Diagnosing Carter 2bbl ('67 383)

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goldfish65

goldfish65

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My '67 Monaco...c-body of course but FABO has the best techs. Engine has a miss at idle and at low rpm's....for example cruising through a parking lot. Once the car is underway it runs nice, it has good acceleration, it starts up instantly and never stalls. I have checked/done the following and no improvement: new plugs, wires, cap and rotor, good vacuum readings, good compression in all cylinders. Carb was rebuilt very recently by previous owner. Today I saw that the accelerator pump is only squirting fuel to one side of the carb. Does that mean something else in the carb is not right? And what should I do? Thanks in advance!
 
Sounds like crud got in the float bowl.Worked into the accelerator pump/idle circuits.Idle circuit can effect to 2000,2500 rpm. Much more noticeable on heavier vehicles. Start with the idle circuit.You need to have compressed air for this.This is where you need one of those rubber tipped blow guns.Take a screwdriver,and a piece of paper.Turn the idle mixture screws,infill they seat.Count the turns,as you go.Write it down,do both sides.Take the air gun,blow out the threaded holes the screw came from.Reinstall the screws,to the settings you wrote down. Accelerator pump; you noticed one squirted not working.If possible,remove the squirter assembly,hit with carb cleaner,possibly force the residue out,with a welding tip cleaner. Just costs time,no cook.Good luck.Sorry about the novel.
 
I don't get how it can have a "miss at idle" and yet the "vacuum readings are good."

My strategy is usually a cursory look over at ignition, adjust carb idle, and see if you can get it to idle smooth, and see if both idle mixture screws have nearly equal effect

Then dig deeper, examine the dist. make sure the mechanical/ vacuum advance works, check carefully the cap rotor for dirt/ moisture/ carbon tracking, and check the wires for continuity. This could also be a fouled or even broken spark plug. Plugs CAN fail internally, but that's fairly rare

THEN DO a "backyard" cylinder balance test. You hear guys talking about "pulling plug wires." Don't do that. On breaker points ignition, the spark can cross fire when a plug wire is disconnected, and give you incorrect results, and with electronic ignitions, you can "kill" the ignition box

SO SHORT them to test. One way to do that is with a very thin probe, another is to get some very thin, small brads and pull up the dist. cap boots. Slip the brads down beside the plug wires in each tower, then start and warm the car.

take a grounded probe and watch your tach, listen carefully, and or watch the vacuum gauge. Short the cylinders one at a time. I do this at a dead slow idle, and again at about 1000--1200 RPM. Each cylinder should drop RPM/ vacuum and "sound" the same as each other cylinder. One that does not drop "as much" or not at all means that cylinder is not firing, and this could be from a number of reasons.

IF THAT checks out OK, one thing you can try before you remove the carb is to remove both idle screws, and squirt some pressurized carb cleaner through the holes. Then reinstall the screws and readjust the idle.

Your description of the pump squirt is telling. This is a simple nozzle in a "Y" which simply divides the pump shot pressure. So if one squirts and the other does not, you have gum/ dirt/ etc in the pump passages.

Frankly, if it's been awhile or "unknown" since the carb has been gone through, you should just order a kit, pull it off, and clean it out, then before you run it, flush some fuel out of the line by running the starter, hose in a clean container, and let it set. Look for dirt/ debri. Replace the fuel filter with a METAL filter, NOT plastic. Wix is a good solid brand, and NAPA filters are made by them. O'Really stores also carry Wix
 
Did not describe,fluctuation of the needle at idle on the vacuum gauge.Might be ,he doesn't know.Just a thought.....
 
The low speed miss/ rough idle is a common issue with BBD's. If your ignition system is in tune and working well, check the small brass down tubes in the center throat of the carb. You will have to CAREFULLY remove the choke plate to remove, clean and replace the nozzle assembly and clean the tubes.

A lot of jeep folks drill out the end to the next size so it becomes less suceptible to clogging. You can find a lot of information on the web regarding this issue by searching with Google for idle problems BBD carb.

Here's a nice example of the fix with pictures. http://www.instructables.com/id/Fix-idle-and-stalling-problems-on-a-jeep-cj-7-or-w/

You can clean out the accelerator discharge nozzle at the same time. I'd pull the top of the carb and see if there is a lot of dirt in the floatbowl too. Maybe change out your fuel filter while your at it.

FWIW: I had this same problem persist with the BBD on my slant 6 after this fix. It turned out to be worn distributor bushings. That problem resulted in identical symptoms to the clogged tubes.
 
Thank you very very much guys, this is what I was after.

Just to clarify, the carb was rebuilt a few hundred miles ago by the previous owner. The vacuum guage doesn't fluctuate at idle.
 
Just an update my brake booster is bad (I shoulda made SURE about this before) so when the new one gets here in a few days I will be doing the work myself, never done one, wish me luck. We'll see how the car runs then!
 
carter bbd?if so good luck.mine has the same issue after i rebuilt it.same thing after harms rebuilt it,so go figure.
 
Troubleshooting a Carter BBD:

Step 1: Raise hood
Step 2: Remove air cleaner and confirm you have a Carter BBD
Step 3: If you have a Carter BBD, it is the source of your problem
Step 4: Remove Carter BBD and install a 4 barrel intake and carb of your choice.

Problem solved!!! :thumbup:

Sorry to the Carter BBD lovers out there, but I've been through more than a few of them at this point, and after cleaning, rebuilds, more cleaning, tuning, etc, I have yet to be happy with how any of my cars ran with the 2 barrel, even with otherwise stock engines (usually 318's!). I've used Carter AFB's, Edelbrock's, Street Avengers etc, and have had very few issues with any of them, even used carbs that I just cleaned and installed. Not sure what is about those Carter 2 barrels, but they don't get along with me at all.
 
My friend told me they are prone to becoming warped (?) from people tightening the air cleaner wing nut too tight. Anyway one thing at a time, in a few days we'll see what difference a new brake booster makes. Thanks again everyone for your help.
 
I just unclogged a BBD, one shooter was dry and clogged. took about 5 minutes. Helped with the off idle stumble, but the 170 was in such bad shape (sorry R**) that it made no difference in power. Idles fine though!
 
...............I really dont think his 67 383 has a Carter BBD on it.........i cant remember the series # off hand.......u need to clean out the shooter.......r u running points , if so u may need new ones, is the vacuum advance hooked up at idle, whats ur base timing.....kim.......
 
Plug the brake booster vacuum line off David, you could be loosing vacuum there.
In the mean time check/remove your gas filter and see what you can get to fall out of the inlet side, if you see crud you need to remove the carb and bring it in the house and
unplug the shooter that is plugged up.. This would be a good time to update yourself on these BBD carb's , let me see if I have a carb brake down picture of a 66 model in my book..... I will share it here with you so you can see how easy it is to remove a shooter and even clean it up as it could need it.
 
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