Erratic carb operation.

Not enough info. Year? Engine size? Market spec (US, California, Canada)? "Older" could be anything from the 1930s on up to 1988, the last year of carbureted Dodge pickups in North America, depending on your definition of "old". "V8" could be anything from a 277 "Whale" Hemi to a 318 to a 360. "2 barrel carb" could be a small Carter BBD, a large Carter BBD, a small Stromberg WW3, a large Stromberg WW3, or any of several Holley models.

Choke system is in need of repair and/or adjustment. Includes the choke thermostat, the choke pulloff, all associated linkage, and (if a post-'73 model) the choke thermostat heater and choke thermostat heater control box and associated wiring.

Too vague to diagnose. Need conditions. Hot engine or cold? Every time? Sometimes? When wet out? When dry out? When cold out? When hot out?

Accelerator pump system is in need of cleaning and reconditioning.

Sounds like you have several issues. When's the last time the carburetor was disassembled, thoroughly cleaned, and rebuilt?

DS

Mid 80's. It's not my truck. I'll have to ask next time I'm visiting.

Canada.

OK, we'll look into that.

Hot.

Unfortunately no. Also, when running rough, will sometimes settle down of accelerated sharply at highway speeds.

It's always dry here (desert)

Doesn't seem to matter.

We were thinking of changing the linkage adjustment to see how that affects it.

He just got the truck a few months ago and for now it's his only wheels. When we get his car mobile that carb will damn sure get removed, cleaned and adjusted, but I was hoping for an interim fix.

Thanks for your advice

Sounds like a choke pull off problem for the cold running symptoms. Of course, if it's leaking vacuum there that affects running all the time too.

Step One is to get a FACTORY service manual for the truck. They're not difficult or expensive to get, and will save you a LOT of grief compared to any other source of info (Haynes, Chiltons, the Xeroxed sheet that comes with a carb kit, etc). The carburetor and choke system, especially on an '80s emission controlled vehicle, will really only work correctly if everything is built and set exactly the way it's supposed to be. Unless you've got a lot of experience with this specific carburetor on this specific kind of truck, don't touch it until you have the book, which will pay for itself many times over.

And of course, don't remove or disassemble the truck until you have a carburetor rebuild kit and plenty of good quality carburetor cleaner on hand.

Note that your random rough running could be caused by non-carburetor components, such as the EGR valve.

Well, before changing anything, remove the air cleaner lid, and with the engine hot and shut off, briskly snap the throttle open while you peer down into the carburetor (with a flashlight if necessary). You should see two *strong* shots of liquid gasoline squirted into the carb throat each time you operate the throttle. If not, the accelerator pump isn't working right.

DS

Very, VERY good advice. I'll add one other subsystem to check: heated air inlet malfunctioning and letting in cold air when it should be sending in warm air. I had this fail on a 1986 carbureted Mustang guaranteed carburetor icing in humid or cool weather. I also had it fail in a 1989 DeVille, causing overheated air to enter the throttle body (symptom: engine knock) and a 1986 Le Baron (2.5 liters TBI engine

-- same symptoms as the DeVille). It's an easy check with a vacuum pump and gauge.

The inlet may also have something Ford used to call a "cold weather modulator" (don't know whether Chrysler used this) and, possibly, a check valve in the vacuum line feeding the heated air inlet. If these components are present, they, too, have to be checked. I'd start with the thermostatic element, simply because in the three cases I personally experienced this was the part that failed.

Hope this helps,

Bohdan

Daniel J. Stern wrote: