Can't get her to idle!

[Bad Dingo]

My current big issue with my Jeep is that she won't idle. As soon as I let off the gas it instantly cuts off. I just got this so here is a little history on my observations and what I've done so far...

It ran rough when I test drove it. It idled ok, but you had to give it more gas than I think it should have when putting it in gear or it started to bog down.

When I got it home I noticed a small fuel leak coming out of the diaphragm on the front of the carb (Motorcraft 2150) so decided to do a basic rebuild. I basically changed the gaskets, the diaphragm, and set the float (I used a kit from Mike's Carburetors for those familiar. I heard it was good for novices). After I put it back on is when I couldn't get her to idle at all. Initially I saw that I had a fuel leak coming out of the back of the carb at the base. The kit included a spacer that I put on in addition to the base (after the nuts are on, it leaves me maybe 1/4 inch of thread. This fixed the fuel leak on the carb.

Next I replaced the manual fuel pump. I currently have a clear fuel filter installed and when I would rev the engine I could see the gas spurting into it. But it still cuts off the moment I let off the gas. Doesn't stutter, doesn't bog down, just cuts off.

Next I've replaced the spark plug wires and distributor cap (the plugs to be replaced soon, just having some issues accessing them). I did notice a significant build up of rust(?) on the armature that makes contact with all the plug points on the cap (sorry don't know the tech name for it). I cleaned that up as best I could.

I did replace some vacuum lines. Problem is, when I first popped the hood, I had lines running this way and that, some going to nowhere, some with split-T's with no destination.. complete chaos. I'm familiar with the routing plan for the AMC 304 with automatic tran, (I have a manual) so I did my best to stay close. I got rid of the air/smog pump and I plan on pulling out the purge canister. I'll post my sketch at the bottom. When I started it up this time, she kicked over pretty well, but again, it wouldn't idle. I have pretty much everything accounted for except the air intake assembly is not running to anything except the oil "neck". The last thing is I there is a large port on the top ,front of the carb that I don't know where it goes to (I think I read somewhere that it goes to the purge canister...)

I tried to get a vacuum reading, but didn't have much luck since I couldn't get it to idle at all.

I imagine if it was a vacuum leak that it would have to be a pretty big one for it to cut off so quickly? Possibly a fuel pressure issue?
Thanks for any ideas. The police department I work for runs on 12 hr shifts so I apologize up front if it takes me a few days to reply and update.

 

[elwood blues]

I found you a vacuum diagram, it says it's for a AMC 304 w/ an auto Transmission , but there isn't any difference.

I really think you either have a vacuum leak, or you have a vacuum line hooked up incorrectly. That's the only thing that makes any sense reading all that you have done.

 

[Bad Dingo]

That's the diagram I've tried to go by. The unfortunate thing is that my carb has more ports than this diagram shows uses for. I'll have to switch the E and S ports as far as which one is capped, I've got them reversed.

Aside from around the carb, what other areas are good for vacuum leaks? Like I mentioned earlier it ran, but only 1 step better than before I rebuilt the carb, and I've tried a few different vacuum set ups with not a lot of difference (though I think I'm a lot closer). I did notice to the right of the carb is I think a check valve with a metal line running into the manifold. That line seems to have some in and out play. I think it runs through a cover plate. I'll have to unbolt it in a day or two and see whats under it.

 

[Jimbos76cj]

What carb are you running?How old is it? Did you take the blades off the shafts to clean it? I hear the 2100 is very finicky if you dont get the blades back on it perfect. also if the bushings that the rods go through are worn it will suck air in from around them. have you tried spraying around the carb and intake with carb cleaner or ether if your ballsy, any leaks will cause the engine speed to increase.

 

[elwood blues]

What carb are you running?How old is it? Did you take the blades off the shafts to clean it? I hear the 2100 is very finicky if you dont get the blades back on it perfect. also if the bushings that the rods go through are worn it will suck air in from around them. have you tried spraying around the carb and intake with carb cleaner or ether if your ballsy, any leaks will cause the engine speed to increase.

X2 on what Jimbo said, especially about the MC2100 carb. If you have more ports on your carb than what you have vacuum uses for, just make sure that you cap them off. You can pick up a pack of vacuum caps from any parts place for just a couple of bucks, you'll probably need a couple of packs, because you only get 1 or 2 of the size you actually need per pack.

I'm sticking with my original opinion that you have a vacuum leak, I believe that it has to be with the carb, there really aren't too many other places for vacuum leaks to occur.

One thing I didn't read in your original write-up, have you check or replaced the PCV vavle, that could also cause it, not as likely, but possible.

 

[jasonmark1993]

Almost sounds to me like you aren't getting enough air.

How many RPMS do you have to hold it at to keep it running?

 

[Bad Dingo]

My carb is the 2150.. etching on the plate said it was from a '77 mustang. When I did the rebuild I just tried to stick with the basics as it was my first time. It actually looked pretty clean on the inside.

I'll add the PCV valve to the list of things to replace. When I took it off it did rattle around a bit, which I assume it should be able to do.

In terms of un-needed ports: I don't know exactly what I do and don't need. I will pick up some caps cuz I'm sure they're more reliable than the old screw in the hose deal.

Haven't had a chance to spray around the carb yet because I don't have an assistant handy. I'll have to grab one of the neighbors or drag the wife out there!