Author Topic: AFB Fuel Leak (Read 3596 times)

Bigpig455 · « **on:** November 12, 2009, 12:26:57 PM »

One of the reasons I haven't moved my new acquisition home (65 Gran Sport 401/AFB)yet is a fuel leak from the carb. I've never had an AFB car before, most of my experience has been with quadrajets, so maybe some of you folks will recognize the symptoms:

Start the car cold and shut it off, no fuel leak. Start the car, let it warm up and shut it off, fuel drips off the main throttle shaft at the linkage. It doesn't leak right away after shutoff, it can take 30-60 seconds. It does not leak while running.

If it was needle and seat, I would think it was pressure related and would happen at anytime there is pressure at the inlet.

If it was strictly float level, I would think it would happen anytime, running or not.

My thought is it's a combination of float level and thermal expansion. If I'm correct, the float keeps the level below any vents, etc.. when the fuel is cold, running or not. But when the fuel warms and expands in the bowl on the recently shut off engine, the float level is high enough to allow the fuel to reach the first path out - how that winds up being the throttle shaft I have no idea.

I've got a service manual on order,but does anyone have the float level spec handy? I'll check it next week. I assume there are no tricks to an AFB to removing the airhorn while still on the vehicle...

Has anyone ever seen this before? Am i on the right track?

Thanks, Rhett

WkillGS · « **Reply #1 on:** November 13, 2009, 10:51:35 AM »

Rhett, there's a chassis manual on this site! Go to the 'Electronic Garage' and select the 65 Chassis manual. Carb specs are on page 98.

While it's possible the bottom of the fuel bowl is corroded thru to the throttle shaft, your problem is more likely due to heat and the fuel percolating after shut off. The AFB is easy to work on. Take the top off and take a look.
NAPA did have individual parts avail like top gaskets and accelerator pumps. Basic rebuilt kits are avail elsewhere for $20.

Should a replacement carb be necessary, the 1965 GS automatic carb is #3921. It's very common as it was used on several 65 Buicks with the 401.

Bigpig455 · « **Reply #2 on:** November 13, 2009, 12:05:28 PM »

Thanks for the heads up on the other features of this site, I havent had much time to go exploring....

I'm with you on the percolating/expansion theory, maybe aggrevated by a float level a hair too high. I'll grab the spec and check it out probably monday.

I doubt the bowl has much corrosion or I need a new carb. The previous owner put too much work into this carb (re-anodized everything!) to start with a lousy core. I'll let you know.

Rhett

nut465gs · « **Reply #3 on:** November 13, 2009, 12:32:04 PM »

Rhett,

I would recommend that you take the carb off and work on a bench. Too many little parts that can fall down into the intake. Like Walt said, the AFBs are relatively easy to rebuild. A rebuild kit will have all the exploded views to help you with taking apart and putting back togeher. Good luck.

John

Bigpig455 · « **Reply #4 on:** November 23, 2009, 12:01:02 PM »

Tackled my carb yesterday - all was going well until I tried to unscrew the idle adjustment stop screw and the whole threaded part of the throttle body fell off in my hand! And it was an original 3921 carb....

My next question - does anyone have a 3921 AFB housing for sale? If so, drop me a line at btrue@travelers.com

Thanks, Rhett

Chris · « **Reply #5 on:** November 23, 2009, 03:32:48 PM »

In case you get desperate..

http://cgi.ebay.com/ebaymotors/Carter-AFB-4-barrel-Carburetor-3921S-1965-Buick_W0QQcmdZViewItemQQhashZitem3357c03e5eQQitemZ220515548766QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories

Best of luck

Chris

Bigpig455 · « **Reply #6 on:** November 23, 2009, 04:41:54 PM »

Spendy, but I'm kinda up against a wall.

Rhett

Chris · « **Reply #7 on:** November 23, 2009, 05:02:05 PM »

Rhett,

Give the guys here a chance to look around first and of course you can consider the Ebay carb if no one can turn anything up for you.

I agree that she's pretty expensive and honestly you might want to consider sitting on this for a while until one turns up (they pop up on a regular basis on Ebay).

Chris

WkillGS · « **Reply #8 on:** November 23, 2009, 05:03:42 PM »

That one has the right number, but the throttle linkage is wrong. What's up with that?

Robk · « **Reply #9 on:** November 23, 2009, 06:44:55 PM »

Rhett,

I have a 3921 you can have. It's a little beat up (dirty one on the left in the photo). Only problem is that I have to catch a plane in the morning and wont be back until Sunday. So if you can wait that long, shoot me a PM or an email at keenafamily@mchsi.com with your mailing address and it's yours.

Rob Keena

Robk · « **Reply #10 on:** November 23, 2009, 09:15:05 PM »

oops. I mean the dirty one on the right.

Rob K

Bigpig455 · « **Reply #11 on:** November 24, 2009, 02:59:43 PM »

Thanks to all for your input, makes me feel a little better about my ham-handed mechanical skills

Rob - I am interested in your carb and would be happy to wait until after the holiday.

I'll keep you all updated on my progress and try to post some better pictures of the car after it's cleaned up. In the meantime, here's a shot taken during my short drive the other day.

I wasnt looking for a 65, I was really looking for a 70-71 stick car. But once I saw this car I was tripping over my own feet to buy it, before I even heard it run.

However, my family did have a 65 Sportwagon as I was growing up. And when I slid behind the wheel of this car I had a tremendous rush of familiarity - the knobs, the speedo, the radio, the color of the turn signal indicators.....I think I understand a little better now..

Happy Thanksgiving -
Rhett

Doc · « **Reply #12 on:** October 16, 2010, 07:52:52 AM »

If, I ever find that car sitting somewhere , I am gonna steal the wheel well moldings off of it....