Sudden loss of power at take off with initial slight press of pedal...need help

Problem:
(This has happened since I've owned the Jeep)(Motorcraft 2100 & 304)('76)
- Happens primarily in the lower gears (not as noticable in 3rd or higher RPM & speed)
- Most noticable when starting in 1st gear from a stop
- When first pushing the gas pedal in feels like there's a catch or binding that you have to push the pedal through and the rest is free flowing (keep in mind we're only talking about a no more than 1/2 inch distance it feels like
- In this gap the engine feels like it doesn't gets fuel or air (which makes it feel like the power suddenly drops of...litterally feels like it would stall if you kept the pedal in that position and didn't keep pushing the pedal through that "zone")
- This problem only seems to happen in gear and under load (does not really exist in nuetral...but I will check that to make sure)

What I've checked thus far:
- I checked the pedal linkage and throttle cable to carb (when disconnected from throttle linkage @ carb the cable & pedal move without any resistance and moves in-and-out freely)
- Engine off & throttle cable disconnected: moving the throttle linkage @ the carb by hand results in no resistance or any binding. It moves just fine.
- Keep in mind I have rebuilt this carb completely 2 times (this has happened during this whole time before and after rebuilds)

Ideas:
I have noticed when engine running there is a good amount of suction and the carb butterfly plate. Could this sucking cause an initial resistance when pushing the gas pedal? Then once it is past its' initial position you wouldn't have as much suction on this area of the plate?

 

There is a separate idle circuit, which cuts out as the throttle plates open. When the plate open enough the idle circuit transfers to the main circuit, via the idle transfer slot.

I would do some simple tests first. You should be able to make the engine stall by turning the idle stop screw; ie you should be able to make the engine run so slowly that it will stall, using the idle speed screw.

Then make the engine stall by leaning out the idle mixture screws. This will show that you are actually running on the idle circuit at idle.

Then, assuming that my accelerator pump and power valve were operating properly, I would look at the air bleeds for the idle circuit and the main circuit were not plugged, and that the idle transfer slot were being properly uncovered by the throttle plate. I assume you did not remove the throttle plates from the throttle shaft when you rebuilt the carb - if you did, the throttle plates could be misaligned with the throttle bore, which would cause the binding (?) that you describe.

The '76 manual is here http://oljeep.com/gw/76_tsm/Section4.pdf with a very good discussion of the 2100. If you read the detailed description of operation, that might give you some insight into where your problem is. The drawings in that manual do not transfer very well; so look at section 1J of the '82 manual at the description and drawings of the 2150. http://oljeep.com/gw/82_tsm/Part 1 Section J.pdf This manual uses line drawings instead of shaded cut-aways, and may be easier to understand.

 

Thanks Tim, I didn't think of that circuit. I will look into this and post the results.

 

My jeep was doing something that sounds like that. Did you check the timing? I bumped mine up a bit and the stutter went away. After you check the carb out like Tim said.

 

What is yours set at now (after bumping it up a bit)?

 

I want to say 12 degrees. I think 8 is stock. I also have a 360. But it did cure the stutter. Mine also had a dead spot to the pedal at 50mph and slight acceleration. Worth a try.

 

I think you just discribed something I'm feeling in the pedal, "dead spot at slight acceleration". That's what I feel as well...always have (with timing set to stock).

 

I'll take a look at how bumping the timing will affect the symptoms I've described. Thanks guys!