I have a 1975 w200, 318, 435 tranny. I gave her a tune up, because everything looked old, and it didnt run the best.

I did plugs, wires, cap, rotor, coil, fuel filter, and rebuilt the stock Carter BBD Carb. here is my prob

It idles great, smooth and quiet, in N you can rev her sky high, and it never misses a lick, however put a load on her, such as pulling out from a stop sign and its all you can do to keep her running. I adjusted the timing a few deg from TDC, either way and nothing helps. I have good fuel pressure on the guage, and have sprayed around for air leaks, and havent noticed anything. I should also say, in Low range i can run her all over, but if it needs to pull(ie, high range), it cant.

I also see no black smoke at anytime, so its not too rich. When I pulled a few plugs, they were plain white, with no shade of anything. It seems like the more I mash on her(after im moving) the worse it gets, I have to lightly rest my foot to go, which is telling me that its lean, however ive messed with the AC pump, and also raised the needles up to richen the mix, and nothing seems to help.


I know this carb is not very popular, but Id rather rule it out, by getting it better, than tossing a different one at it(which I dont have) to find out it didnt work

 

I had a similar experience with a '76 360cid. Turned out it was the distributor cap had carbon tracking allowing the spark to arc over to a different plug on the cap. Idled great but it was all I could do to get it to run down the road. I "fixed" it by taking a screwdriver and scatching up the inside of the cap a bit so I could make it into a town to buy a new one.

As you already have a new one I don't know what to tell you except maybe, somehow this happened to it also. Maybe some type of conductive film on the inside of the cap allowing it to crossfire.

 

I'd like to hear the cure. All the military Dodges were known for this, so everybody learned how to left-foot-brake to keep them running down the tank trails.

 

I had similar problems on a 70 half ton years ago. I rebuilt the engine with some go fast stuff and a new edelbrock carb (hated it) .... same type issues.

As I remember, it turned out to be a vacuum leak on the back side of the intake manifold. Still don't really understand why it would only do it under a load ... maybe the extra twist from engine torque, I don't know.

Also ... consider looking at the 33 year old distributer itself ... not just the cap & rotor. Those things do some weird tricks when they wear out the bearings. Not too pricey either for the piece of mind.

Check the simple stuff again ... good luck.

PISTOL

 

^^^^you beat me to it!!! Could be a vacuum leak, could be the modulator on the tranny, had that happen to my ol ford.

 

There's an old saying that goes "90% of all carburetor trouble is in the ignition system." Coil good? How old is the module?

 

I tried a few different coils, and a known working one. However I never tried the ignition mod. Ill give her a shot and see if it helps anything.

 

No modulators on Mopar transmissions.

I'd bet on the distributor being the problem. I'd also check the airgap on the pick up coil. Lastly, its possible that the ECU isn't healthy or is having ground problems due to rust. The case SHOULD be grounded.