hello,
I have an 89 yj with a 4.2L in it. I have put the mc2100 carb on it and upgraded the ignition system(bigger coil and distributor). I have been continually adjusting my timing to find the best running. It idles perfect and seems to run very well. The problem I am having is the hesitation I get when i push down on the gas pedal gas too quickly. I get a really bad hesitation. Allmost a second or 2. It gives me a horrible jerk and makes a big clank under the jeep. Its really bad off the start in first gear but it does seem to happen in any gear whenever i punch the gas pedal. I don't even have to push the pedal to the floor, as long as i press it down quickly i get a hesitation, It won't do it if I very very slowly push the gas pedal down.

Now the one other thing is that it doesn't seem to have a hesitation when I have the choke on full.( i have a manual choke)

Thanks

 

don't worry about any thing, Drive half speed of Gear.

 

I suspect that your mixture is a little weak. If the choke solves the problem then there is a higher ratio of fuel to air. Check to see if the accelerator pump is working - it gives a little squirt of gas when you hit the pedal to take off. If the carb was not new, then it is possible the diaphragm inside the pump is leaking or split and not giving you that all important boost as you hit the gas. Also if the timing is too far advanced (I think) then you can get the same effect. Try backing it of a couple of degrees to see if that works, if not, knock it forward a couple and try again. First though, i would check to see if there is a squirt of gas inside the main choke of the carb when you ope n the thottle. Good luck!

 

your timing is the issue, correct it and you will be good

 

Accelerator pump seems weak. Timing can cause this as well, make sure you have set it to factory speccs, and stop messing with it. If the bolt is tight on the distributor, it cannot suddenly change, unless you have had a camshaft/dist. shaft failure.

Accelerator pump shoots extra fuel into the carb under acceleration. Off idle, or heavy load situations, it squirts extra fuel. there should be extra holes on the arm to the pump to adjust mix. Try that, and see what happens.