Lean misfire though carb

[440beep]

So I'm getting a lean misfire through the carb. I thought maybe it was weather related but its not, its happened once in hot weather and once in cold weather (yesterday). The car's a '69 Bee 440 Six Pack, 4:10 gear.

So here's what happens. If I drive the car for a steady length of time at 55-60 cruising mph with the cruising RPMs at roughly 3,500 and then come to a stoplight. From the stop I try and launch the car and that's when it lean misfires through the carb (nice cloud of smoke came out the hood scoop yesterday). Prior to the extended drive, the car launched fantastic and hard from a dead stop. The car doesn't have a vapor separator down by the fuel pump so might the fuel be extra warm as it enters the intake and then detonates because the car was driven hard for that length of time? Total timing if I remember is 37 degrees, perhaps I need to dial it back a degree or two, or get a vapor separator installed, or adjust the accelerator pump cam.

Thoughts on this please....

 

[RustyRatRod]

That will be either a timing issue, or that center carb is not getting a good pump shot.

 

[Meep-Meep]

A lean misfire is really a situation where the mixture to that cylinder or cylinders is so lean that it can't be ignited causing a dead hole. What you seem to have is lack of fuel when the throttle is opened causing just a plain old back fire. I'll agree that lack of proper mixture resulting from a fuel system and intake that is super hot might be a cause. This current gas we have is not at all friendly to carbs, and everything does seem to work well when the carb is getting a supply of cool gas from the tank and the intake is not too hot, but all kinds of bad stuff happens as temps rise.

 

[440beep]

Heck, I switched from the #31 pump nozzle to a #41 for fear of this. I'm hoping tonight to check the accelarator pump cam and maybe mess with that.

That will be either a timing issue, or that center carb is not getting a good pump shot.

 

[67 coronet]

do you eng brake when slowing,or just idle down to a stop?if eng braking you could have a sloppy timming chain.

 

[RustyRatRod]

Heck, I switched from the #31 pump nozzle to a #41 for fear of this. I'm hoping tonight to check the accelarator pump cam and maybe mess with that.

The pump nozzle can certainly be upgraded, but if the pump itself is not working right, that's the source and it should be checked.

 

[bm02tj]

You also could be getting induction between two plug wires and firing a cylinder at wrong time

try to separate wires and have them only cross at 90 degs

 

[440beep]

I normally idle down to a stop, but will occasionally down shift to 2nd gear, but its rare.

do you eng brake when slowing,or just idle down to a stop?if eng braking you could have a sloppy timming chain.

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All the wiring is clean, no spaghetti bowl in there.

You also could be getting induction between two plug wires and firing a cylinder at wrong time
try to separate wires and have them only cross at 90 degs