258 w/Carter BBD running rough

[Grand_Wag_85]

I've got a high altitude Carter BBD on an AMC Eagle that started to act up 2 days ago. Main symptoms are stalling when stopped, rough idle and backfiring/popping thru the exhaust while coasting down hills. Normally it runs as if it had fuel injection and this is really out of character.

Thought I got bad gas so I put fresh gas in the tank, changed the filter, added the fuel system cleaner to the tank and cleaned up the inside of the carb with an entire can of spray carb cleaner. That did help a little but it's still idling rough.

Is this a common failure mode of the BBD? How can I get it to behave better? I'm gathering parts to do the 4.0 head swap and fuel injection so I'm trying to resurrect this carb instead of spending more money on the MC carb that will only see limited use.

[Stuka]

This is what I would consider "normal" for a BBD. A BBD that doesnt do this, is abnormal.

The issue is the idle jets plug up. So instead of just letting fuel atomize out, it drips. So you end up with these big drops of fuel, which results in a VERY rich running engine. I messed with mine for about 3-4 months after I bought my J10, got sick of it, and put on a weber. Anytime I cleaned out the idle jets they would work properly for a week or so. But then progressively get worse. The web is full of people complaining about this issue. I would consider the BBD to be the worst carb I have ever had to deal with. And that includes finicky multi-carb setups.

[Grand_Wag_85]

This is what I would consider "normal" for a BBD. A BBD that doesnt do this, is abnormal.

That's what I was afraid of. It's performed flawlessly going on 4 years now with awesome mileage too. I guess this run of luck had to end sooner or later. Gonna try and clean those Jets out and see what I end up with. I've got 2 or 3 other BBD's to cannibalize if need be, just gotta make it last until I get around to doing the fuel injection.

I've got a Weber on the J10 and it's done me right so far. Only issue I have is oil getting past the PCV valve and into the carb.

[carnuck]

Try this first: Cross #1 and #6 wires at the cap. Start it and quick rev a couple times to make it backfire. When the wires are put back it should run smooth. If not, then either the carb body is loose, the intake is loose or you have to go under the dash on the passenger's side and jumper the high altitude plug if you haven't already. I hooked mine up to a switch on the dash because I went up the pass so much.

[Grand_Wag_85]

Swapped one of my spare BBD's in and it runs a little bit better but still stalling...Now I know WHY that carb was taken off lol. Got another one without the stepper from the old J10 that I'll try.

Try this first: Cross #1 and #6 wires at the cap. Start it and quick rev a couple times to make it backfire. When the wires are put back it should run smooth. If not, then either the carb body is loose, the intake is loose or you have to go under the dash on the passenger's side and jumper the high altitude plug if you haven't already. I hooked mine up to a switch on the dash because I went up the pass so much.

I'll give that a shot. What's the purpose of crossing the wires, to get the backfire to clear something out?

I haven't done the high altitude jumper, never messed with it but I assume it's still hooked up the way it was when sold new. I'll check it.

[carnuck]

If it's not a high altitude car, the jumper won't be installed but it's usually still wrapped in the tape. Crossing the wires blows the crud out of the jets.

[Grand_Wag_85]

If it's not a high altitude car, the jumper won't be installed but it's usually still wrapped in the tape. Crossing the wires blows the crud out of the jets.

Yup it is a factory high altitude car. So on the non high altitude cars the jumper was included but not installed?

Didn't cross the wires but ended up taking the carb apart and removing the venturi assembly. Pulled the idle tubes, blew them out with brake cleaner, flossed them with 10LB test line, drilled them out with a 1/16" bit, blew them out again and put it all back together. The Eagle runs GREAT now and idles no problem.

Thanks for the help guys!

[Stuka]

Drilling the jets out will help prevent the issue from happening as easily in the future.