Leaking AFB Accelerator Nozzle

[Mike Harpster]

I just rebuild my Carter AFB (3721) and now I notice that I get an occasional drip of fuel from both of the accelerator nozzles (both when the car is running and just after is shut down). I have also noticed that no matter how slow I move the accelerator I get a shot of fuel out of the accelerator pump. My understanding is that there is supposed to be a controlled leakage past the accelerator pump such that on very slow throttle maneuvers no fuel is delivered.

The car appears to be running very rich. When I accelerate I now get some black smoke out of the exhaust.

Any thoughts on what might be my problem?

I have been told that I might have my float level too high. What is the recommended float level? I have seen different numbers.

Thanks
Mike
#40893

[Clem Z.]

Re: Leaking AFB Accelerator Nozzle

there should be no leakage even at slow pump movement. drop the the float level 1/16" to 1/8" below the specs for that carb. did you put a check valve,ball,spacer under the nozzle screw

[Mike Harpster]

Re: Leaking AFB Accelerator Nozzle

Clem,

I installed a new pump discharge check needle and gasket under the accelerator pump nozzle. I did not install any ball under the accelerator pump nozzle. The kit I purchased did include a ball for some purpose but I did not remember not removing one when I disassembled the carb and I did not see any in the exploded view diagrams I have of the AFB. I did clean up the pump intake check ball during the rebuild.

Here is some more info that might be helpful. I originally set my float level to 7/32 and had problems with fuel dripping out of the passenger side primary venturi. I then set my float level to 9/32 the venturi dripping stopped.

Thanks Again,
Mike
#40893

[Chris D.]

Re: Leaking AFB Accelerator Nozzle

Pardon me as I often don't know up from down. Please tell me if I have this right. To drop the installed float level, the float dimension is increased the amount you suggest. With a spec of 7/32", should one target 9/32" to 11/32" for the float level adjustment?

Was this practice developed for acelerator pump problems like Mike's or was this targeted at some other issue?

[Duke W.]

Re: Leaking AFB Accelerator Nozzle

Don't confuse "float level" with "fuel level". The float level measurement should be performed IIRC with the bowl cover upside down and the gasket in place, and is measured between the gasket and "top" (which is actually the "bottom" during the measurement since the bowl cover is upside down) of the float, with the float hanging from gravity, the limit of travel being contact between the needle and seat.

The detailed procedure is the '63 Corvette Shop Manual, and a key point is that the larger the "float level" measurement, the lower the bowl fuel level during operation, so if fuel drips out the nozzles after shut down the measured "float level" value should be increased.

Duke

[Les Jacobs]

Re: Leaking AFB Accelerator Nozzle

Mike I rebuilt my 3621 recently and made almost as many mistakes as there are parts. A couple of them might be of some help to you. 1. Accelerator pump- ititially I adjusted the pump incorrectly, and no gas was sprayed when the throttle was slightly depressed. After I corrected the adjustment, gas is pumped under even the slightest throttle movement. The trick was to ensure that the pump stem is under slight compression at the time that the pump rod adjustment is made, so that when the throttle is pressed, the stem moves. 2. Fuel flooding after shutdown: I had the same problem beginning several operating hours AFTER the rebuild. (It was also flowing out of the air horn gasket-what a mess). The problem was the float needle seat was not tightened enough, and after shutdown the pressurized supply line was forcing gas by the seat threads and flooding the carb. ((This also was causing a rough idle condition, and poor low speed performance). Hope this helps. Les

[Clem Z.]

leaking passed the needle seat

some kits have too large a needle seat gasket and unless you get it centered correctly you will have a fuel pressure leak past this gasket. after you assemble the needle/seats and install the floats turn the top upside down and apply about 10 psi of air to the fuel line fitting and squirt some soapy water around the interface of the needle seat and the carb top to check for leaks before you finish assy of the carb. better to find the leak now than after the carb is all together and on the car. i prefer the gaskets that have to be "screwed" onto the needle seat threads

[Mike Harpster]

Re: Leaking AFB Accelerator Nozzle

Thanks for the info...

I lowered the floats and the dripping out of the acceletator pump nozzle stopped. It still appears to run rich during an accel (black smoke). I disconnected the accelerator pump and the engine stumble during an accel so I think it is the accel pump system that is causing it to run too rich. I checked the height of the accel pump shaft and it appears correct. Any thouhts?

Thanks again
Mike
#40893

[Clem Z.]

Re: Leaking AFB Accelerator Nozzle

does it have the correct size pump nozzle and if the pump arm has more than 1 hole is the link in the proper hole? also do you have the correct jets and metering rods?

[Les Jacobs]

Re: Leaking AFB Accelerator Nozzle

Another possibility is that your metering rod springs could also be the culprit. Normally at high vac conditions your springs should allow the rods to be in the full down (lean) position. If the springs are too "strong", they hold the rod "up" and the carb runs rich. One way to check is to physically remove both springs, and see if the carb leans out.