Gents,

My truck has developed a bad habit when it is cold (as in outside air below freezing and engine cold): The accelerator pump arm rubs against the throttle arm hard enough to bind the throttle partially open (NEVER a good situation!). I've removed the carb and verified that everything "looks" right:
1) The throttle shaft is in the right location and doesn't have any side to side movement.
2) The accelerator pump arm pivot is straight
3) The accelerator pump arm is straight (It's design makes it a bit difficult to just "bend" the arm side to side and I shouldn't have to do that anyway...)
4) The throttle arm is straight

After taking the arm off and straightening it out (repairing my attempts at a "field" repair...), verifying the linkage and then reinstalling and adjusting the AP, everything was working perfectly on the bench (kitchen table...), so I went ahead and reinstalled the carb (always fun at 10:30pm when it is 7F outside and the freaking wind is blowing at 30mph!).

By the time I got everything bolted down and hooked back up, the carb had cooled off a LOT, and the linkage was once more binding. I have no doubt that if I bring it in and let it warm back up, it will work perfectly.

So, does anyone have any ideas what could be the problem? Do I just need to say the heck with it and hit the side of that lever with a file to get the cold clearance it just doesn't have? I can't imagine that this is a common problem with Holley 4160 carbs...

Thanks!

 

Its hard to imagine the temperature changing anything on there to the point of what you are saying.. Do you have a throttle cable or just the rod? Sounds more like some lube somewhere is thickening and negating the return spring at that point or close to it.. But thats the thing about not seeing it.. Just bend the throttle arm out a little if its hitting out on the end, or maybe the pin the pump arm rides on is bent.. still shouldn't be affected by temp change though.. just lube it all up and if you need to bend something to get clearance I guess then you do it..

 

That was my initial thought too. But it is rubbing HARD (outside edge of the accelerator pump lever is shiny and there is a shiny spot on the inside of the throttle arm), but ONLY when it is below freezing. When you operate it by hand, you can feel the "grinding" through your (quickly freezing) fingers. The truck does have a throttle cable and it is fairly new and in good shape, plus it pivots on the ball freely.

I think I'll see if I can bend the throttle arm a bit. I guess I could have bent it in slightly the last time the carb was off the truck (about a year ago when I rebuilt it), but the linkage visually looked straight with my naked eye.

 

Never seen that before. You don't have any water in the fuel that is freezing in the pump housing do you? Just a thought.

 

I don't think so. It is a dual tank truck and I always COMPLETELY drain one tank before I switch to the other tank, then fill the empty tank up completely (minimizes condensation if the tank is full). I've done that since I first got the truck, about 16 years ago.

What's weird is everything LOOKS fine. The AP linkage lines right up on the pump arm just like you would expect, the throttle shaft looks good, the throttle plates are tight, etc... But it sure is binding when it is cold!

I was going to take it off today and do some work on it, but changed my mind when I saw the temps: 1F when I woke up and it made it all the way up to 7F today. I've two other vehicles to use, so this thing can sit until the weekend when the temps should be up into the balmy 30F range!