Carb Frustration

[DSpringer]

Engine was running pretty good but rich until recently when I started it after it sat for about 3 weeks. Fuel started shooting out the float bowl vent on the side of the carb. Pulled the top, checked the float valve - sealed fine and nothing keeping it from closing. Reassembled, same thing, Tried a top from a spare carb that has the vent hole closed off. Gas streaming down the throat and engine struggling to run. Adjusted the float tab way beyond where it should be (where the float bracket is parallel to mounting face), and seemed to help but still running rough and won't idle worth a darn. Guess she's just hungry for attention. 

[Ken/Alabama]

Sounds like the float may be full of fuel.

[carbking]

A vehicle with an issue may be viewed as a challange or a frustration; and the older I become the more the pendulum moves from challanging to frustrating  There are actually a few television shows more enjoyable than changing the oil! (Not many!)

 

However, possibilities:

 

(1) Defective float valve (you have eliminated this)

(2) Improper float setting (you have eliminated this)

(3) Defective float (easy to check, remove and shake, then submerge in hot water)

(4) Cracked casting (probably eliminated as you changed tops)

(5) Too much fuel pressure

 

Check (3), and if good, a fuel pressure gauge inserted at the carb may tell you something.

 

If too much fuel pressure, possibilities:

 

(1) New off-shore fuel pump

(2) Defective original fuel pump (bypass not functioning)

(3) Fuel tank vent plugged or missing (some were vented in cap, new caps mostly don't have vents).

 

Jon.

Edited December 28, 2015 by carbking (see edit history)

[19tom40]

Jon gave you good information, but not enough detail on detecting float leaks.

 

Boil some water and then turn off the heat, submerge the float in the hot water, a pair of tongs is handy for this task. If the float has a leak, the heat will make the air inside the float expand and you will see bubbles coming from the leak.

 

A leak can be soldered closed, but you are better off trying to find a new float.

[DSpringer]

Thanks for all the advice folks. Didn't mention I also tried another float and shook both of them - empty. I thought about the fuel pump too. I got it new from Sac Vintage Ford - looks just like the original - and have been running it with no problems for two years. As I understand it, there is no bypass, but the spring regulates the pressure. As I understand it, when the float valve closes the spring stays compressed, no fuel gets pumped, and a constant pressure is maintained. 

 

I'll check the gas tank next. Must use a vented cap since there's no vent. Strange though since the weather's been cold I wouldn't expect a buildup of pressure. If nothing else works I'll spring for a fuel pressure gauge. Any idea what pressure I should be looking for?

 

Do your Ford/Holley carbs have a vented float bowl chamber? There's a little knockout on the side of the top piece just to the right of where the fuel line connects that opens to a slot inside the float chamber in the top section of the carb. It's punched out on one of my carbs and not on the other.

 

Stay tuned. I'm going to win this eventually and will let you all know how.

[19tom40]

The fuel bowl must be vented. The Ford carburetors for the 41 and earlier cars had the small cutout on the side of the top piece. The later carburetors used a vent tube inside the the throat of the top of the carburetor. This was done to prevent the airflow from the higher position of the fan from causing a siphon effect on the vent. I am not sure about how the Zephyr carbs are vented.

 

The shaking test doesn't always work, the hot water test does. If your floats pass the hot water test, I would suspect the float valve is sticking or the float is dropping too far and sticking.

 

There are 4 types of float valves in common use: the all metal needle and seat, the metal needle with a rubber (Viton) tip and seat, the rubber ball in a cage and the Daytona Carburetor valve. I prefer the all metal needle and seat. The rubber tipped and the rubber ball types tend to stick after a few years of using gas with Ethanol in it. I don't have much experience with the Daytona Carburetor valve, so I will not comment on it.

 

The float should drop just enough to allow the valve to open. If it drops too far, the needle will stick on the float. Polish the area of the float where the needle rides, so that the needle has a smooth surface to ride on.

 

You can check your fuel pump pressure by using your vacuum gauge. Disconnect the fuel line at the carburetor and connect it top your vacuum / fuel pump gauge. Start the engine and read the gauge. the reading should be around 3 lbs, above 4 lbs expect problems.

[DSpringer]

Boiled both floats, no bubbles. I haven't found a pressure gauge that reads as low as 3 lbs, but the problem may have been excess fuel pump pressure.

 

I have two fuel pumps, one that came with another engine (AC, Made in USA) and a new one that looks nearly identical acquired from Sacramento Vintage Ford, but without any markings. I removed both springs, placed a strip of wood across them, and put a lead weight dead center on the wood. The AC spring was about 1/4" lower than the new one. After replacing the new spring with the old one I haven't experienced the overflow problem, but who knows what new mysteries time will bring? 

 

Now my speedometer is screaming at me. Always something, but it keeps me out of the bars.