AFB Carburetor Float Question

[Timothy B.]

Re: AFB Carburetor Float Question

Hi Stu,

When you assembled the accelerator pump did you look at the pump check valve to see if it's leaking back, this could cause the problem you describe. I was told to use some auto transmission fluid as this is easy to see if the valve is leaking. Put some in the pump cavity and push the pump plunger down and check the float bowl for leakage. Does the engine bog or hesitate?

To much gas could cause a bog so it may be a good idea to go back to the .028 on the shooter. I am curious about the secondary gas on the manifold you described, can you explain that better.

On the choke, did you reset the vacuum break on the piston. If I am thinking right the electric choke has this also, right?? I don't know why it does not work the same as before but you may consider using the original hot air choke if you have the parts and feel like testing.

Primary jets .104, metering rods 16-389, secondary jets .0689 (I think mine are .070), did you run some small drill bits through the air bleeds etc. I don't think blocking the hot idle compensator is going to give you any problem.

[Stuart F.]

Re: AFB Carburetor Float Question

Tim;

Thanks for your response.

The accelerator pump is a new kit pump, but I had to transfer an override spring to it. The one I used is extra strong as the only other one I had that would fit is too soft. I set it at at 33/64" (high side). I did test the check valve - cleaned it first then used about 20-30 psi air and it seemed to hold. Perhaps I'll try the autotrans fluid again when I open it up.

Off the line, it jumps out and then lays down for a brief moment, as you say, like it's getting a big shot and then going dry (before transition). I agree, I may have gone too big on the squirter, but J.T had a .033" in there and said it worked great. I have a .0292" and a .028" so I'll work back in steps. Also, I will go one more step with the transition springs as that is easy to try without opening it up.

On the choke; I checked all the adjustments even to match my 3721SB on which the electric was working so well. The pull off piston in the 3461S seems a bit looser in the bore (more wear), but that does not seem to be a problem. Yes, I have all the hot air system parts which I may use if my adjustment doesn't help. We are, of course, in the hottest ambient conditions here now.

On the gas wash; it was just evident below the base of the right rear secondary. I should mention, I use a gasket sandwich of 2-340 hp base gaskets with the phenolic 300 hp spacer in the middle. When I went to mount the carb, I couldn't find my new 340 hp gaskets (had a bunch I bought from Doc. Rebuild as theirs seem to be the best), so I reused the old gaskets (a crime I guess, but it wouldn't be the first time). I have since found my stock and intend to change them when next I remove it to make changes. I was pulling a steady 13" hg vacuum, so don't think I had any leaks. However, my idle speed was a little erratic (hunting some). I use a light throttle return booster spring off the bottom of the throttle arm to a small bracket on the top rear valve cover screw for driving as a means to balance the tension on the primary shaft in hopes of keeping wear to a minimum. Crazy I know, but my 63 has never had a good positive throttle idle reset with just one spring (white or black).

I too am running the .104" primary with stock 16-389 rods (w/red/pink springs), but .071" secondaries. I did clean all the air bleeds very carefully as these clusters went through some sort of media cleaning and I wanted to make darn sure they were clean. I probed them, used carb cleaner and air blasted them.

One other thing I'm going to check is the VAC. I put a B28 (236) on it about a year or so ago, and I have found the pieces we get now have a tendency to fail pretty quickly. I recall I had to return several of them that didn't make specs, and one was failed. I got a good used one from J.D. that worked fine, and several more from GMpartsdirect that were good, but I'm paranoid about them.

This kind of tinkering is fun, specially on your Vette that you don't need to get to the Doctor with, Ha!

Stu Fox