Idle Down Trouble

[58D_CavScout]

Got a quick and easy (to someone) question about my carb Idle down. I have a stock 304 in my new (to me) 79 CJ7. When I start it idles at about 2k RPM according to the tach. After warming up and tapping the gas it idles down to about 1k. Idles smooth and sounds great. The problem is, that the idle does not stay at 1k after warm. I'll drive around and come to a stop sign and it's back to idling at 2k. Tap the gas, stays at 2k. Really rev the gas and it might come down to 1.5 or 1k if it feels like it. It's almost as if it's sticking and needs a fast drop from high RPMs to break past some threshold and make it down to the correct idle speed. Clear as mud? I'd like to fix this because it's annoying to have to really goose the gas at every stop light just to get it to idle down. I'm sure the other drivers think I'm trying to get their attention...LOL.

I also have a heavy gas smell with no fuel leaks but I'll save that for another thread unless it's related to this problem. Thanks in advance.

Jake

 

[SteelHeadz]

2 possible scenarios. If you have an electric choke, you can adjust it by turning the choke assy. housing enough to prevent the choke Cam from idling on the first notch. it will take a little bit of patience. another one to check is the Return Spring on the throttle lever to bracket. sometimes the spring on the Carburator is not enough to pull back the throttle to it's idle position.. If in fact that the choke is not completely disengaging, it may be possible that the fuel smell is related to this concern due to a rich condition. I hope this helps a bit.

 

[58D_CavScout]

I'll go out and look at it in the daylight and report back. Thanks for the reply.

Jake

 

[SteelHeadz]

I'm curious on what Intake Manifold and Carburator you have on that 304.

 

[58D_CavScout]

As far as I know it's the stock set-up. I do know it's not the stock air cleaner though because I just bought one this afternoon and had to match it. It's my first Jeep and I just bought it about a week ago so I haven't got all the details. The Haynes manual says the Autolite or Motorcraft 2100 or 2150 came on the V8s. I'll confirm it tomorrow though. I guess it might have helped to gather some more details before posting a question here.... I run another forum like this one on another topic and I should know better.

Jake

 

[SteelHeadz]

I forgot to Mention about the Throttle Cable. Check that for binding as well. as far as the Choke assy. is concerned i think you have a manual choke instead of an electronic choke. It's been several years since i pulled my 304 out.

 

[ka041a]

It doesn't have to be the choke, it could be that the float/needle valve is sticking and allowing excess fuel into the venturies. Another possibility is that the idle mixture screws are turned out too far or damaged. both of these possibilities could explain why revving it up temporarily brings the idle down. Hope this helps, john

 

[SteelHeadz]

Start with the basic diagnostics before you get in the technical and more indepth scenarios.

 

[58D_CavScout]

Thanks guys. I was swamped at work today and didn't make it back until late. I'll report back as soon as I can look at it. I really appreciate it.

Jake

 

[58D_CavScout]

OK guys, thanks for the help. It actually turned out to be a deteriorated plug for the vacuum tube that comes out of the back of the carb near the electric choke assembly. I have no idea what this vacuum line is for but the rubber plug that had been installed on it had deteriorated and was leaking. I was just fooling around with the idle down lever and noticed the vacuum leak against my finger.

I can't seem to figure out what that vacuum line is for using the diagram in the Jeep Haynes manual. Anyone have any idea? Thanks.

-Jake

 

[Collin the Hen]

Maybe it's for a vacuum gauge. I don't have a port on the back of my mc2000, so I couldn't tell you for sure. I'm glad you figured your high idle problem, though. I had that issue too. It turned out to be a slightly skewed butterfly valve. :lol:

 

[58D_CavScout]

Maybe it's for a vacuum gauge.

Thanks Collin. Could be. It's a threaded tube so it sounds plausible.