Model A carb drips
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Topic author - Posts: 132
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Model A carb drips
I know this is a model T forum, but many of you out there also have model A’s so I have a question for you. I have a 1931 model A with a Tillotson carburetor with a viton tipped neadle. The float height has been set using an outside clear tube and passes the suction test used for NH Model T carbs. The car runs great. However, about five minutes after shutting down after a run of several miles, I get drips out of the carb. This lasts for about two minutes and then stops. The carb does not leak any other time. If started when the engine is cold for a few minutes and shut down, no leaks. Only after driving several miles or more does it drip. Could the engine heat cause the gas in the carb to expand enough to drip like this? Any help out there will be greatly appreciated.
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Re: Model A carb drips
I think it's likely that the gasoline is expanding or even boiling. I know from experience that if you fill the gas tank full on any of the Ford pickups up through 1972 with the tank behind the seat in hot weather, the gasoline will expand and run out the filler cap. This can happen even after driving 10-20 miles. Gasoline does expand when heated, and it can reach the boiling point in a carburetor bowl. That usually happens in hot weather immediately after shutting the engine down. V8s are prone to it, but any type engine can be affected. I believe that fuel sold today percolates and boils at a lower temperature than that sold back when most every vehicle had a carburetor. Gasoline will not boil when held under pressure, as it is in fuel injection systems, and the lower vapor point helps with cold weather starting and running. A V8 engine will flood after shut down if the carburetor boils. It was a problem with cars of the 50s/60s with air conditioning. They'd get so much heat under the hood in stop and go driving that the engine could flood out at a traffic light. Different "summer blends" of gasoline and higher engine idle speeds, big fans with clutch drives and "heat spacers" under the carburetors helped. In the case of your Model A, a slightly lower float level might help. Parking where there's a breeze will help. Putting several gaskets between the carburetor and manifold might help.
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Re: Model A carb drips
Gas that has accumulated in the intake running back down and out. If it is the only time it happens, don't change anything. Sounds like the float level is ok and shutoff valve is working.
I know the voices aren't real but damn they have some good ideas!
1925 Cut down pickup
1920 Dodge touring
1948 Ford F2 pickup
1925 Cut down pickup
1920 Dodge touring
1948 Ford F2 pickup
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Re: Model A carb drips
My 1930 started doing the very same thing. I drained the tank took off the fuel valve inside under the tank. Use very fine sand paper and those cushioned finger mail files that are extremely fine to polish it up, the used EZ lube between shut off handle and housing, and it hasn’t dropped one drop since.
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Re: Model A carb drips
An easy way to check your shut off valve is to shut it off before you shut off the engine. Close the shut off and let the engine run out of gas. That will stop the drip. If the drip returns after the car has been sitting and not running, the shut off valve is leaking and so is the float valve. (Be sure the fuel line fittings and fuel filter bowl aren't leaking, especially at the carburetor end.)
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Re: Model A carb drips
A Model A intake would not likely collect enough fuel to drip after shutting down, unless you are running it on motor oil.
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Re: Model A carb drips
When using a clear tube to check fluid level, beware the meniscus.
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Re: Model A carb drips
Until you get this figured out, be sure you don't park inside an attached garage, especially if you have a gas water heater or any other gas appliance with a pilot light. The fumes can easily cause a fire.
Norm
Norm
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Re: Model A carb drips
Not a A guy but worked on a few. Have noticed a boiling when stopped on one of the few I have worked on. I dont think much raw gas will flow back, but could be enough to leak, especially if fuel level is on the hi side when shutting the motor off after hot. I do know that with down draft set ups There needs to be a tiny bleed hole @ the lowest point so that gas dosent puddle in the manifold & flood on restart. My rajo set up does bleed back some when stopped.
One test- shut the fuel off to stop the motor. Wont be any dripping from a boil. After while open a carb drain, check for dry or wet or filled back up. Turn on fuel valve, looking for drips from a dirty needle & seat. Play a little. The problem will become clear with the process of elimination.
One test- shut the fuel off to stop the motor. Wont be any dripping from a boil. After while open a carb drain, check for dry or wet or filled back up. Turn on fuel valve, looking for drips from a dirty needle & seat. Play a little. The problem will become clear with the process of elimination.
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Re: Model A carb drips
"However, about five minutes after shutting down after a run of several miles, I get drips out of the carb. This lasts for about two minutes and then stops. The carb does not leak any other time."
I know the voices aren't real but damn they have some good ideas!
1925 Cut down pickup
1920 Dodge touring
1948 Ford F2 pickup
1925 Cut down pickup
1920 Dodge touring
1948 Ford F2 pickup
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- Joined: Sun Feb 14, 2021 10:08 pm
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Re: Model A carb drips
When parking any vehicle with a gravity feed fuel system in a garage, it would probably be a good idea to shut off the fuel and let the engine run out of gas and shut off the ignition before leaving it. Ideally, you'd park outside the garage and shut off the fuel and run the carburetor dry, etc, then roll the vehicle into the garage. That's not always possible, but running the engine for a minute or so with the garage door wide open should be safe. The more ventilation the better. Running a fan during the procedure is a good idea. Parking any gasoline fueled vehicle in a garage where a source of ignition exists is not a good idea. Gas water heaters are a source of ignition, as are gas or electric space heaters, certain electric cars, many air compressors, light switches, some types of heating and air conditioning, and many power tools. My preference is to park any and all vehicles and power equipment in an unattached structure located 50 feet or more from the residence.
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Re: Model A carb drips
Model A Tillotson, while be a pretty good running carb on a Model A, are notoriously plagued with leaking along the float bowl seam. They are made of some kind of pot metal that warps over time and it seems that no matter how much you tighten the screws or replace gaskets some will weep as they age. New in box examples seem to work great for a few thousand miles then some of them begin that confounded leaking. I am not knocking the performance of these carbs but that is an irritating feature of some of them. Mike