Stalling diagnosis

[marc]

Friends, my 84 J10 with the original BBD carb has taken to stalling as it slows down to a stop sign or is stopped. I gather this indicates clogged idle jet tubes (i've bored them out) but it is inconsistent. As it occurs once or twice a day, I am wondering if it could be something hanging up in the carb, maybe the stepper motor? It occurs after the truck warms up. I will likely pull the tubes and clean them then re-tune the carb. Had the carb rebuilt a while ago but, when I bought it, it looked beat up. When the guy who rebuilt it pulled the stepper motor out, it fell apart. Someone had glued the parts of a broken motor together and the glue had failed. I happened to have a carb I bought off of Craigslist as a source for parts and a bench top study and had him use that stepper motor. Slightly different model number, carb for a manual transmission rather than automatic. Wouldn't clogged idle tubes cause a consistent stall?

[tgreese]

I would do two things.

First I would inspect the idle tubes for dripping, as described here. http://www.jeeptech.com/engine/carter.html Likely I would drill out the idle tubes, regardless of findings.

Second, I would bypass the idle stepper motor and ECM. I would expect the condition of the stepper motor won't matter if it does not need to step. This bypass converts the variable idle jet under the control of the stepper motor to a fixed idle jet, as I understand it.

http://web.archive.org/web/202002240818 ... gnition99/

If you search for "Nutter bypass" you will find quite a few dead links. This mod is not as topical as it used to be, as these vehicles get older. I expect the subject vehicles are gone or their owners have moved on to other solutions besides the BBD. You can find many of the missing older web pages using the Internet Archive (Wayback) as above.

hth!

[Srdayflyer]

check the carb butterfly shaft/s, 2/4 bbl? mine were worn and fluttered causing constant issues at idle i had the carb overhauled at a carb shop they foung the shaft stepped and the shaft bore oblonged, when i reinstalled it it rand good but the 360 was just a cold bear to get going, so i went F.I. instead ,something you may want to check to eliminate a problem i ran across with mine, especially if its the oem original carb

[tgreese]

The Carter BBD is a conventional 2-barrel (2 venturi, 2V) carburetor, ie not a progressive design. From '83 on, they came with an electronically controlled idle jet (the stepper motor) which helped to meet emissions standards at the time.

If you had the carb professionally rebuilt, the shop should have checked the throttle shaft for tightness. It is true that the carb body (in any carburetor) wears out around the shaft and this leaks air (a "vacuum leak"). This air leak will change the idle depending on how the linkage comes to rest against the idle stop screw. Move the shaft up and down / side to side in the carb body and the idle will change. You can also test for vacuum leaks by backing the idle speed screw all the way out. The motor should slow and stop.

A loose throttle shaft can be repaired, either by fitting a slightly larger shaft or by bushing the carb body. A common procedure for a professional shop.

The BBD is well know for idle problems. The two fixes I suggest above were popular for these carburetors, but the BBD always seemed to be the carburetor that everyone loves to hate. Lots of aftermarket solutions if you don't have an emissions check where you live. The only two emissions-legal solutions that I know of are the original BBD carburetor and all its associated devices, or the Howell EFI kit which is CARB-certified and legal in 50 states.