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Old 12-27-2019, 12:06 PM   #1
Merc Cruzer
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Default Fuel Evaporation or leakage from the carburetor

I recently removed the blocking plates from the heat risers, so now the carburetor is noticeably warmer. Would this account for the loss of fuel in the float bowl over a two day period of not starting the car?

Or would it potentially leak down through the jets or power valve?

The first picture is of the correct float and fuel levels. The second picture is after the car has sat for two days. The third picture is of a float bowl with the jets and power valve (the possible sources of leakage).

Just as a further test, I have refilled the float bowl, on the cold engine, to the correct level, with the backup electric fuel pump, I installed years ago (when I first learned about vapor lock), and will check again tomorrow for any fuel loss. The garage stays at around 50 degrees, so ambient temp should not be an issue.
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Last edited by Merc Cruzer; 12-29-2019 at 02:04 PM.
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Old 12-27-2019, 03:01 PM   #2
deuce_roadster
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Default Re: Fuel Evaporation or leakage from the carburetor

I think you have a good idea by watching after it sits overnight. That will tell you if it is leaking internally like through the power valve (if those Merc carbs have one).
Give us a report on what you find! I have no experience with those carbs.
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Old 12-27-2019, 03:13 PM   #3
51 MERC-CT
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Default Re: Fuel Evaporation or leakage from the carburetor

Does it go down any further than the needle valve inlet.
If it does then something lower than that level is the source.
If it does not go lower than the needle valve inlet there is a possibility that the fuel is being siphoned back into the fuel tank.
The fix for that is to insert a one way check valve in the fuel line
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Old 12-27-2019, 03:48 PM   #4
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Default Re: Fuel Evaporation or leakage from the carburetor

Quote:
Originally Posted by 51 MERC-CT View Post
Does it go down any further than the needle valve inlet.
If it does then something lower than that level is the source.
If it does not go lower than the needle valve inlet there is a possibility that the fuel is being siphoned back into the fuel tank.
The fix for that is to insert a one way check valve in the fuel line
The level was between the top of the power valve (shown in the picture) and the bottom of the needle valve inlet. I can also confirm it did not leak out of the float hinge pin opening.
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Old 12-27-2019, 08:26 PM   #5
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Default Re: Fuel Evaporation or leakage from the carburetor

It's not very likely the carb is leaking down internally unless there is porosity in the bowl (very unlikely). The float valve is above the fuel level, and the power valve is not the type like in other carbs with a rubber diaphragm that can deteriorate.
I'm betting it has to be evaporation from shutting off a hot engine. Especially with the amount of ethanol in the fuel these days. Sal
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Old 12-27-2019, 08:51 PM   #6
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Default Re: Fuel Evaporation or leakage from the carburetor

I agree with the evaporation. Not only is ethanol a factor but the overall vapor pressure of modern fuel is much higher than it used to be. That means it evaporates at a lower temp and a higher rate. Fuel injected cars deal with this with their better-sealed fuel systems but carbs have a tougher time of it.


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Old 12-27-2019, 11:30 PM   #7
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Default Re: Fuel Evaporation or leakage from the carburetor

Mine on the 52 Merc leaks down all year round be it hot or cold weather. Unheated garage. There is some external leakage that I have not been able to tell where it comes from. If it sits for a week its a guarantee I will have to prime the carburetor to get it to start quick. Otherwise wear down the battery and starter waiting on the fuel pump to pull gas up to the carb. I know its not normal but I've learned to live with it. I hate to tear this carburetor apart as they have a thin and flimsy little top gasket that is easily damaged.
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Old 12-28-2019, 08:00 AM   #8
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Default Re: Fuel Evaporation or leakage from the carburetor

Another vote for evaporation and or percolating from engine heat after shut down.
I know of several carburetored cars including my 52 Vic that have a real problem .
Worse in hot weather. Love my elect. fuel pump.
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Old 12-28-2019, 09:32 AM   #9
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Default Re: Fuel Evaporation or leakage from the carburetor

MC,
I'm with Sal, a self priming fuel pump helps.
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Old 12-28-2019, 04:47 PM   #10
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Default Re: Fuel Evaporation or leakage from the carburetor

Get a manifold and throw two Strombergs on it and problem solved and you'll never go back.
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Old 12-28-2019, 07:20 PM   #11
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Default Re: Fuel Evaporation or leakage from the carburetor

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Get a manifold and throw two Strombergs on it and problem solved and you'll never go back.
A local guy was having an adaptor made to install the Ford (Stromberg?) type carburetor on his as the Holley "teapot" was not to his satisfaction. I never did find out how it turned out. Mine is not bad enough that I am about to do any modifications beyond possible opening up and cleaning out the carburetor.
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Old 12-29-2019, 01:26 PM   #12
Merc Cruzer
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Default Re: Fuel Evaporation or leakage from the carburetor

Winner winner chicken dinner, the answer is evaporation. I have continued to check for three days now (wanted to give it a chance for a few days, not just overnight) and the float bowl is still full to the correct level. So it is not leaking.

I put the block off tabs back under the heat risers. Evidently, I don't need to heat the carburetor to that level, even in the winter.

I am completing a cold oil change, let it drain over night. This is the first one since I installed the Power Steering unit, since I don't put many miles on the car. Getting the drain plug out is a bit of an issue, clearance with the unit is tight.

Every time I deal with this carb I think of the other options, but never get around to it. Guess I am not ready to give up just yet. I have driven it for 9 years with that carb and she has never left me anywhere, so that just might be the test. Anyway, over the years, I have amassed a nice collection of spare "teapot" carbs for parts and backup. I guess I should look at it as part of the driving/owner experience, of owning a 53' Merc. If I want the modern car experience, I can just fire up the 1970 Cougar that belongs to my wife, and listen to one of her 8 tracks.

Thank you all for your comments and suggestions.
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Old 12-29-2019, 06:36 PM   #13
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Default Re: Fuel Evaporation or leakage from the carburetor

You can always put a phenolic spacer under the carb to minimize the heat transfer to the carb after shutting off a warm engine. Only drawback would be the rod from the manifold choke would have to be lengthened the same amount as the thickness of the spacer.


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Old 12-30-2019, 11:18 AM   #14
JT FORD
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Default Re: Fuel Evaporation or leakage from the carburetor

If you pull the choke all the way closed it helps after shutting it down....
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Old 12-30-2019, 07:14 PM   #15
Merc Cruzer
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Default Re: Fuel Evaporation or leakage from the carburetor

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Originally Posted by JT FORD View Post
If you pull the choke all the way closed it helps after shutting it down....
Mine has the automatic choke.
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