AFB Carburetor Float Question

[Stuart F.]

I'm finally close to finishing my assembly of my dream 3461S AFB for my L-76 63. It's been a long road to recover from my original being stolen off my car nearly 20 years ago. I'm setting this unit up to operate equally well on either 10% Ethanol gas or non-Ethanol (readily available, but more expensive). Got all the right parts going together, but have one last decision to make: I have both the original brass floats which I've tested and appear to be in great shape, and I have a set of aftermarket replacement floats (also, like new). The aftermarket floats weigh in at about 1/2 gram less and are made of a lighter gauge material and don't have the typical shape impressions in the sides that probably add strength in the originals (less fragile looking).

Question: does anyone have an opinion as to whether any advantage may be realized for using one type over the other?

For instance; would the lighter floats be more bouyant and perhaps allow a lower float setting?

Any thoughts?

Stu Fox

[Norm B.]

Re: AFB Carburetor Float Question

Stuart,

Don't think I am qualified to comment on the bouyancy question but it sounds like you have gone to a lot of trouble to recover originality on your car. Do you really want to put this carb on knowing full well there is an "imposter" hiding in its innards? I would opt for the original float for the self satisfaction of knowing it is as back to original as I could make it.

Norm

[Dan B.]

Re: AFB Carburetor Float Question

I've rebuilt more than a few of these over the years and have always used the original floats. If yours are good, don't over think this, install them and set to specs. If you need to tweak the float level later, you have a good starting point. Dan

[Timothy B.]

Re: AFB Carburetor Float Question

Stu,

My vote is always use the original parts, I think you will be fine with either type of gas.

[Stuart F.]

Re: AFB Carburetor Float Question

Thanks for the comments guys. I guess I was just looking for a reason to try the aftermarket floats. I am a tinkerer at heart and using them or not is not a big deal as to me it's not heart surgery to change them back. I already have made several changes that I hope will further improve the conditions we encounter with the Ethanol in the gas.

I like the 3461S a lot as it is the best for my application on the L-76 SHP for which it was originally engineered. It has the right jetting and CFM flow characteristics, i.e. no deflector tabs on the primary boosters and the lightest counter weights on the secondary air valve, etc. The follow on 3720 series carbs seem to be detuned for the L-75 applications. Those of you with 63 L-75's having a 3461S probably have too much carb for the application, and might be better served with a 3720/3721SB unit for ordinary driving. Obviously thats what the engineers thought when they made the changes for 64 and on.

This time around I'm going to a .031" accelerator pump squirter over the stock .028". Although I'm staying with the stock primary jetting, I've changed the transition springs on the metering rods for about 2"Hg quicker pickup. In the secondary, based on my heat isolation installation, I've removed the Hot Idle Compensator and capped off the vacuum port. Besides not seeing need for it on my application, the way it is designed with the heat sink tabs on the sides, which almost touch the secondary boosters, blocks a lot of CFM air flow. I believe that without it and the 3461S primary boosters without tabs probably adds another 50 CFM air flow (650 vs. 600).

Thanks again for the comments.

Stu Fox

[Stuart F.]

Re: AFB Carburetor Float Question

Decided to start with the aftermarket floats because as I looked at the originals I became concerned. This carb was "restored" by a prominent shop and the method they use to refinish the aluminum is apparently done to the brass parts as well. They have a dull finish almost like being acid etched, and were twisted pretty much out of aligment (parallel to side of top plate). So, I'm not too confident in their integrity. They pass a simple leak test, but I want to check them further before I use them. Besides, I really want to see how these lightweights work out.

Stu Fox

[Clem Z.]

Re: AFB Carburetor Float Question

Decided to start with the aftermarket floats because as I looked at the originals I became concerned. This carb was "restored" by a prominent shop and the method they use to refinish the aluminum is apparently done to the brass parts as well. They have a dull finish almost like being acid etched, and were twisted pretty much out of aligment (parallel to side of top plate). So, I'm not too confident in their integrity. They pass a simple leak test, but I want to check them further before I use them. Besides, I really want to see how these lightweights work out.

Stu Fox

where did you get replacement AFB floats because the ones i have seen are not the same as original including the pivot point and float drop adjustment tang ?

[Tim S.]

Re: AFB Carburetor Float Question

Sounds like a neat little project! Please provide more details. I am going to need to go through the AFB on my L76 62.

Tim

[Stuart F.]

Re: AFB Carburetor Float Question

Clem;

I'm not certain of the exact vendor/provider, but I'll try to find out. I got the carb from a fellow NCRS member (a benefactor) who had installed them due to flooding with the originals. He also sent me a bunch of jets, metering rods and parts from the same source, and they are sized/numbered differently than any Edelbrock items. The floats match up well side by side, but weigh in about 1/2 gram less and are made of just plain lightweight brass, i.e. no impressions on sides, just flat. I can't see any difference in pivot point or tang with my naked eye. I will look at them much closer before I button it up tomorrow.

Thanks for pointing that out.

Stu Fox

[Stuart F.]

Re: AFB Carburetor Float Question

Tim;

I'm not too familiar with the AFB on the 62 other than my impression is that it is nearly the same as the 3461S with the exception of the fuel connection and in line filter, and possibly some other connections such as the PCV valve at the rear on the 63, etc.. Does that sound right?

Be glad to share my experience with you and try to answer any questions you may have. I'm very fond of the AFB as I long ago had my fill of complex Holley's and cumbersome Q-Jets. I firmly believe in simplicity and that no vertcal gasket surface should be below the fuel level in a float chamber.

Stu Fox

[Tim S.]

Re: AFB Carburetor Float Question

Tim;

I'm not too familiar with the AFB on the 62

That makes 2 of us Stu! I am interested in your set up due to the fact your car is stock and it sounds like you really expect them to RUN! I am one who likes their car to be stock but run like the devil. Small details in carb, ignition, and valve timing is what really interests me. I'll start a different thread for L76 "demon tunes" rather that hijack your thread.

Thanks,

Tim

[Stuart F.]

Re: AFB Carburetor Float Question

As an update to my thread; I assembled the carb with the original floats instead of the aftermarket pieces. This is the first carb I've ever worked on on my kitchen table as it has just been too hot to work out in the garage for very long. I set the level according to the 63 service manual using a 5/16" drill bit. Actual at seam dimension is more llike 9/32" down at the middle of the float. Even to get there, I had to do sort of an "S" bend in the float arm to achieve this, but I prefer a lower float level.

Installed the carb last night and did my first running test this morning during the cool hours. I forgot how the early AFB's inlet Hex fitting which uses a metal gasket is not too good and, yes, it leaked. It is threaded back to the shoulder, rather than partially with later fittings which use a red fiber gasket that can self center. I replaced the fitting with one from a later model and it worked well (no leaks).

Before startup, I transferred all the dry settings for idle speed and mixture (screw turns) from my 3721SB that I had on the engine, but was surprised that this carb required more throttle opening to maintain a 750 to 800 RPM, and the mixture screws were very sensitive, but I did get a good steady 13" Hg Vacuum at idle (this 3461S has the .035" fixed idle jets as opposed to the .037" of the 3720 series units). I was looking for at least that as I have transition of the metering rods (springs) set for a 7" Hg pickup point (or 6" Hg). which seems to work well. The throttle response is greatly improved over the 3721SB, very crisp.

I believe I have achieved what I'm looking for, i.e. a setup to operate well on the Ethanol laced gas. Can't wait to drive down to St. Cloud to get my first tank of 93 non-Ethanol gas to really see it come alive.

Stu Fox

[Timothy B.]

Re: AFB Carburetor Float Question

Stu,


I am glad to hear everything worked out good for you. AFB's are good carburetors, what type of pcv valve are you running.

[Stuart F.]

Re: AFB Carburetor Float Question

Tim;

I continue to stick with my CV-590 C's (2-9/16" long) replacements as I have a number of them and have never had any issues with them. These are the silver rolled metal kind. I have a black steel (Stanadyne C4TE-6A666-B) and a silver steel 590-TC that I used to use years ago, but after all the discussion you have had about such odd balls, I'm sticking to the tried and true

Stu Fox

[Stuart F.]

Re: AFB Carburetor Float Question

Finally got out for a long "full warm" test run yesterday morning. The 3461S performance is pretty good, but I've still got some issues to deal with. My electric choke doesn't hold in long enough on this carb at any given setting compared to when on my 3721SB, and I found myself having to blip the throttle after initial start to keep it running (like no choke at all). Funny how it should be so different one carb to the other. Also, I got me a big "bog" to deal with right after initial launch from a stop (new problem for me). I may have taken too big a swing at the pump squirter (.031" vs. stock .028"), but I don't think so. The only other thing I did was go to red (pink) transition springs with the metering rods which only pick up 1" Hg quicker. On paper it looked good, but in reality not so. Also, at full warm, my idle speed jumped around quite a bit even though my vacuum was steady at around 13" Hg. I did a few redline runs and noticed afterwards some slight gas wash down on the manifold from the secondary area. I suspect this carb is generally worn a bit more than my 3721SB.

Oh well, back to the drawing board. Might go back to strictly stock on everything to establish a working base line, including re-installing the "Hot Idle Compensator", new base gaskets, and a .028" squirter. The secondary on this unit comes in real quick and smooth - no hesitation at all with the stock (lighter) air valve and larger .071" jets.

Sorry to bore you FI guys.

Stu Fox