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TR4/4A Gasoline in vacuum advance unit.

Merlin63Tr4

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Why is the vacuum advance unit in my TR4’s distributor filling up with gasoline?

I was doing a regular maintenance check on my TR4.
As part of that I was checking the vacuum advance unit for leaks, etc with a Mighty Vac and it sucked a fair amount of raw gasoline out it.

The diaphragm of the vacuum advance unit is not punctured (vacuum reading was rock solid) and the car is running like a champ but this raw gasoline in the vacuum advance unit is very puzzling.

Carbs are Z-S CD175’s, the current vac pipe to the distributor is hard plastic, had the same occurrence with the original metal pipe.



D.
 

poolboy

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Can you describe the location on the carburetor that the vacuum pipe is connected ?
 
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Merlin63Tr4

Merlin63Tr4

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Totally standard.
90º nylon fitting at the bottom of the f
ront carb.

D.
 

poolboy

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...sounds like an accumulation of too much residual gas still in the throat of the carb once the engine is killed.
There's probably too much gas, too high a level, within the carb's float chamber...could be the needle valve's fault or the setting of the float level height.
 
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Merlin63Tr4

Merlin63Tr4

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I'll check the float level.
Car is running great otherwise.

D.
 

GTP1960

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That's a very worrisome thing,( if my mental pic is correct)......gas possibly in the distributor housing? With a hot spark occurring multiple times a second, only a couple of inches above the vacuum connection.

I think you should cap off your vacuum advance until you get it resolved.
 

poolboy

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It might be a good idea to smell the oil on your dipstick for the odor of gasoline.
 
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Merlin63Tr4

Merlin63Tr4

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Oli is fine, no gas smell, level is where it should be.
There is no real way for gas to get into the distributor body.
If the diaphragm gets punctured the engine vacuum would suck the gas back into the intake manifold.

D.
 
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Merlin63Tr4

Merlin63Tr4

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Checked the float level and it was right on the money.
But I also found the fiber gasket under the float valve seat “perished” (pieces missing) and the seat loose.
Fuel probably leaked past the threads and raised the fuel level and caused the original problem.
What is surprising is how well the car was running, spark plugs normal color, plenty of power, etc.


Thanks for help.

D.
 

poolboy

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Good for you, D...Anytime I hear about gas being discovered in a location you would not expect, I suspect the needle valve.
I see those fiber washers on a lot of the carbs I work on; I replace them with the metal versions.
Speaking of gaskets being perished...there is (or was) a batch of float chamber gaskets, not saying they came or come from any particular vendor but referring to Moss part # is 696-080 since I have the catalog handy, that literally began turn to mush upon contacting gasoline..
 
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Merlin63Tr4

Merlin63Tr4

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Yup, installed the metal gasket that came with a carb kit I had. Took the rear carb apart too and found that the fiber washer on that carb was also in poor condition. Must be something in the fuel attacking them. All other gaskets and o-rings looked fine, but they all got replaced anyway.

Thank for the help,

D.
 
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