Carter AFB oozing Gas

[knmhobbies]

I just finished rebuilding the stock Carter AFB on my 1965 Buick Skylark. Since then, after I shut the motor off and the car sits for a minute or so gasoline starts slowly leaking onto the secondary butterflies and out the throttle shaft then after a while it stops. This problem may have been happening before I rebuilt the carb I just may not have noticed until after as I was looking more closely at the carb when reinstalling it after the rebuild. It doesn't happen every time and will happen even when the engine is still cool so it isn't fuel boiling. It doesn't leak when the car is running, only after sitting for a moment after shutting off the engine. The floats are adjusted properly and I have double checked to be sure they are. I have tried everything and I am guessing that the fuel pressure may be too high even though I am running a stock mechanical fuel pump. When I pull the fuel inlet line off of the carb inlet shortly after shutting off motor gas does spray with quite a bit of force so that adds to my suspicion that the fuel pressure is to high. My references show that this is a possibility and could cause the leakage and that I may need a fuel pressure regulator. Any other suggestions? What should the fuel pressure be? 3 PSI?

[MagicRat]

Did you change the needle and seat for the fuel inlet?
Otherwise, the floats may be adjusted right but are leaking and partly flooded with gas. Take them out and shake them and listen for a sloshing sound.

Generally, the fuel pump should provide no more than 5 or 6 psi. If it's too high, the pump is bad. Sometimes, these pumps work with a fuel return line, sometimes not. If the return line is blocked off, that could cause a high pressure reading.

The fuel pump is spring loaded on a diaphram, and will maintain fuel pressure in the line. If the line leaks, the fuel pump arm will slowly extend, being pushed by the internal spring until the arm settles on the camshaft eccentric ring. Only then will the fuel line stop producing pressure.

[knmhobbies]

Yes when I rebuilt the carb I replaced the inlet needles and seats for both floats with the new ones that came in the rebuild kit, but the carb still leaked gas. I did suspect that they may not be sealing so I double checked to be sure if that was the problem. I did discover that the replacement needles in the kit were slightly shorter than the originals and thought that might be causing the problem so I put back the old ones just to try but it made no difference. The floats are fairly new. I had already replaced them before because one was leaking and full of gas causing flooding. That is not the problem now. They are dry. I have the float level set at 7/16" and the float drop at 1".

Within a minute or so after shutting off the car gas will start to drip of out of the secondary throttle shaft. If you look into the carb throat you can see gas puddling up on the secondaries apparently oozing out of the venturis. It does leak a little from the primary throttle shaft also but not as bad and has improved a lot since I adjusted the floats the settings mentioned above.
There is no flooding or leaking problem while the car is running it idles and accelerates just fine. The gas leakage does cause occasional hard starting because of the flooding situation caused by the excess gas leakage.

I have been using the Edelbrock Carburetor (Udated version of the AFB) to help trace the problem. According to it, leaking from the throttle shaft and internal carb leaks can be caused by float level and drop, needles and seats may need to be replaced, float leakage, fuel boiling due to excessive under hood temperature, or fuel pressure is to high.
The only one I haven't ruled out is excessive fuel pressure. The guide does mention that some stock mechanical fuel pumps will put out more than 6 PSI of pressure. It recommends reducing the pressure through use of a regulator or by creating a restricted by-pass bleed to the fuel return line. There is no return line on this car just the one line from the tank to the fuel pump. I guess the regulator would be the next step.

[sixty2vette]

I am having the same hard start problem with my Carter AFB, when hot. Did you determine the cause of the fuel dripping out of the secondaries?

[maxwedge]

This thread is 6 yeras old! Start a new one in the future.