Dead spot in carburetor-intermittant

[Ray505]

I have a problem with what I think is the carburetor. These are the symptoms I have noticed:
* When I blip the throttle the engine revs on the first push of the gas pedal but is flat on subsequent pushes.
* When I am in the processes of shifting gears, there is a flat spot, like I'm out of gas, when I attempt to accelerate after shifting. Pumping the gas pedal causes the engine to finally rev up. This does not happen all the time and it happens whether the engine is cold or hot.
* When coasting down a hill, not depressing the gas pedal, the engine won't accelerate when I press the gas pedal. It acts like it is out of gas. After a couple of pumps of the gas pedal the engine jumps to life like it got a shot of gas.
The problem does not happen all of the time and when everything is working properly, the truck runs really well. Also, the engine never cuts out.
I think I may have a problem with the accelerator pump in the carburetor but I wanted to run this past some guys with experience before I start swapping parts.
I have been reading this forum from the start and have used many of the instructions and pointers listed when rebuilding my 1962 M37. It's been a big help and my truck is a lot better for it.
Thanks for all of your help.

[ashyers]

Ray505,
Before you start digging into the carb make sure you don't have any vacuum leaks.

The accel pump on these carbs depends on manifold vacuum. The manifold vacuum pulls the plunger up filling the bore of the accel pump well. When you jump on the gas and the vacuum drops off and a spring drives the plunger down providing the pump shot. If the pump seal or the pump's piston assembly has issues you won't get a shot of fuel. In my experience the pump seals do well unless the carb has been allowed to sit with a dry float bowl. This is certain death for many of the seals. I've seen the pump's pistons get gummed up too ad stick.

Where I live the gasoline is crap, but I drive the truck regularly and the carb has been flawless since it was rebuilt from a pile of parts I picked up at a swap meet years ago. When properly set up the little B&B's are great!

If you do dig into the carb get a carb kit first in case you kill off a gasket attempting a fix. Once you deal with the flat spot it's worth some time to set the governor up correctly. There's a few threads kicking around on the site on how to do that.

Andy

[RMS]

every rebuilt carter I have has a bit of a flat spot. I suspect its the new throttle pump boot. some I have sanded down and the flat spot is smaller but in no way perfect. mostly its when coming down a big hill decelerating get to the bottom give her the beans and nothing. many kits later and the problem persists. so I go at hill prepared as soon as i hit the gas I give her a blip of choke and everything is fine. I've also come to enjoy having to give her a blip of the throttle when pulling away at the lights. its great guys always think I want to race and tear away from me at the lights ...and its good for a laugh if johnny 5.0 is around.

but if you want to eliminate all you Carter carb problems you could try sending it to Charles of toss it in the weeds and get a Rochester or Weber

[NAM VET]

One of the many things Charles T did for my truck, his shop is just a hundred miles from me up in rural NC, was to rebuild my carb perfectly. I think it ran well before I drove my truck up for his work, but my carb works perfectly, no flat spots, starts instantly, no leaks, just plain works. I don't know how to rebuild a B&B, but his shop has the expertise and parts to make them work. If it is the one thing, after checking for vac leaks and timing and fuel pressure, maybe check compression, with a good filter in-line, and it has to be the carb, it might be money well spent. Best wishes, HC

[Ray505]

Thanks for the advice. I'll check everything out, but it looks like it will probably be the accelerator pump. I'll let you all know what I find out.

[Ray505]

Update: Did the vacuum check and everything was fine. I am thinking accelerator pump at this point. When I revved the engine checking the vacuum, the flat spot appeared. Again, thanks for the advice.

[ashyers]

While you're at it verify the float level wet. The latest gas effects it some and I've seen a few "rebuilt" carbs where it was way off.

[NAM VET]

Might check your fuel pressure too, my electric pump was not consistent, sometimes varying by several pounds, too much it will over power the needle and float, and sometimes putting out as little as one pound. I installed an adjustable fuel pressure gage in my line, and it seems to be more consistent now. Plus I could see via my plastic fuel filter that on hot days, it would boil in the filter, so I put insulation on my fuel lines. Charles T rebuild my carb, and with the proper and consistent pressure I have no flare spots or stumbled and it starts instantly. HC
/Users/halcopple/Pictures/Photos Library.photoslibrary/resources/proxies/derivatives/10/00/1007/UNADJUSTEDNONRAW_thumb_1007.jpg

[Ray505]

I took out the accelerator pump and noticed the cup was slightly deformed. It was a little uneven on one side. I plan to replace the pump and see if that fixes the problem. Everything else on the engine checks out. Again, thanks for all the help.