304 idles fine, hesitates on takeoff--until warmed up

[Mbuckley]

Hi there,

I have a CJ5 with a AMC 304 and a MC 2150 carb-55 jets, 1.21 venturi. It starts just fine (cold and warm), and also idles just fine. I can drive about a block with it running perfect, but then things change. After this, when I takeoff from a stop, or give it less than 1/2 throttle slowly while sitting, it hesitates and bogs, forcing me to rev it high and ride the clutch to get it going. Once i get to mid to high RPM range, it smooths out. This ONLY happens until the engine warms up completely, then everything works perfectly.

New accelerator pump diaphram--seems to be responsive with no slack
Checked for vacuum leaks also with carb cleaner--none to be found around carb
Choke is working as it should. In fact, I just installed a manual choke.

ANY help would be greatly appreciated, as this is very frustrating. I do not want to let it idle for 20 minutes every time i want to take it out.

 

[shum8]

Hi there,

I have a CJ5 with a AMC 304 and a MC 2150 carb-55 jets, 1.21 venturi. It starts just fine (cold and warm), and also idles just fine. I can drive about a block with it running perfect, but then things change. After this, when I takeoff from a stop, or give it less than 1/2 throttle slowly while sitting, it hesitates and bogs, forcing me to rev it high and ride the clutch to get it going. Once i get to mid to high RPM range, it smooths out. This ONLY happens until the engine warms up completely, then everything works perfectly.

New accelerator pump diaphram--seems to be responsive with no slack
Checked for vacuum leaks also with carb cleaner--none to be found around carb
Choke is working as it should. In fact, I just installed a manual choke.

ANY help would be greatly appreciated, as this is very frustrating. I do not want to let it idle for 20 minutes every time i want to take it out.

I have similar traits with my AMC 304 , but I'm running an Edelbrock intake and carb.... I also have a manual choke (and love it). On really cold mornings, say 20 and below, full choke with one press of the accelerator and she fires right up. If I don't let her idle for 10 minutes or so, we stumble up the street for a couple houses, but will smooth out soon after. Mine is rather cold natured. I believe it's just the nature of a carbureted engine. If it's not, I need to do some work LOL.

 

[Lumpy Grits]

Change fuel filter and check float level.
CK all bolts etc on the carb and manifolds to be sure they are "tite'.
Also-See how loose the vacuum lines at their fittings are when cold.
Are you SURE the idle mix screws are set the same?
LG

 

[jp360cj]

What kind of choke & how is it set? I have a manual choke and it will sometimes spit and sputter when cold if I don't set the chock correctly.

 

[Mbuckley]

I appreciate the suggestions guys. You know I'm going to do due diligence. Thanks. I'm gonna check timing as well, just to make sure I've got my bases covered.

 

[mtnwhlr]

With a carb it's just the nature of the beast.

 

[Mbuckley]

The choke is one from the parts store with the round black plastic cover.

 

[jp360cj]

The choke is one from the parts store with the round black plastic cover.

But is manual, automatic (thermo), or electric?


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[shum8]

You realize that choke is also a theft deterrent in cold weather...... they’ll drain the battery before they get it started.....


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