Slant Six Forum :: Questions on Carter BBD main jets and venturi screws

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Questions on Carter BBD main jets and venturi screws https://www.slantsix.org/forum/viewtopic.php?t=39784	Page 1 of 1

Author:	Fab64 [ Sat Apr 10, 2010 2:14 pm ]
Post subject:	Questions on Carter BBD main jets and venturi screws
Hi all, I hope the Carburetor Experts can answer a couple more questions for me. To re-cap, I have two Carter BBD 2-bbl carburetors. Hopefully, one of them will be going back onto my 225 Slant (originally a 1-bbl, stock rebuild, I've made no other mods as far as cam, compression, etc.): 1.) I believe is off a 318, year unknown 2.) a real "Super Six" carb (has the bent PCV fitting), model 8087S, from a late 70's Aspen/Volare Carb 1 runs very well, both cold and hot, but gets terrible gas mileage (11-12 city, maybe 17 highway). I've tried running with Carb 2, but can't get it to idle consistently once it warms up. Therefore, my plan is to swap main jets (and maybe venturi screws?) from Carb 2, into Carb 1. My objective is to run well, and improve my abysmal gas mileage. Q1: is this a feasible plan, or will internal differences in the two carbs cause other problems? I've removed main jets from both carbs: Carb 1 jet 1: 120-389 jet 2: too chewed up to read number Carb 2 jet 1: 120-386 jet 2: 120-388 Q2: Shouldn't both jets be the same size? Venturi Screws Carb 1: 570 Carb 2: 569 Q3: Would there be any mpg advantage to swapping these screws, or would it cause problems? The arrow points to the "intake check ball" (the ball bearing underneath the plunger): This was missing in Carb 1. Presumably, the purpose of this is to keep fuel from entering the hole beneath the plunger, as the plunger goes down? It must be there for a reason, so. . . Q4: What might happen if this ball is not in place? As always, thanks very much for your help. Roger

Author:	olafla [ Sat Apr 10, 2010 4:03 pm ]
Post subject:
Hi fab64. What happens if the ball is not in place: nothing! You'll just push the fuel back, the ball's job is to shut off the possibility for the fuel to run back to where it came from! Pushing 'the pedal to the metal' only makes a 'clonck!'. The fuel that is in that chamber, is the volume of fuel intended to spray into the airstream in your carb when pressing the accellerator pedal, if it is not there, you will experience the worst bog ever. The BB in Carter BBD also stands for ball and ball, and they're there for a reason. The 8087S is found on page 44 in manual 1 below, '77 Aspen/Volare supersix, same as my carb! See the carb FAQ at the beginning of the engine section, for jet numbers and metering rod sizes, see this link, you may find the answers to some of the questions you have there. Olaf

Author:	olafla [ Sat Apr 10, 2010 4:27 pm ]
Post subject:
Just another comment; as for the sizes of the venturi screws you refer to, as well as the venturi inserts they are screwed into, jets, metering rods and anything that normally should translate to a size in inches, millimeters, square nostril hairs or whatever; forget it! If anyone can come up with a single clue; hurrah! I haven't found any references anywhere to numbers vs. sizes. Olaf.

Author:	Fab64 [ Sat Apr 10, 2010 6:47 pm ]
Post subject:
Thanks for the response, Olaf. Now I'm having another problem, and I'm not sure what is wrong. Before putting Carb 1 on my car in January 2009, I re-built it. At that time, I didn't find an intake check ball, so I put it back together without one. It ran great, and didn't have any problems (other than poor gas mileage) for about a year. I then switched to Carb 2 about two months ago, and haven't been able to get it to run right. Today, I swapped the main jets and venturi screws from Carb 2 to Carb 1, and also put the intake check ball from Carb 2 into Carb 1. It started and ran very smoothly, but would bog down whenever I tried to accelerate. I removed the venturi screws, and re-installed the originals. No change. Then I wondered if it might be the check ball I installed. I finally located the repair kit instructions, and they say: "Check balls must be installed in their proper locations. Failure to do so will cause hard starting and/or inability to accelerate". This seemed contradictory since, as I said, mine never had one in the first place. So I took it back out. No change. I tried pumping the accelerator while looking down the throat, and I can see that very little fuel is coming out. So it looks like a problem with the accelerator pump circuit(?). I removed the Venturi screws and the entire Venturi assembly, and inspected all the holes. I put it back together and re-adjusted the metering rod and step-up piston. No change. About the only thing I haven't tried is swapping out the main jets, and re-installing my originals (although I don't know why this would cause the problem). I know the metering rods go into the main jets, but I didn't think the fit was that tight. Plus, when the accelerator plunger goes down, the metering rods are lifted up from the jets (which would make them fit more loosely). Is it possible the rods are too large for these jets? Other than that, I'm wondering if it's possible some air or fuel passage has become gummed up or clogged while the carburetor has been sitting for the past two months? Tomorrow, I'll try swapping the main jets back. If that doesn't do anything, I'll probably disassemble the carb, and try blowing out all the passages with compressed air. I've given up for today, and am open to suggestions. Thanks. Roger

Author:	jimmy the C [ Sat Apr 10, 2010 11:25 pm ]
Post subject:	BBD Jets
Fab64 in my inexperance mine did the same thing, what i had to do was do a wet float ajustment so the fuel level just spilled over into the pump well, That gave me a good squirt, Then when setting up the rod ajustment, with the throttle closed, set the sliderlock screw for the lift rod half way in the slot, (RICHER) Dont go to far or the rod will come out of the jets and hang up at wide open throttle, They tell me this is wrong yet it worked, also the bowl cover was a little warped so the fuel wasnt sealing for a true pressured fuel flow, whew knew,so i filed down where the screws hold the cover down (just a little) Used a new gasket and it fixed my problem. Try the jet thing you can allways change it back, Also i found that if the throttle blades have the little hole in them, it makes the engine idle to fast so i found some that had no hole or half moon carved out for the EGR port and fixed the idle, the blades had a 303 stamped on them, good luck brother

Author:	66aCUDA [ Sun Apr 11, 2010 6:05 am ]
Post subject:
On my BBD I soldered the holes in the butterflys. Which cured the idle problem. Frank

Author:	olafla [ Sun Apr 11, 2010 3:11 pm ]
Post subject:
I have to correct myself, the parts list I referred to actually have the sizes for the jets as well (BBDs and TQs). Sorry Olaf.

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