Technical AFR gauge with ZOOMIES

Best way I can think of is to build a set of sacrificial zoomies. Match your real design, but in plane I coated steel. Put a bung in each one so you can move the sensor to each cylinder.

 

An A/F gauge is not all that important at this point, you can see the exhaust pipes and know it's rich. It's been pointed out with this type of exhaust, an O2s isn't going to read right anyway. Fresh air is drawn in that will throw off the readings.
O2s are ment to be about 30" from the valve with pipe down stream to keep fresh air from hitting the sensor. Also, O2s do not need to be grounded, so it's easy to wire one to a metal rod and shove it up the pipe for a quick read.

Jetting shouldn't effect idle, and not knowing the carburetors, I can assume like 99% of others, idle does not go through main jets. FLOAT level can effect idle.

Raise the timing if needed.

Set idle speed with the linkage unhooked to all three carburetors, a Unysinc synchronizer would help with this just to confirm all three are working equally. If you don't have one, back each idle screw out till the throttle blades are closed counting the turns, then using a .001" or .002" feeler gauge, set the idle screw till the feeler gauge is a snug fit to the throttle lever, you will need to hold back on the throttle lever slightly. Remove the feeler gauge and count the turns to open the throttles, just pick a number or use the amount you turned to back them off. ALL three must be equal. A dial indicator can also be used to find the starting point.

Start with all six mixture screws at 1.5 turns out and fire up the engine, get it up to thermostat temp.
Now tweet the mixture screws, IF YOU TURN ONE, TURN ALL SIX THE SAME AMOUNT. Very small increments will be needed. A vacuum gauge will help.
Keep slowly leaning it out with all six screws. You want highest vacuum reading with the smoothest idle. Richen back up if it stumbles or bucks.

Keep the idle rpm where you want it by adjust all three screws equally.

700 rpm and 13" of vacuum are reasonable numbers, so you should be able to solve this.

Just remember, you have one big carburetor divided into three parts, so treat it as one unit with 3 set points and 6 metering screws. Use micro adjustments.

If you get the idle straightened out, consider getting rid of the progressive linkage, it will likely run a lot better. 250 cfm is not really enough for a semi-radical 355 cu in engine. This kinda explains why it will clean up the plugs after just a short drive, it's to lean.

 

Can you elaborate on this a little please? I'm not too old to learn something new. How does timing/ignition effect richness at idle? Thanks.

 

Thanks Joe, will do as you say for a starting point.

 

Normally when you advance timing it will raise your idle-which means you close throttle plates more down.

 

I would think if all cylinders are rich, then there's a good chance you can use and AFR gauge on any exhaust on your zoomies and begin trying to make timing, or carb adjustments until that one cylinder cleans up. Likely the others will also clean up since they all seem to have the same rich exhaust.

 

Increasing the timing raises the cylinder pressure because you are starting the burn process sooner.

 

Blue T 1983 BBC


Black T here Blown Mopar

 

Thanks guys, but this isn't helping explain a rich condition. Maybe I'm just thick headed (my wife would agree... ) Yes, advancing the timing will raise the idle speed, which you them correct by backing off the idle adjustment, which closes the throttle plates, as you said, but how does that result in a rich condition. The reduced air flow past the throttle plates will reduce the fuel being drawn through the idle circuit, right? And adjusting the air mixture screws should correct any rich condition, no? What am I missing?

And increased cylinder pressure, how is that affecting the air/fuel mix?

Thanks guys.

 

Increased cylinder pressure, lighting the mixture sooner will create more heat. The hotter the motor the more complete combustion you will have. The more complete combustion the cleaner your exhaust will be. But looking at those pipes that thing has never got close to getting good and hot and even with the above items addressed it probably still needs the carbs leaned out. It really just depends on if you want function above form ? Pretty sure your not dealing with much more than 3 or 4 hundred hp here, so how much fuel does it need. Those screens over the carbs could very well be causing some reversion there also. I assume there is not filter choking it down ?

 

Joe, just came in,
1. unhooked linkage
2. backed off all 3 idle screws
3. made all 6 a/f screws 1 turn out
4. plugged dist advance
5. warmed up and set timing to 24deg-vacuum went up to 14-14.5"
6. tried adjusting a/f screws to vacuum and I have it now at 1 turn on main and 1/2 turn on secondaries, seems to be idling good, if you turn screws out 1/2 turn more it runs like poop and black smoke out pipes, I even tried acc rods on summer setting (no change)
7. seems to idle good, plugs kinda black, but nothing on pipes, need to drive it but it's to cold here.
**** what about running with just main and 1 secondary hooked up that starts opening at about 1800rpm's. Idle at 750..

 

doing everything with no scoops or filters on it, Thanks

 

With my exhaust system off the car and 18” header extensions my AFR readings at idle are off the map, the gauge will not register anywhere close. Now at wide open throttle I do get correct readings and the gauge is very responsive to jet changes. My O2 sensor is located in the collector about 8” upstream from the reducer flange.

 

Thanks, I really only care about idle and up to 3-3500 rpm (cruising).

 

@Larry Kirwan , also if not aware
Most modern gas off the pump will show more blacker in color different then Older gas formulas of the past Unless race gas / Fuel ,
Also smelling Rich , vs Really Rich..
( look @ tail pipes on modern DD EFI)
My self when sitting the butterflies ,
I use like paper clip , .020 round just to get @ first all the same gap,"Base line"
Bore & edge of butterfly.
On all carbs , then adjust as needed ,
Air & Idle ,

just some other ways if not yet know for balancing,

 

Thanks, I alway's buy non-ethanol (who knows what I get?) I"m at point of needing to drive and check a plug.

 

You cannot use those multiple vacuum gauge tools on an intake with a common plenum, vacuum will always be the same at each point on the intake. Those are for motorcycles or other engines with individual runner intakes.

 

miss post what & How I would use,
Not below carb with individual separate runner, On top to balance carb's , Drawing the same , in stead of purchasing
2,3,4 -8 Uni Syc 's
My self have 4 , that I calibrated all to read the same,
I have both styles I feel the plastic one works better.
I thinking out side , & I have used my hand held data logger,4 sensors compatible also for weird situations

 

Definitely not that..

 

Do not consider the outer carbs as secondaries, they are not if it is idling off them as well as the center. You need to readjust all three to the same setting.
Keep it in your mind, this is 750 cfm carburetor split in three pieces.
It serves no purpose to have one idle richer than the others if all three have the same throttle opening.
To be true secondaries, close off the throttles totally and block the mixture ports.