One day my truck is driving good the next day I start to warm it up for work and it seems to have a hesitation while shifting into second and the truck starts jumping even heard it back fire. I have good spark and fuel pressure. Could it be something with the carb. Its a 78 slant 6 with a 3 speed.

I vote for poor accelerator pump shot. Generally farting & popping back through the carburetor happens when A/F mix goes lean under throttle opening.

Check pump shot with engine off and choke butterfly open by looking down at throttle plate while opening the throttle by hand 1/3 to 1/2 way. One should see a nice strong squirt of gas shoot out into bore. If just a dribble, or weak stream of no doration, it's time for a rebuild kit to be installed.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

Seems to be squirting gas good. Stream looks perfect it started acting up a morning after we got rain. If that matters. I'm thinking just rebuild it and see.

Low fuel level in fuel bowl will cause drivability problems as described as well.

If the carburetor hasn't been rebuilt for some time doing so may be a good plan, and proceed from there.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

"it started acting up a morning after we got rain"

Could be moisture under distributor cap.

Richard

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Part of Tyrde-Browne Racing

With the backfire (which more often than not is due to a misfiring or crossfiring ignition), this (or a similar ignition problem caused by moisture) seems much more likely than the carb. I would wipe out under the cap, and all the plug and coil wires, check for sparks arcing out of the spark plug wires or their connections under the hood at night, and see how that goes.

BTW, my son washed the car a week ago, and washed under the front fenders, and the car stopped dead a few miles later, and then ran fine after a few minutes. We figured he got some water in the ignition area on the right side.

I check the spark its good had some moisture under the cap and wiped it down still didn't work. My vacuum advanced isn't to strong unless I accelerate. I think I have an intake leak would that do it. Thanks for the help guys I just got my truck going a few weeks ago.

No or little vacuum advance when accelerating because of vacuum drop off when throttle plates are opened, particularly when engine is under load such as driving up hill.

An intake vacuum leak probably would not effect vacuum advance if it were correctly plugged into ported vacuum source; that said source being a point above throttle plate. If your vacuum advance is incorrectly connected to manifold vacuum, that is below throttle plate, a massive leak may or may not have some slight effect of vacuum signal to advance pod at idle.

Any vacuum leak will effect idle quality. The bigger the leak the worse the idle quality to the point it won't idle without hot-foot'en it to keep her running until running on main jets at larger throttle openings and higher than idle rpm. As engine rpm and throttle opening increases the proportion of added air via vacuum leak becomes less. Think of difference between squirt gun (vacuum leak) and garden hose (main jets) and the gun's contribution is negligible once hose is opened up.

Keep plugging away at this problem you will get to the bottom of it.

The previous mention of moisture inside distributor cap is a good clue that I did not think of as there was no mention of wet or humid weather previously posted. A slight bit of dampness under cap will cause real rough idle, and poor drivability if the engine will run at all.

Wet or damp worn out spark plug wire insulation will also cause skipping and poor idle as the spark shunts off via leaky insulation to nearest ground rather than jump the higher resistance of the plug gap; resulting random non firing plugs.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

Crap for gas will cause probs. too.

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ifyoubegintothinkyou'relosingcontrol...it'salreadygone

Check your gas cap. I bet you got water in the gas. Buy some water remover and fill it up with premium

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70 Plymouth Valiant 4dr