the truck in my sig has a recurring problem when it starts to rain. As soon as it reaches operating temp it idles rough. but after a few minutes it returns back to normal. i have changed alot of things:
duraspark 2 conversion-new module
removed EGR
removed all plastic vac lines and replaced only essential ones with rubber
replaced intake manifold gasket
running the stock 2150 carb with unhooked feedback solinoid
no hot air valve
edit: new cap/rotor/bosch wires
original coil
14K old plugs

 

Rain and rough running usually indicates a secondary ignition problem, i.e. dist. cap, rotor, wires, plugs. High humidity or outright moisture on or in these components can bridge gaps and cause an unwanted path to other components or ground. Why do you think it's flooding?

 

best thing to do is grab a spray bottle and wait until night. goto a dark place, fire your truck up and rev it up. watch the plugs/wires closely for arcing when reving it up. Then spray the wires and plugs with water and rev. If your having an ignition problem, you will see it.

btw, side note: be careful not to stick anything in the fan blade when it is dark.

 

i did the spray bottle trick on the old wires and nothing happened. i sprayed so much water and it still ran fine. also the rough idle doesnt happen when the engine is cold.

 

Then the problem isn't the wires. I'd still say it's electrical. Cheap wires is usually the first cause, though.

 

the only electrical thing left that i have not replaced is the coil.

 

Check out the connections on the coil.. I've had them corrode up a bit.. that could cause some trouble..

 

Rain = high humidity
No warm air tube
This (believe it or not) is carburetor icing
Once the motor gets halfway to warm, it won't idle, stumbles and the exhaust smells of raw gas
When warm it is still idles bad, however drives perfect
Shut the motor off for 5 minutes (allow the ice to melt from the heat of the engine) restart and problem gone
I have seen this problem on dozens of carbureted Ford trucks
Steve G.

 

How do you prevent the carb from icing.....???? I have this same problem with my 84. After a whiile running it in humid conditions, it would run rough, then die on me. Wait 15 mins and starts up running perfect....

 

Are you sure that is not vapor lock? I can't imagine water (or gas) freezing in the carb unless it is actually cold enough to freeze out..

 

Vapor lock is fuel vaporizing before it makes it into the cylinders, this is caused by excessive engine and fuel temperatures.
Carburetor icing is caused by a combination of the low pressure in the carburetor venturi, the evaporation of fuel and high humidity.
This is of utmost concern to carbureted aircraft pilots when they can't pull over to "let it thaw out", thus "carburetor heat"
The warm air tube from the exhaust manifold not only assists in keeping the fuel in an atomized state when the motor is cold, it also helps to eliminate carburetor icing by feeding it warm air.
Steve G.