Stumble at initial full throttle

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pa karp

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I have an issue with my 340 4 speed. The engine has developed a low speed stumble. It seems to run fine at high way speed.

I have replaced the coil and distributor cap. The ignition has been converted to electronic ignition.

I checked one of the spark plugs, it looks to have normal coloration. Wires are new.

If the car sits and idles for sometime, it will start to lope, eventually will load up and then quit. The carb is an Carter AVS 4611 which is correct for the engine. It has been rebuilt and worked fine. This problem just started.

Any ideas?

Thanks

Pa karp (Curt Rees)
 
While idling take a mirror and look down the carb throats. See if there is any fuel dripping from the boosters.
 
Looks like I have a fuel leak in one if secondary barrels. Carb is coming off.

Thanks for the replies.
Pa karp
 
Looks like I have a fuel leak in one if secondary barrels. Carb is coming off.

Thanks for the replies.
Pa karp
How long has this been going on. I had a Rochester Quadrajet on a 400 in my 68 GTO. Did the same thing...was a leaking needle and seat. After the engine was turned off it would drip fuel until the pressure bled off. The end result was a hole in the #6 piston from an oil pan explosion. Better check your oil that it's not loaded with fuel waiting for the right moment. Mine blew cranking it over at the parts store with a carb rebuild kit in a bag on the front seat.
 
I had the same issue with a avs type carb, couldn't stop it from dripping out of the front barrels. It was leaking by the accelerator plunger due to wear in the bore. I put a Holley on it because I had one, and i didn't ever want to go through that hassle again.
 
I had the same issue with a avs type carb, couldn't stop it from dripping out of the front barrels. It was leaking by the accelerator plunger due to wear in the bore. I put a Holley on it because I had one, and i didn't ever want to go through that hassle again.
 
Pulled the carb, it was fine. Replaced the orange ignition box with the blue one. Engine idles rough and will not idle below 1000 rpm. Timing is set at 12 degree initial. Above 1500 rpm the car pulls hard in all 4 gears. when I shut the engine off, it will diesel. When the car dies at idle, it will also diesel. I am at a loss.

Thanks

Pa karp
 
check for air leak. intake or carb gasket etc. spray some carb cleaner around intake bolts and other areas to see if engine speeds up. good luck
 
It deisels cuz the throttle is too far open. The throttles are too far open cuz the AFR is too rich. The AFR is too rich,cuz fuel is getting into the intake that is either bypassing the low-speed circuit, or the float level is just too high.
To check for a too-high float level,just pinch the rubber fuel line ( or shut off the electric pump), and wait. And wait. And wait.
One of three things is gonna happen as the fuel level goes down.
A) the engine will speed up, then hang there, and then slow down and soon stall
B) the engine will hang there , and then slow down and soon stall
C) the engine will slow down and soon, stall.
In A) the starting level is too high
in B) the level is just right
In C) the starting level is too low
This is only true if the intake is not seeing fuel from any other source besides the low-speed circuit.
Is your accelerator pump check ball or check valve in there for sure? For sure?
 
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