engine runs rough when raining or damp

[chevyjr73]

i was just wondering if anyone else has this problem but my truck runs like crap sometimes when its raining outside or very damp. i've had two different carbs on there( q-jet and an edelbrock 1406) and its done the same thing with both carbs. have replaced plugs, wires, cap, even put a new distributor in without the esc module and it still does the same thing. almost seems to me as if water or moisture is getting in the fuel. won't water in the gas cause this problem? it will even backfire and pop a little bit until it gets really warmed up but it only does this when it's damp or raining. i'm wondering if the gas tank sitting sideways between the bed and cab with the whole top of the tank exposed could be letting moisture get into the gas. seems to run better sometimes too when i add water remover to the fuel. any help would be appreciated. thanks.

[NeCrOmAnCeR]

Since you say it happens untill the engine gets warmed up. Might look for carburator icing next time it happens. Icing happens due to the pressure drop across the throttle blades and the high humidity like you describe. This is why vehicles used hot air systems from the factory and newer engines use engine coolant pasages in the throttle bodies.

Also let us know what type of intake you are using, when cold fuel will tend to puddle on the bottom of the intake and liquid fuel passing into the cylinders will not burn. This is the reason for the factory exhaust crossover under the intake.

[chevyjr73]

i'm using the stock intake manifiold, egr valve and all. i do have an open element chrome air cleaner on it. maybe i should try switching back to the factory air cleaner? but i know tons of people use the open element air cleaner and i'm sure they don't all experience these same problems.

[jamie72]

sounds to me like a cracked distribitor cap..

[bloertcher]

He's already replaced that,besides,that usually doesn't clear up without either replacement or spraying with a moisture displacement spray(WD 40)