brass plug insert with drilled hole above the mixture screw to limit fuel flow (throttle body restrictor viewtopic.php?f=19&t=63938 BBD idle circuit

The diameter of the barrels for this china clone carb and various real BBD carbs I have are all 1 7/16 inch - not 1.25" or 1.5". So explain to me why I come across references to 1.25 and 1.5 inch BBD? What are they measuring? I don't get that. Sae 1 1/4 designation , measured bbd and stromberg is right center of shaft to edge of gasket surface at the right spot. https://carbkitsource.com/tech/Stromber ... ergWW.html

air bleed early bbd with air bleeds below fuel level, fuel level too high too rich,too low too lean

Short vedio how it works start 6 minutes in https://www.youtube.com/watch?v=GQVunAA ... chEngineer

Solid fuel no air holes below fuel level, no air till very top of nozzle. Level of fuel in bowl has no effect on air fuel ratio only circuit timing, high fuel main system starts early low starts late.

Correct me if I'm wrong - The "solid fuel" term or idea comes from the venting of the accel pump well to allow vapor to be released leaving LIQUID (not solid) fuel in the well. If the carb has the boxy extension on the air horn -> does that make it the "solid fuel" type of BB . Box on un modifed carb means solid fuel for main system. Nothing to do with accel pump.

I don't remember details but I remember reading about the "solid fuel" thing somewhere pertaining to all but the earliest of the thermo quad which is also a Carter carbure.1971 first year thermo quad air bleed, 1972 and beyond solid fuel

- main venturi is smaller in super 6 (1 1/16 inch vs 1 3/16 inch for 318). I would have to take a few carbs apart to see where they're making this measurement. Slant six will run good with 1 3/16 venturi, bigger than that may be not. Idle and off idle will be fine, getting main circuit to start flowing ln time might be problem. Air flow will be slower less atomization and less vaporization. If might be good idea to check fuel level.

On these newer carbs with all the ports -

You've got an evaporative scavanging system with a port that comes off the boxy tophat airhorn extention that is supposed to go to a canister, I assume the other canister connection goes back the the carb to a port right beside the PCV port on the throttle plate housing. There's a valve inside the tophat that closes this canister line when you're off-idle.

So this means that at idle, there's a pretty good vacuum being applied to this tophat. Which means the air in the bowl section of the carb is exposed to a good vacuum at idle, way below atmospheric pressure.

If you don't have a canister, and you just plug the port on the throttle plate (leave the tophat port open) then is the carb designed for that? To have no vacuum in the tophat at idle? It may run and idle ok, but will it meter out the fuel as designed?

I don't know how much resistance to airflow there is normally in the canister. So it might, or might not, be ok to connect a line from the canister throttle port directly to the tophat port? Or would that flow too much air?

I've run many of these carbs with that line to the "top hat" simply disconnected, with no bad effects in how the engine ran.
There were different versions of the same carb, some had more vac nipples than others.
The BBD that I currently have on my /6 doesn't have the nipple on that "top hat" section. It was a "HD emissions" version meant for. a318. Back then "HD emissions"basically meant minimal smog control stuff.

Ok, can I get a reality check on these ports?



This is what I think:

1) to evap cannister source vacuum
2) choke diaphram
3) PCV valve
4) no idea
5) distributor advance
6) to evap cannister
7) no idea
Eight) no idea

Now maybe I'm mixing up 1 and 7, but still one of them is unknown (to me).
8 and 4 - one of those could be for EGR and the other for warm / heated air from air cleaner?

If I have a small port on the underside of the air cleaner housing, should I connected it to either 4 or 8 even if it's not heated air? In other words, should there be air flowing into either 4 or 8 for normal operation (instead of being plugged) ? I assume if one of them is for EGR and I don't have EGR then it should be plugged?

What is best port to run to a vacuum gauge?

-------------------------

Ok, crickets so far. Just to add a few more tid-bits about this carb:

I don't know what this indicates about the carb, probably shouldn't be able to do this, but I can dial the mixture screws all the way in and the engine will still idle, 500 rpm, vacuum 14 to 15. One turn out on both and rpm is 550 - 600, vacuum 17-18.

Got a real bad whistle when I first had this carb running with the supplied flange gasket (1/16"). Was coming from the throttle disks, only when I was dialing in the idle RPM I wanted. Very small change in RPM off-idle and the whistle was gone. I then got a new thicker gasket (3/8 or 5/16) like I had on the original BBD and I can sort of make the whisle come and go but this is much better now. I was thinking maybe I'd have to drill small holes on the throttle disks to stop the whistle.

I'll need to get a different choke thermostat rod, the existing setup is too short by about 1/2 inch, even with the correct thick flange gasket.

7 is for evap canister supply vacuum. That is copy of later bbd, 79 newest have to look at. 7 gets vacuum above curb idle at off idle speed , no vacuum at idle. Does not get full vacuum there is restrictor in carburetor, older units might be in canister. Not all canister the same, but all had flow restrictor some where.

2 looks right good place for vacuum gauge

3 looks right, 1and 3 go to same place? 1 might be power brakes

4 Heated air cleaner, just a guess, does not flow air just vacuum. 5 Dist vacuum advance