I have this edelbrock 6x2 setup on my model a, solid linkage, power valves deleted and 53 jets. The issue I'm having is when I punch the gas down sometimes I get a back fire out of a carb and a puff of black smoke out of the headers, once that's out of the way if I stay in the gas she runs strong. Any ideas on what to do or check would be greatly appreciated
I would PM HAMBer Littleman, He has run SBC 6 x 2 intakes on his A. Here's a sample posting: https://www.jalopyjournal.com/forum...an-excellent-94-carb-new-parts-source.256802/
That's what I'm trying to figure out, it started off where the plugs were completely black, now there a brownish cold with a little black, when I blocked the power valves I put bigger jets in, and it wouldn't run for nothin, took those jets out and put 53s back in and it ran better but still back fire, it back fires when I'm getting out of the idel circuit, if I tap the gas quick then punch it down the car takes right off now issues, it's when I'm cruising along and or come to a stop and lightly get in the gas, then it back fires
You're a braver man than I am, Gunga Din. I've never, ever had a 6x2 that didn't have a flat spot, a stumble, a bog somewhere in the rev range. Your backfire out the carb is as likely to be ignition as fuel. When was the last time you replaced plugs, wires, cap and rotor? Bottom line - lookin' cool costs. jack vines
The vacuum advance doesn’t change anything at full throttle . What’s the base timing ? Any more details on the engine ?
I've only known 2 men that have run a 6X2 setup on hot rods, both only used the middle carb on each bank, other 4 were for show and they do look Kool. 6 X 2 without progressive linkage is a race deal IMO and you are probably over carbed for your mild street use engine, again IMO. Lots of variables to play with/adjust to hit the right combination, Good Luck. I never cared much for multiple carb setups, back in my day, had Tri-Carbs, easy to tune, used progressive linkage, various 2X4 deals, never the right combo, and my junk always was faster/better/consistent with one 4 barrel, correct size and tuned for what I had. The multiple setups are mostly for show, again IMO. Check your manifold vacuum, could be the source of backfire problem.
It sounds like maybe it is getting too much pump shot, with the puff of black smoke. I would slow down the accelerator pump shot, or switch to a progressive linkage. I use a progressive linkage on my 8 carb Hemi, with the center 4 opening about 1/2 way before the outer 4 even start. Also, I have no idle circuits on the outer 4. It runs great on the street and drag strip.
I'd ditch the straight linkage and pick up a progressive.. i run all 6 on my 324 olds with 97's has no issue runs on 2 until i really get on it. Also should try a new set of plugs maybe a hotter plug and a timing adjustment should do the trick. Not sure what a stock jet is for a 94 but i went with stock jets, and power valve in the 97's and have had zero issues as my daily driver.
It's a process. The accelerator pump arm has three holes that control the pump. Start with all set at the inboard hole to get less shot. If you then need more, start by adjusting the center two carbs. I would consider running power valves in the two center cards. Make sure that the power valves and block off plugs are machined for 94s. New Holley PVs don't fit tight and will drip by the threads. You might also bump up the jets in the center two carbs by two sizes. I usually start with the linkage off, close the end carbs idle screws and back off the idle speed screws on the end carbs. I try to get idle speed and mixture on the center two carbs and then balance with the end carbs if needed. An AFR gauge will be your friend. Then hook the linkage up without disturbing the carbs throttle arm positions. Drive. Adjust. Repeat. Maybe many times. The biggest issue is getting enough air velocity through the carbs so that they will meter correctly. Depending on your intake design you might need carb spacers. Sometimes they help. And a cam with decent idle vac numbers.
Put power valves back in it. If you are running straight linkage the carbs need to function as original. You might need ones that actuate at a lower number but it will run properly with them.
Added fuel enrichment under conditions of low manifold vac tuned by the vac rating of the power valve. If you are going to be playing with a 6x2 you will need to have a good understanding of carb function as that setup is not a bolt on set it and forget it kind of thing. That's why so many are running around dummied up.
I would remove the vacuum advance and try running straight timing and see what that does.. If it cleans it up try working from there.. Maybe more initial with less advance or just run straight timing. I've done that on street engines for hundreds of thousands of miles... When I get into carbs plural, the vacuum advance is usually the first thing to go..
Stock 94 jets are 51. Putting power valves back in an engine that has a backfire condition is making more work for you. 2X^ double check those power valve block offs, sounds like one may be leaking vacuum causing the backfire. I would change to 50's or 51's and reset the accelerator linkage 2X^. Plus use only two carbs for idle. The other 4 should have the idle screws bottomed out AND the throttle plates adjusted to be fully closed at idle. BUT only make one change at a time...just like on a race car. Small plenum, long ports you can use a lot of carb......big plenum and short ports for racing, use very tiny carbs on the street, 450's or 390's 2x4 or original Holley / Ford 94's. Your mechanical advance needs to be in by 2500 rpm. The vacuum advance is an option if the mechanical is working right.
it will be easier to tune with more initial timing. crank it up to 30 at idle and try that. if it helps go back ant limit mechanical timing in the distributor.
I run 6x2 straight linkage on my car. 12 initial and 32 all in by 2,500. Mechanical advance. All carbs function as original. Progressive linkage is designed to be used with primary and secondary carburetors ie no idle circuits. Turning in idle screws is not the same as not having an idle circuit. There is nothing easy about running six carbs direct on the street but it can be done and run properly without belching smoke and stumbling.
Initial acceleration with opening all 6 carbs at once is a delicate balancing act. I would suggest you get a uni-sync tool and make sure each carb is p***ing the same amount of air at idle so they are synchronized. That should be your starting point. Motorcycle mechanics synchronize multiple carbs all the time. A friend, and motorcycle guy, cured a poor accelerating Astin Martin by using his uni-sync tool and setting all the webers the same. Flat spots went away.
Would I be better off replacing this distributor with a mechanical advance and get rid of the vac? I'm gonna be putting .50 jets in for starters, I wonder if closing the outer 4 carbs idle circuits off will lean those cylinders out? Thanks alot guys!
Vac. canbe locked up.,if you have distributor that also has mec. advan. built in. If it has no mec advan.,you need one that dose. Vac. adv. with 3 or more carb.s is not a working thing for the most part.
I put size 50 jets in, along with a new coil and distributor. One of my issues might be the vac advance I drilled into the carb, see the pics below, I'm getting fuel in the vac line which might be causing some of my issues?? When I took the car for a spin a little bit ago, I was getting into the throttle and a puff of smoke? was coming out of the carb, it would run decent up until I pushed the gas down, it hesitates and puffs out of the carb
I am not saying if you should, or should not, be using the vac advance. I personally don't. But if you do, you can decide if you want manifold vac or ported vac off the carb. The vac port on the carb is the br*** plug above and to the right of where you drilled the carb. It's 3/8-24 straight thread.
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