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4175 Holley fuel leak.

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Old Jul 20, 2021 | 10:33 AM
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From: Loveland
Default 4175 Holley fuel leak.
I am getting a few drops of fuel leaking from the driver side throttle shaft on to the intake manifold. New, needle and seat,,, power valve,,, float,,, seals,,, and throttle shaft bushings. Float adjusted properly. Original fuel pump. Fuel filter and return line original. Engine starts and runs well.
WHY?
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Old Jul 20, 2021 | 11:17 AM
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After the engine has been thoroughly warmed up and shut off, have you looked down the carburetor throat to see if gasoline is dripping ?
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Old Jul 20, 2021 | 11:49 AM
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From: Loveland
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I'll check today thx. I know when the engine is running there should be suctions/negative pressure at the shaft.
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Old Jul 20, 2021 | 12:08 PM
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Originally Posted by kodpkd
I'll check today thx. I know when the engine is running there should be suctions/negative pressure at the shaft.
Not on the top half of it there is not......above the throttle blade there is no vacuum at all......
Fuel dripping from the throttle shaft is always excess dripping from the booster and puddling on top of the blade...then out through the shaft.....
Start the engine and look down the throttle bore at idle......is there fuel dripping from the boosters? If so.....then you need a primary metering gasket. No fuel should come through the booster during idle, and there is no other constant source of fuel in the venturi other than the booster.

Jebby
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Old Jul 20, 2021 | 12:43 PM
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From: Loveland
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I ordered new metering gaskets already. By shaft I mean the throttle shaft where fuel is leaking,,, isn't there suction there?
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Old Jul 20, 2021 | 12:56 PM
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Originally Posted by kodpkd
I ordered new metering gaskets already. By shaft I mean the throttle shaft where fuel is leaking,,, isn't there suction there?
I know what you meant. Think about the throttle shaft and the plates......one half is above and one below. Only the part of the shaft below the plates can have vacuum.

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Old Jul 20, 2021 | 02:43 PM
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From: Loveland
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So if there is higher pressure than atmospheric pressure on top of the throttle shaft you will get air and fuel being pushed out of the shaft bushing gap while running?
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Old Jul 22, 2021 | 02:46 PM
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From: Loveland
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Is there a chance if the base gasket isn't sealed, fuel could leak from there? I'm pretty sure with the engine acting like a huge 327 inch vacuum, sucking air through the carb, the only pressure in the card bore is suction.
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Old Jul 22, 2021 | 02:50 PM
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Originally Posted by kodpkd
So if there is higher pressure than atmospheric pressure on top of the throttle shaft you will get air and fuel being pushed out of the shaft bushing gap while running?
No, but if fuel is puddling on top of the throttle plate when it is shut then it will seep out the sides. The pressure outside the carb is the same as inside the venturi with the blades shut.

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Old Jul 22, 2021 | 02:51 PM
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Originally Posted by kodpkd
Is there a chance if the base gasket isn't sealed, fuel could leak from there? I'm pretty sure with the engine acting like a huge 327 inch vacuum, sucking air through the carb, the only pressure in the card bore is suction.
No, the base gasket has no way to leak fuel. if it is coming out of the throttle shaft then it is dripping out of the boosters like I said. No other place the fuel can come from constantly.

Jebby
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Old Jul 22, 2021 | 06:06 PM
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From: Loveland
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Originally Posted by Jebbysan
No, the base gasket has no way to leak fuel. if it is coming out of the throttle shaft then it is dripping out of the boosters like I said. No other place the fuel can come from constantly.

Jebby
I'm not 100% sure it coming from the shaft. The shaft and the gasket are 1/4 inch apart.
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