1978 F-100, 302 w/ automatic. Stock 2-barrel carburetor.

Since I bought the truck, my accelerator has been hard to push down. When it finally moves, it suddenly gives way and the engine revs up pretty high. Not more than 300 RPM, but I'd like to avoid putting stress on the engine and transmission.

I've tried oiling the accelerator linkages several times, to no avail. The problem also changes with the outdoor temperature, which is strange. I replaced the accelerator spring right beside the carburetor with a weaker one, but the problem is still there. Could it be that the carburetor needs a good cleaning/rebuild?

Thanks.

 

The carb lever moves pretty freely. I think the issue is that the accelerator linkage is too long on the pedal side, so there isn't enough leverage.

 

I had this same problem on a 79 T-Bird with a 302 2bbl. Mine was constant, let off the gas, like a rock to push, then it would break free and like you said, more revs than needed. It drove me crazy. No one could find it. I brought it up to an old retired mechanic one day and the line was, sonny, pull it in my garage. He fiddled for about a half an hour and then I saw the carb sitting on his bench. He took it completely apart, made a phone call to the stealership and sent me after the parts.

What I had picked up was a throttle repair kit. It had bushings and a new butterfly rod (along with a rebuild kit). I winced as I saw him approach my carb with a drill. He mashed the new bushings in, replaced the rod, then just basically rebuilt the carb. Well, the problem was solved. It seems like the butterfly rod wore an oval pattern on the drivers side of the carb and with the return spring on the carb applying pressure, it would kick the rod sideways just enough to cause a bind. The butterflies were striking the inside of the bore. You could not feel it by hand and the pressure applied by hand would move the rod where it should be. The movement was not noticeable and you could not even wiggle it, but the throttle cable pulling back was not enough to override the wear.

If you look down the throttle bore with a magnifying glass, you may be able to see the butterfly marks. Mine did not have any, he told me that he could feel them on the d/s bore with his screwdriver. He replaced everything back with a comment that the 302 was starving and needed a 550 cfm 4bble, ran a hose with a T from the fuel outlet to the tank, started it, crimped the gas line and tuned it with propane. I had never seen this done on a Ford, but I did do it frequently on Mopar products, especially the thermoquads.

I know he changed a few things internally because the parts he replaced did not look like some that he took out, but I can say is that he woke that 302 up in that heavy T-Bird. I know this was a little windy, but.............

 

Hey, that's good advice. I think the carb is all original, so a rebuild might be something to do. Thanks.

 

If you are going to do a rebuild, get an old mechanic, not a parts hanger. Today's parts hangers do not know a damn thing about carbs. The same goes for a distributor. Most do not even know how to set the dwell on them. I laugh my ass off at some of these supposed certified ASC (?) mechanics. Carbs are like automatic transmissions. Yeah, there is how to books, but book learning on these items just does not work. You need to know exactly how the part works as an assembly. Without that knowledge, experimenting is just throwing dollars down a toilet.

I would say that you have a C-4 or maybe an FMX behind that 302 If you change the fluid, look for the magnet. It should be in the pan, halfway up from the drain (If it has one, most truck do). Some asses will put it on the valve body and it will screw it up. All the trash will gather at that point in the body and plug it up. They say it needs to float in the fluid. I just gotta call bullshet on that. I have tore open too many with no two/three shift and found the magnet on the body. You can flush it without a teardown, but it is a bitch.

 

1977/79 T-Bird's have an accelerator cable. F100/150 302's only have it in 1979, prior years use a linkage rod.

See upper pic:

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That is true Bill, but that cable also has a spring in it that puts pressure on the butterfly bore when you try to mash the pedal. That is why you cannot hand feel it. The cable did solve the problem of a sticking dirty linkage but only hid an ongoing problem with the soft aluminum used in the Motorcraft carbs. That is why the repair kit contained brass bushings and o-rings instead of grooved plastic like they used in the Rocks repair kit. Yeah, chevy and mopar had this sucky ass problem too but you could see fuel leakage in the Rocks. The Thermoquads were bad for just having the bakelite center bodies cracking out the back. I saw a lot of problems with them all, but had never experienced something like this out of Motorcraft. That is why I could not figure it out on my own and as I had changed jobs and did not have a garage or time to properly look at the problem.