Runs rough & dies when engine is warm help!!

I have a 75 cj5 with 258 I6.

It starts and idles great at first but after the engine is warm it stumbles really bad. It also dies while I'm slowing to a stop almost every time.

I can turn it off and come back a half hour later and starts up and idles great but after a few minutes its the same thing all over again.

Any help would be great.

 

Choke opening? Staying closed will do this.

 

not sure its electric choke. how would i check?

 

Run it with the air cleaner off and watch the thoat of the carb. As it warms up the butterfly should open.
With a cold engine you step on the throttle to clse/set the choke and give it a squirt of gas to start it. as it warm up the spring in the thermostat heats up and opens the choke. When cold and with the choke set you will not be able to see into the carb. When warm, the butterfly opens and you should be able to. You may have to bump the throttle a little to get it to release after it warms a little, just like when you hit the gas to slow down the idle as it warms up.

The choke themostat may be bad and not opening. A new electric one is about $40. It also may be just a bad ground or no power to it.

 

Had the same issue on my 74 304. Turned out to be the choke would shut instead of open during acceleration.

 

thanks for the info guys ill check and see tomorrow

 

Check the flaps on the air cleaner too. My wifes waggy the doors would close once it got warm and run like crap because it couldn't get enough air. Vaccum lines were on wrong when we got it.

 

I think im gonna say screw it an swap in the 2100 autolite

 

Motorcraft 2100 is a great swap. Used to be a bunch of info here, still should be. Initially a pain to get the carb right, but once you do you'll not have to play with it again for a long time. Some say the Holley 2300 is better, some the MC2100. Either is a step up from what you have. Make sure you get the right venturi size carb, if not it will never run right. look for 1.08 on the drivers side of the bowl. Early fords and AMCs had them. My 79's had 2150's. Wifes' waggy came with a spare, I looked it up and it is a 1976 Wagoneer carb. Hers is an 89.

http://www.earlycj5.com/forums/search.php?searchid=749162

 

Avoid the 2300 - lots of changes needed to make it work well on a Jeep.

The 2100 is a fine carburetor; I put one on my pickup. However, it's an appealing swap if you have the troublesome Carter BBD 2V carb which was used on the later 258. The '75 258 will have a 1V (one barrel) Carter YF, which is a fine carburetor. Using the original 1V manifold, I don't see a lot of advantage to using the 2V 2100 over the original YF.

Have you done a complete tuneup on this Jeep? Have you rebuilt the carburetor? If you have an EGR valve, you can remove it and clean it with a wire brush, then put it back with a new gasket. A dirty EGR valve will stick open and cause a rough idle.

I agree that you need to check the function of the choke. If the choke is not opening, the engine will not run right when warmed up. The choke uses hot air piped to it from a stove in the exhaust manifold, and unless that system is working, the choke will not open fully.

I think it's more likely that you have leaky manifold gaskets. The intake and exhaust manifolds on the 258 are often leaky. When the intake manifold leaks, the mixture becomes much leaner, and the Jeep may not run well once the engine warms up and the extra-rich mixture from the choke goes away. Exhasut manifold leaks are also a common problem on these engines, and must be dealt with to prevent burnt exhaust valves.

A leaky carburetor base gasket is another possibility.

Do you have the factory service manual? The factory manual will help you a lot.

 

the PO but a 2bbl weber 32/36 with electric choke on it,

i got a autolite 2100 at the junk yard today for $21. Went to but the adapter for the manifold at the parts store but an other customer there said he would sell me his that came with an almost new holley 2300. Looks pretty nice compared to the autolite but im thinking I should rebuild the 2100 and put it on my jeep. here are some pics of the two what to you guys think.

 

I think you should keep the Weber and solve its problems. Substituting the 2100 for the Weber would be foolishly trading one unknown for another. The Weber will work well if set up right.

Forget the Holley. Way too much carb for a 258. Unless modified a lot, they are terrible on the trail. Plus this carb has a center pivot float, which will flood out badly on hills.

Plus there's no guarantee that the problem comes from the carburetor. Diagnose your problem first, then replace parts.

 

Yeah your right the thing is I'm deploying to Iraq this fall and when i get back the tubs coming off and I'm hoping to fix everything then. Do a NP435 swap, fix the rust holes, paint, put a new suspension under her the whole nine yards ya know.

I was just hoping to drive it all summer before i go.

So how would i diagnose either a intake or exhaust manifold leak?

By the way I'm new to carbs and jeeps in general so this is all pretty new to me.

 

Thanks for your service and stay safe.

Is the Weber still on the Jeep? Have you investigated the choke performance? Since this Jeep is new to you, have you done a complete tuneup?

More about the symptoms. This is a '75, and came from the factory with the troublesome Prestolite electronic ignition. Are you sure this is a carburetion problem and not an ignition problem? Does the engine start to run bad as it warms up or does it just die?

Do you know where these parts are on the Jeep and how they function?

Check for vacuum leaks (intake manifold, carb base) by inspection, by listening, and then by spraying carb cleaner around while the engine is running. A leak will suck in the carb cleaner and the engine will run faster. Check that all the other vacuum hoses are connected correctly.

A leaky exhaust manifold will be noisy. You can listen around the manifold with a mechanic's stethoscope or a piece of rubber hose in your ear (careful!) for leaks.

 

This is the best single reference for your Jeep.
http://thejeep.com/shop/TECH+MANUAL...75+Jeep+Technical+Service+Manual+Reprint.html

Turner's is not the only place to get this, but it's the easiest to link to. I advise that you get the manual and read it. No one source is perfect, and it won't answer all your questions and solve all your problems. However, it will give you the background information about these mechanical issues that it seems you are missing.

 

check the ignition module on the steering column. I had the same problem and replaced everything only to find out it was the ignition connection and it cleared up when it was cleaned thoroughly. Cheap to replace too. Mine was on my 360 but the the 258 has the same set up. It is a 3 inch long two piece on the out side of the steering column about half way down the shaft.

 

thanks for all the help guys I haven't been able to check into anything on the jeep. Its not at my house right now as the garage is taken up with another project, and I have guards all this week so I won't get to it until at least next week.

been repainting my other truck in the garage sorry its not a jeep but I like both.