Dan Szwarc »

Ken, your PCV valve may have stuck closed building up pressure in the crankcase. Yes, oil can be up there. It has to lubricate the pushrod. On California motors, one pours the oil in through that opening through a special CA-only funnel and oil cap.

Do not use brake cleaner to clean the engine bay unless you want to repaint. It removes paint.
You ca use mineral spirits, but be aware it may dull the paint. Engine degreaser probably will work best without affecting the paint.

You can get a new hood pad kit from eBay. I paid about $35 for one.
Here's one: eBay link
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Re: Fuel Draining Back? NO!

Post by autostick »

Dan:
You examined my engine in Columbus so I guess you know I got it cleaned up. I used a gallon of degreaser and a powerwasher in the process. I have a new PCV valve (that of course does not mean it is working) so I will keep an eye on the top end pressure. The other thing I did at the same time was paint the valve covers and install new gaskets. Maybe there was a leak in the old gaskets venting the pressure? Thanks for the ebay engine pad link; I rarely see '63 sets but that does not make sense since all they need to do is cut it to the right shape.
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Re: Fuel Draining Back? NO!

Post by Dan Szwarc »

Email them about a set for a 63. They might be available, just not listed.

When I was judging, I was looking for that glass-fuse thingie I saw on Thursday night. Did you remove it?
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