Sudden Idle Issue

[97XJSP]

long story short, i was driving my truck in the snow today. ran flawless! i was leaving the woods and had to work the engine pretty hard getting out of the field. when i got to the bottom of the field, i noticed the truck was stalling (much like running out of gas which i've done since the guage is way off.) shut it down thought maybe it was hot. started it back up no dice. ran fine with 1/4-1/2 choke. drove to get some gas, filled it. no change. runs awesome down the road once i get passed 1/2 throttle or so. from searching seems like it could be an air leak or lean idle. i'm puzzled by how fast it happened, almost immediately while i was driving. my truck has the holley carb... i found a needle screw with a spring and seal that is down low on the carb, near the back on the side, facing the valve cover. took it out, prayed cleaner in the hole etc. put it back in, screwed it way out, virtually no change in idle. i'm not sure if it is in fact the idle screw or not, maybe someone can confirm. any way, sorry for the scrambled post, i'm in a huge rush right now though. any ideas on what to try next? i've only worked with carbs on small engines but i can learn pretty quickly.
Thanks!

[vrod02]

I installed a clear fuel filter to monitor fuel pump pressure and to see how much crap was in the lines before fire up. At low idle I was not getting enough fuel, turned out to be an air leak,fuel line, on top of the fuel tank.
I've also heard about sock filters inside the tank being an issue.

[97XJSP]

yeah, i've got a clear filter also, just before the carb. it's full so theres plenty of gas... it seems like a lean mixture issue but i had been driving for over an hour with no problems then all of a sudden... low, dieing idle, skipping, backfiring while coasting, etc. it will idle just fine with about 1/4 choke though... goes fine and i can turn off the choke once i get up to cruising speed too... i don't know what to start looking at next?

[vrod02]

You might want to check the points and cap. I ALLWAYS start there even when I think its fuel related.

[vrod02]

wanted to add but could'nt figure out the edit button, been awhile since I've been here. My port engine on the houseboat had simular issues this summer.Everyone and there brother sayed carb issues. It was moisture under the cap! Would not idle under 1200 without choke assistance. It should be sealed just sayin easy check.

[randyscycle]

If you have to use the choke, that means the engine needs more fuel. By applying more choke, you are cutting off the amount of air getting into the carburetor.

Look for:

Vacuum leak

Carb jet stopped

Fuel pump/line issue

After those check out, then move on to ignition, or other things. Just attack it systematically and logically and you will find the problem.

[97XJSP]

ok, i've looked around a bit but i'm not sure where to check for vacuum leaks... there is a mechanical vacuum pump on the fuel pump right? i'm assuming all that stuff has nothing to do with the carb... since i haven't really done much work on the engine since i bought the truck, i'm thinking i should just pull the carb and clean it out, maybe put in a larger main jet? i've read they are pretty lean stock. in the mean time, i'm still trying to figure out why it would have happened so quickly and not progressively over time... makes me think plugged jets but the filter looks pretty good.

[97XJSP]

also can someone verify that the needle i adjusted near the bottom of the carb, facing the valve cover is in fact the idle mixture on the holley carb? can i run some compressed air through that hole to try and clear it if there is something plugging it? and perhaps a brief explanation of the curb idle vs. fast idle screws. i've tried searching for this but didn't come up with much. i know carbs are pretty simple once you figure it out but i haven't been around long enough to have much experience with them. i'm spoiled by fuel injection on the other jeeps.
Thanks

[brute4c]

That screw facing the valve cover is the mixture screw.

Vacuum leaks can be in any of the vacuum lines from the ignitor housing back to the front drivers side of the head fitting to the vent on the fuel pump and the vacuum pump lines.

[97XJSP]

ironically, after posting i went out and started the truck to look for vacuum leaks. i let it warm up and pushed in the choke... same problem. so i kept looking for leaks. everything looked good so i threatened the truck by fitting a wrench for the carb bolts. tried it one last time and it was normal! no idea what it was or if it will come back but the truck is idling fine again. it still has a slight hesitation just off idle without a slight amount of choke but it's much better... maybe there was moisture in the gas?