69 340 AVS fuel leak

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69swinger340391

69swinger340391

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My 69 Dart Swinger 340 has been leaking fuel down the secondaries after shutting off the engine while hot. It's got a new fuel tank, sending unit, I cleaned out the fuel tank vent tube, new NAPA fuel pump, filter, and a recent rebuilt to the original Carter AVS.

The motor is the original 69 340 X head, with a slight increase to the cam. All original manifolds, exhaust, etc. While running, there are no leaks, the car runs great. About 30 seconds after shutting off the engine, fuel begins to drip from the passenger side tube above the secondary throttle butterfly. There is a gurgling sound from the carb while this occurs.This continues for 5 - 10 minutes and floods the motor, making a hot restart difficult. Outside temps are only 20 - 40 degrees, motor runs at proper temperature. If I loosen the fuel inlet nut at the carb, The gurgling and dripping stop.

With the throttle closed, the vent cap on the drivers side of the carb opens as it should.

The floats have been adjusted to several different levels, this does not help, and they are currently set to the factory specs.

Removing the gas cap does not help either.

Any ideas?
 
Two things. Make sure the housing for the needle and seat (round brass piece that needle goes into) is tight to the carb top. Make sure the gasket isn't damaged. Float levels are correct as you say. Make sure the needle valve isn't creased or cut.
 
Ut oh, Depending on what kit you bought and what components from it you used. Betcha the needles wont close to the seats. The seats in some kits are shorter than originals. Or maybe it was the needles that were shorter. By the time I whipped this problem I had trimmed the slosh baffles in the bowls.
 
I had it rebuilt by a very reputable local shop. He has attempted several times to adjust the floats and the baffles.

I dont understand why it doesn't leak while running, only after I shut it down. If the needle & seats weren't correct, you would think it would leak all the time.

The driver side has a vent opening, what vents the passenger side? That is the only side that leaks.
 
You may not be seeing the perculating or running over as you say while the engine is running because of the draw of fuel through the venturi's. Also, as RedFish said depending on which kit you have, many of the zip kits listed many different float settings for different 340 carbs based on manual trans or auto trans. I still have and original carb kit spec sheet at home along with the 69 Chrysler repair manual with the right specs in it. I'll check it out when I get home from work and get back to you. Remember that when the float levels are being set, it is necessary to invert the air horn and take the measurment form the far end of the float away from the seat end and measure from the gasket to the float. I'm sure your guy did this as it shows in the instruction sheet, but just thought I'd mention it.
 
Also the vent opening is only for the accelerator pump but does act also as a air horn vent somewhat. It isn't necessary to have a vent on the passenger side as the bowls are already vented. Make sure your float on the side that is acting up soesn't have a pin hole in it casuing it be to heavy to float properly.
 
I've rebuilt quite a few carbs yet still was bumfuzzled for a while in this one. If not for having the original needles to look back at, I might still be scratching my head.
Easiest thing to do would be remove the top and turn it upside down. Get the top of the floats to rest paralell to the underside of carb top and make sure the needles are completely closed at that position.
 
I'm going to open it up tomorrow and swap the driver side floats and needles to the passenger side to see what happens. This should rule out or confirm the defective parts.
 
I swapped the needles, seats and floats side to side, and I still have the same problem, fuel leaking down the passenger side secondary tube after shutting off a hot motor. There is still that gurgling sound coming from the carb after shutting down the motor, and removing the fuel line does NOT stop the leaking or gurgling. I also quickly removed the top of the carb while still hot, and I could see bubbles coming from the primary jets on the floor of the carb. I think that swapping the needles, seats and floats proves that they are not causing the problem. Is this considered "normal" for the Carter AVS? Has anyone experienced this before? Any other advice would be appreciated.

You don't see fuel from the venturi's while idling because the fuel is fed through the idle circuit, not the main circuit.


Redfish: did you ever completely remove the fuel baffles in the carb? What effect would that have?
 
I had to remove the tin slosh baffles and trim them , put them back in. Some corrective bending on the float tangs. Those 2 float to needle hooks were the last pieces to go on. Wasn't sure I could use them for a time.
There is a check ball for accererater pump ?
Correct size ball seating properly ? To give that steel ball a tap or 2 with a drift and hammer can correct a potmetal seat (tip of the day). LOL
Have you attempted to run it breifly and snatch the top off while on the engine. If the bowl is over flowing or the acc. pump is leaking down.. you'll see it.
thinking out my fingers again. Good luck.
 
69swinger,

I am not a Carter guy by any stretch of the imagination (I'm a Holley guy) but since you're are running a stock exhaust heated manifold, it sure sounds as if the carb is boiling out and is need of a thick insulating gasket between the intake manifold and carb.

Just guess.
 
I have to agree with RamCharger. I've had this problem several times over the years with factory as well as aftermarket Carter/Edelbrock AFB's. It's the heat from the exhaust X-over passage under the carb flange boiling the fuel in the bowls. Feel the carb when its perc'ing the fuel and I think you'll find the carb is very hot to the touch. Try running a heat-sink/thick carb gasket or plywood-type spacer under the carb,and see if that helps. To solve the problem in the past, I have blocked the exhaust X-over on several engines ,with this problem ,and it has cured it completely.
 
Redfish: Thanks for your reply. I did remove the top immediatly after shutting down a hot motor, and the fuel bowls appeared to be a little less that half full. This looks like a good level, and doesnt overflow into the carb throat.

I do not have any hooks from the floats to the needles. I have seen them before on other carbs, but there are none on this carb when it came back from the rebuilder. I do have them in my box of original parts from when I rebuilt it last year. Incidentally, the only reason I sent the carb for a professional rebuilt was because the idle mixture screw broke off (it's a left hand thread) and the accelerator pump passages were blocked from 23 years of sitting. Both issues were corrected.

65Val: I did consider the heat from the exhaust crossover. There is only a thin paper gasket between the carb and manifold. I'll try a spacer next. Do you remember what size worked for you? How did you block the crossover? Did you remove the intake and plug it somehow? My heat riser on the passenger exhaust manifold has a broken spring, so last year, I wired the counterweight in the open position and verified by looking into the manifold to see that it was open, and not wired closed.

Thanks for your help, I'll let you know how the insulator works out.
 
Maybe that gasket set up is part of the problem?
My 69 340 with a 4612S AVS carb has a thick spacer type gasket under the carb. I bet that thing is to isolate the carb from the manifold heat.
Might be worth a try.

Good Luck,
George
 
69swinger340391 said:
Redfish: Thanks for your reply. I did remove the top immediatly after shutting down a hot motor, and the fuel bowls appeared to be a little less that half full. This looks like a good level, and doesnt overflow into the carb throat.

I do not have any hooks from the floats to the needles. I have seen them before on other carbs, but there are none on this carb when it came back from the rebuilder. I do have them in my box of original parts from when I rebuilt it last year. Incidentally, the only reason I sent the carb for a professional rebuilt was because the idle mixture screw broke off (it's a left hand thread) and the accelerator pump passages were blocked from 23 years of sitting. Both issues were corrected.

65Val: I did consider the heat from the exhaust crossover. There is only a thin paper gasket between the carb and manifold. I'll try a spacer next. Do you remember what size worked for you? How did you block the crossover? Did you remove the intake and plug it somehow? My heat riser on the passenger exhaust manifold has a broken spring, so last year, I wired the counterweight in the open position and verified by looking into the manifold to see that it was open, and not wired closed.

Thanks for your help, I'll let you know how the insulator works out.
Click to expand...

I used a 1/2" phenolic 4 holer under my Carter. It helped a lot with heat boiling the fuel from the carb base. You might need to modify your linkage for the spacer...I did. I had a fuel leak and consequently a vacuum leak at the throttle shaft. You might have a hair line crack in the base causing the gurgling once the engine is off????? Does it burn rich? What shape are your spark plugs?

I solved my problem by switching to a Holley. I like the idea of the fuel bowls hung on the side of the carb instead of on top of the manifold directly.

Jim
 
65Val: I did consider the heat from the exhaust crossover. There is only a thin paper gasket between the carb and manifold. I'll try a spacer next. Do you remember what size worked for you? How did you block the crossover? Did you remove the intake and plug it somehow? My heat riser on the passenger exhaust manifold has a broken spring, so last year, I wired the counterweight in the open position and verified by looking into the manifold to see that it was open, and not wired closed.

Thanks for your help, I'll let you know how the insulator works out.
Click to expand...

I'd try the 1/2 ' phenolic suggested by NiceFishEh, and with the thick gasket possibly. I blocked the intake crossover with small square of thin sheet metal (furnace ducting works good) over the head X-over ports sandwiched between the intake manifold and the head.
 
Does the choke still work properly with the spacer under the carb, or did you have to modify the linkage?
 
I took the carb off and sent it to PA for a rebuild. It was all hooked up and appeared to be connected properly from what I could tell when I took it off. The new gasket kit (specific to the 4612S carb for a 340/727) contained the thick spacer gasket. This gasket is about 5/16"-3/8" thick, and the kit also supplied TWO thin gaskets; one for above and one for below the spacer gasket. I can only assume it was set up this way originally based on the fact that the carb kit came with all 3 gaskets.
If there is something I can measure for you, please ask.

George
 
Thanks George. Mine is also a 4612, and I found the thick spacer in the box from last year' rebuild. I'll let you know how it works.
 
I ran my SB both ways, without the exhaust heat and with it. Motor seems to run better with the exhaust heat-expect when its over 80 degress outside-here in Michigan thats not too often, even mid summer at night it cools off to the mid- 60's.

I always use a thick gasket under there carb thou. Never had heat problems-other than having to crank the motor for 10-15 seconds before starting once in a while. A small price to pay for have a motor that warms up nice and fast.
 
Yes I did, I think it put alot more tension on the choke plate, making for a richer adjustment,and longer partial choke operation. With the spacer installed under the carb, the choke opens up sooner. Does your fast idle cam have any steps on it? Mine does not, and to me that makes it more difficult to set the fast idle.

For example, when I set the fast idle speed high enough to keep a cold motor running immediately after startup, I will let it run for about 30 seconds then tap the gas, the resulting idle speed is too low, and she stalls. I looked and the fast idle speed screw is still on the fast idle cam, but still needs more fast idle to stay running. Increasing the fast idle makes the start up engine speed too high.

I'm going to double check the choke pull off setting.

Anybody have any luck grinding steeper "steps" into the fast idle cam?
 
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