Carter AFB nozzle drip
 

My son has a 65 Tempest with a stock (other than a RA3 cam) 400. He is running a Carter AFB (don't know the carb number, but its the stock type for 64-66). Recently, it has started flooding, and after you shut it off, it's dripping out the driver side (looks like from the throttle linkage but I'm not sure). When you look down the barrels, it's dribbling from the primary venturi boosters on both sides. We checked the fuel pressure (4.5 psi), floats aren't damaged, checked float level, float drop, needles and seats (they're only a couple years old), and made sure the air passages were clear. None of this made any difference. Carburetor are my weak point...

Any suggestions are appreciated. Eventually it's going to get a Quadrajet, but that's not in the cards right now.

Thanks,
Importsmasher

Both sides acting up is odd with that carb.

Try setting the float level 1/16” lower and see what that does for you.

Check for usage of viton tipped original style inlet needles and seat.
Do NOT use the "lift clip" on the needles, they may cause binding on the float arm if they sit too tight on the end of the needles.

The disc style inlet valves are notorious leakers, avoid at all cost.

And, from the 1966 Tempest Shop Manual:

Fuel tank venting or not? .. May be engineered to vent but vent caps can fail vent lines get clogged with rust / mud dabbers.. one quick easy test is as soon as you park and shut off quickly take fuel cap off and listen for a rush of pressure out .. right after cap removal observe drip or not..

Excess pressure will blow by a good seat and float adjustment

Sounds like the fuel is boiling in the bowls due to heat soak. New fuel does this, especially in hot weather. If it's not doing it while running at idle, this is likely the issue. You may need an insulated carb spacer or a vapor return set-up.

It does it at idle, and whether the engine is cold or hot. It stalls at idle; that's what prompted us to start looking and we discovered this issue.

Importsmasher

One other way a carb can flood at low speed even when the float adjustment is correct is the seat isn't tight in the carb body, or the gasket between the seat and the carb body leaks, and bypasses the needle valve. It's not real common, but I have seen it over the years.

Ok....update. we dropped the float level 1/16 inch. The needles are the viton tipped ones, in perfect shape. I removed the lift clips. I verified the fuel tank vent is clear. It still drips, but only from the driver side (for now, lol). It's a beautiful 70 degree day, so I don't think heat soak is an issue, plus it did it while cold.

Any further suggestions are appreciated!

Importsmasher

I forget is it easy on a AFB for a float to rub on anything to hang it up? ... I would try lowering a bit more since it seemed to help already.

I agree. Also thanks for the additional info. It's not heat soak or percolation since it's doing it cold while running. A float could be hanging up or a hair too high still. Also, what is the fuel pressure? Many new pumps are way out of calibration and put out 8-12 psi when the max should be about 5 or 6.

Thinking back on when I ran 2 aftermarket AFBs and as posted I did have a float hang up once after having it apart .
The ears on each side of the float where the pin goes thru had spread too wide and was rubbing on the side of the fuel bowl .

I have an AFB as well i was fiddling with. i noticed it was dripping fuel out the boosters on the primary. i thought that was odd too. I took out the boosters and made sure to use the wire from a zip tie and push it through the small pipe. also compressed air both of them. I also noticed that if my idle screw was too far in this could cause this but i may have something else going on with this carb. i tried compressed air in the idle mixture screw holes when they were removed just to be sure no clogs. also when it comes to the those AFB's the float settings are not the same as the edelbrock 1406... (pretty sure on this) at least the 9000 series carbs. maybe yours is ? here is a manual from back then. my initial float setting was 10/32. https://www.carburetor-parts.com/ass...ZSXJ6-457ywek6

This link to the troubleshooting section of my website might explain the OP's comment about linkage leaking:

https://www.thecarburetorshop.com/Tr...g.htm#Fuelleak

Now a bit more about understanding the problems with the Carter AFB.

The term "Carter AFB" imparts almost as much information as the term "I saw a red car" ! What brand was the car? What size engine did the car have? Was it a convertible? And much more.

Carter produced 505 different type AFB carburetors, including 70 different for Pontiac, in sizes from 380 CFM to 938 CFM.

At least 5 different floats were used, each with different buoyancy characteristics. I won't even guess how many different fuel valve orifices were produced.

Guess what happens if you put mis-matched float and fuel valve orifice combinations together.

Two major problems with the Carter AFB are: (1) the commercial carburetor rebuilder, and (2) generalized tuning calibrations published on the internet.

Discussing number 2 above first: there are a number of different float settings that were used for the different AFB's, in fact some AFB's used a different setting for fuel valves with neoprene tips than for fuel valves with Monel steel tips. The generic rebuilding instructions included in the cheap (you get what you pay for) FLAPS rebuilding kits are just as bad. The correct calibrations are published in your Pontiac service manual for your SPECIFIC carburetor.

An example of number 1 above:

We used to buy Carter (Pontiac) AFB numbers 3300s and 3326s in quantity, as these, with very simple modifications (plug the HIC port, and install a throttle positioner screw) made great aftermarket carbs for Pontiac enthusiasts wishing to use dual quads. If we bought 10 rebuilt carbs, generally we had enough CORRECT parts to build 6 CORRECT carburetors.

The mantra for the commercial rebuilders seems to be "it physically fits, it must be the right part".

If you take your AFB apart for rebuilding, verify that the parts are correct.

Just for the record, I have been running dual Carter FB's on my shop truck for more than 30 years. The only issue in that time has been when we had factory A/C installed, the A/C shop had the truck sufficiently long looking for parts that one of the floats stuck from the gooey residue created by evaporating modern fuel.

Jon

Thanks for the input! We found the driver side needle valve seat was a little loose. We checked, and there is no evidence of the floats hanging up. We reassembled it, and the boosters are no longer dumping fuel! No more drip from the throttle linkage. No more flooding!

So again, thanks for all the input; we seem to have solved the current issue.

BUT....this brings me to an ongoing (maybe related, maybe not) issue we've had with this car. It doesn't like to idle below 1000 rpm. If I turn it down using the linkage screw, it will start to run rough, and if you rev it, it stalls when the rpm comes back down. I set the idle screws at 2 turns, and played with the large screw in between (idle air bleed or something) to no avail.

Im attaching a couple of pictures of the carb. I dont have the carb number, but it's a Pontiac carb; the same carb as I have on my 66 GTO.

I should probably also point out that I rebuilt this carburetor a couple years ago, using a Napa kit. Floats are brass; appear to be original, and don't leak. I used compressed air to make sure all passages are clear.

Importsmasher

You might try lightly bottoming out the idle mixture screws to dislodge any crap in the needle orifices in that circuit, then backing them out 1 1/2 turns to start the adjustment procedure.

BTW, there is no specific setting, I see people all the time trying to count the turns out from bottoming out those screws. When they count the turns they think they have the adjustment correct, not so. You can get a rough setting by doing this procedure enough to start the the car after working on it.

You set those screws for the best/smoothest idle by adjusting one then adjusting the other to get the smoothest idle by alternating between the two likely at least 3 times or more.

Over more than 50 years of twisting wrenches I just lay my hand on the engine and adjust the mixture screws feeling for the smoothest idle by vibration. You know when you get it right by feel. Of course the rest of the engine needs to be working properly and the mixture screws are the final thing in a tune up to get the engine as smooth as possible. Adjusting the mixture screws separate's an alright tune from a great tune up.

Stick cars just go for the smoothest idle in neutral, automatics I like to do with the trans in drive, wheels blocked and parking brake on. You're trying to duplicate the car sitting at a traffic light with the brakes applied and you want the best smoothest idle. If you have to reset the curb idle speed, you need to reset the mixture screws each time you adjust idle speed, up, or down.

If you're having trouble below 1000 RPM it's very likely that the idle mixture is off, but vacuum leaks will also cause similar problems causing a lean idle mixture, usually turning the screws with little, to no change, may be a vacuum leak symptom.

:2cents:

That carb appears from the pictures to have:

(2) idle mixture control screws
(1) idle air bleed screw (the one in the center)
(1) fast idle screw (the one on the linkage)

There is no curb idle screw. The screw on the linkage should only be used to control the fast idle (engine cold) RPM.

Without knowing exactly what carburetor you have:

Many of the Pontiac AFB's with no curb idle screw had suggested INITIALsettings (engine at operating temperature) as follows:

Idle mixture control screws at 1 turn (2 1/2 turns is the maximum) (with the RAIII cam, I would suggest 1 1/2 turns starting point)
Idle air bleed screw at 1 1/2 turns

From there, as Sirrotica posted above, it is trial and error

Something to try would be run the engine at a fast idle, maybe 2500 RPM, then manually close the choke butterfly. The engine should slow. Release the choke before the engine stalls. If there is crud in the idle circuit, this will sometimes clear it.

Jon

That screw by the linkage isn't the fast idle screw (the fast idle screw is actually stripped out, but cold idle is a separate issue for another day). It is an idle adjustment that I believe someone added, as my GTO does not have this screw. I can't get the engine to idle (I probably should point out that it's a manual transmission) unless I turn this screw. If I back this screw out, I can't get it to idle using the mixture screws and the large middle one. I will try your suggestion using the choke. I tried Sirrotica's suggestion of bottoming out the mixture screws (and the big one). I realize that the suggested settings are a starting point. The engine was recently re-ringed, plugs, wires, etc. are new, point dwell is correct, timing is correct, so I really believe it's a carb issue. I just can't seem to get a decent idle.

Importsmasher

If that is a curb idle screw such as most AFB's use, then turn the idle air screw all the way closed, and set the idle using only the idle mixture screws and the curb idle screw.

If you have a big cam then the idle air screw becomes an adjustable idle air bleed.

If you have a fairly normal cam, then leave the idle air screw completely closed, and use the curb idle screw.

Jon

Thanks for all the input! We turned the center screw all the way in, and set the idle with the linkage screw. Car is running much better and idles now too!

Importsmasher