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Carter BBD on 273ci

bsellers89

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Hello, all. I rebuilt the Carter BBD on my '66 Belvedere II and it runs much better. Even though the accelerator pump squirt is still weak on one side, the car is noticeably peppier and snappier in response. This is a fantastic carburetor on this engine!

I'm very curious what these two holes leading into the carb throat are. Sure looks like 2 vacuum leaks to me ... should these be plugged?

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Idle mixture bleeds?
 
Leave them alone! Needed for proper fuel distribution...
 
Hello, all. I rebuilt the Carter BBD on my '66 Belvedere II and it runs much better. Even though the accelerator pump squirt is still weak on one side, the car is noticeably peppier and snappier in response. This is a fantastic carburetor on this engine!

I'm very curious what these two holes leading into the carb throat are. Sure looks like 2 vacuum leaks to me ... should these be plugged?

View attachment 908828 View attachment 908829

IMO...
These holes are Fuel vapor vents that were provided for possible relief of percolation issues. I'd just leave them ss you found them. FYI....there were 2 seperate models of Carter BBD (which stands for Ball and Ball Dual). The first was denoted 1 1/4" seties (which is what you have and is used on small block LA engines) and the 1 1/2" series which is used on the B series engines, 361s & 383s. You are correct they are OUTSTANDING in operation give decent fuel mileage, good performance, and are easy to understand and rebuild. They were generally used thru mid 70s when Carter went out of business and Mopar switched to Holley. Just my opinion of course.
BOB RENTON
 
Very cool, grateful for the info. Re: fuel percolation issues - what is the symptom of that were these holes not to be there?

My rule for "excessive vacuum leak" is if the idle mix screws cannot go so rich as to bog the engine. On this BBD, they can be adjusted "too rich," so the amount of vacuum leak caused by these holes is not a concern.

Correct, mine is the 1 1/4" carb. Big fan!
 
Very cool, grateful for the info. Re: fuel percolation issues - what is the symptom of that were these holes not to be there?

My rule for "excessive vacuum leak" is if the idle mix screws cannot go so rich as to bog the engine. On this BBD, they can be adjusted "too rich," so the amount of vacuum leak caused by these holes is not a concern.

Correct, mine is the 1 1/4" carb. Big fan!

I believe, starting with the 1968 model year, more vehicle/engine combinations were using Mopar's CAP (Cleaner Air Package) and later CAS (Cleaner Air Systems) to control vehicle emissions of HC (Hydro Carbon) and CO (Carbon Monoxide).
For the smaller Carter BBD series, like yours, the idle mixture screws were pinned to keep them from being turned out too far. The mixture needles had a machined area on the threads and after setting them during manufacture, they were pinned to limit their travel. Perhaps, someone modified the carb to eliminate this feature or replaced the throttle body with one that was modified. Fuel mixtures were leaner as well. In addition, spark advance characteristics were modified to slowdown the rate of advance using lower initial advance but more total mechanical advance and sometimes adding a vacuum control valve on cars with standard transmissions and higher temp thermostats. All these changes resulted in hotter operating temperatures and during a hot soak restart condition, fuel percolation or boiling can occur, resulting in higher emissions, hence the need for additional vent passages to reduce this over rich condition. Today, this condition is exacerbated, by the Ethanol blended fuels that boil easier due to their lower vapor pressure index. Just thought you might like to know.....
BOB RENTON
 
I have not been able to re-establish a strong squirt either on my BBD model rebuilds.
Its POSSIBLE that the accelerator pump inlet check ball, at the bottom of pump well is not seating, allowing a percentage of the accelerator pump's volume to be waisted, rather than thru pump discharge channel, outlet check valve and nozzles. Most of the time the rebuild kit furnishes these check valve balls. It is a usual practice, with the aid of drift pin, to lightly tap the old check ball, forming a new seat for the new check ball. It may be possible that the accelerator pump's plunger (either leather or neoprene) may be leaking or the well itself is damaged or scored. Is the actuating linkage set correctly, providing the correct pump stroke? Are you using the correct outlet check valve? Just thinking out loud.....
BOB RENTON
 
Very good points all around. Good idea to tap that check ball to aid seating it. I'll be back in that BBD again one day to try and remedy the weaker driver's side accelerator pump squirt. For now, the arm has been moved on the throttle linkage to deliver a larger squirt. A hack fix, but remedied the low RPM stumble. The engine is also whooped - leaks 75-80% compression past the rings. New plugs installed this week; borescope showed mirror finish on the cylinder walls. 15w40 & oz. Bardahl's stop leak keep the 273 purring well enough! Usually get 17mpg summertime. HEI distributor on the motor currently.

Thanks again for the history on the engineering of these Mopars. I love learning where they came from and the thoughts behind how it was done.
 
You're welcome....
The "little" 273 engine is a great power plant....well designed and in the 235 HP version is an excellent performer. Years ago, i "built" 1967 Plymouyh Belevedre II with a first generation LA 318, with 273/235 HP parts (cam, lifters, rocker arms, modified intake manifold), recurved distributor, A727A trans and 3:55 rear gear, snd a thermal drive fan clutch and dual exhausts. The car came with the hd suspension and brakes. The combo ran extremely well....surprised a few Camero, Mustang and even a few Road Runners in stop light contests....wish I still had it!!!
BOB RENTON
 
Yo, that is a cool cruiser indeed! A 5spd from a Dakota might grace this '66 Belvedere II one day ... ahhh, those "one day" plans ...
 
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