Anyone use a synchrometer to help tune dual quads?

[cleandan]

Hello all.
I am wondering if anyone has ever used a Synchrometer (STE-SK or other) to help tune dual quad carbs? In this case BJ and BK carbs.
I am thinking, with an adaptor to cover the whole carb inlet, or just the primary inlets, this might be a good way to get both carbs in synch at idle.
Any thoughts.

Thanks and have a great, but 6 foot seperated, day.

[Drew Pojedinec]

You could....
But how does this account for discrepancies in the intake distribution?
How does this account for progressive linkage?
If using IR intake I would think it’s essential.
If using a dual plane with a plenum I dunno, seems like I would just give the engine what it wants/needs to run well.

That said, if you have one, why not play with it and see where it takes you?

[Falcon67]

Tell you what I do - I set both throttles to "zero", link the carbs and use the front carb to set curb idle.  I don't use progressive linkage so it may be different for progressive.  Also, you can set both carbs to show just barely a square of the transition slot or a little less.  You could then tweak curb idle by turning both the idle speed screws the same amount.

For mix, I connect a vacuum gauge to the manifold vacuum port on each carb, one at a time.  I then set the idle mix for just a little fat from best vacuum.  Re-set curb idle turning both carb idle screw the same amount, then connect the throttle linkage such that it doesn't change either carb's curb idle setting and has as little play in the link between the carbs as possible.

[pbf777]

Hello all.
I am wondering if anyone has ever used a Synchrometer (STE-SK or other) to help tune dual quad carbs?
I am thinking, with an adaptor to cover the whole carb inlet, or just the primary inlets, this might be a good way to get both carbs in synch at idle.
Any thoughts.

Thanks and have a great, but 6 foot seperated, day.

     Yes!  But you''ll quickly realize that in most instances the fact that the carburetors are sitting on a common plenum is a saving grace as inequalities in flow sums, for many reasons, thru each venturi at different positions will generally vary greatly.  If intended setup is for one to one throttle function the single cover adapter over each individual carburetor as a hole will aid greatly in ones' understanding of the lacking in the execution of the throttle linkage.   
   
     But also, assuming all other variables within the carburetors are equal is to seat each set of throttles, noting the R.P.M. drop, and equalize, though the primaries vs. secondaries may prove be different for proper idle and off-idle transitional operation.       

     Scott.

[cjshaker]

Yes!  But you''ll quickly realize that in most instances the fact that the carburetors are sitting on a common plenum is a saving grace as inequalities in flow sums, for many reasons, thru each venturi at different positions will generally vary greatly.  If intended setup is for one to one throttle function the single cover adapter over each individual carburetor as a hole will aid greatly in ones' understanding of the lacking in the execution of the throttle linkage.   
   
     But also, assuming all other variables within the carburetors are equal is to seat each set of throttles, noting the R.P.M. drop, and equalize, though the primaries vs. secondaries may prove be different for proper idle and off-idle transitional operation.       

     Scott.

  I didn't understand a word of that...lol  But I do know that, unless you're running a tunnel ram, sheetmetal or tunnelwedge intake, the carbs are not on a common plenum.

I don't know how others do it, but I just tinker with adjusting both carbs until I'm satisfied with the idle. I don't like using just one carb for idle because you're basically starving 4+ cylinders and causing them to run hotter. I just keep lowering each primary until I'm happy that both are doing their share of the work, typically where a 1/4+ turn in will almost stall the engine. That keeps both primaries from being too far open, exposing the transfer slot.

[yellercat]

How bout' three carbs? Offering this on the chance that some of the theory may be usable or adaptable to the FE. (of which I am a rank amateur)
On the six cylinder, with three separate intakes, and three side draft carbs; I always, always, always set the air flow prior to 'adjusting' the mixtures. FWIW But the straight 6 is a whole different beast from intake to exhaust flow.

[BattlestarGalactic]

After dynoing my 462 a few years ago we watched the fuel each carb used.  With all the blueprinting we did we never got both to be equal.  We took it as intake design(Dove tunnelwedge).

I've been curious about using a synchrometer on dual carbs(seen them for single bike carbs).  Even with three vehicles with dual quads I've never really needed anything fancier then a screwdriver.

Just last year, my '69 F100 was having carb issues.  Erratic idle, hard restarting, etc.  I had tweaked on the carbs(1850's) over the years but I finally pulled them, balanced all the shafts/blades.  Got them set back on, did some very fine tuning over both carbs and it now starts easier, idles better cold, doesn't diesel, etc.  Seems over the last few years of tweaking I got them so far out of whack they just couldn't work well together.  Now it is a whole new animal(back to normal).

[Stangman]

Normal whats that

[BattlestarGalactic]

Uh, well..       ....good point!!!!

[mike7570]

My dual quad tuning - Make sure throttles open all the way and together. Jet for best mph. Adjust idle so it won't die in the pits. That's all 

[Drew Pojedinec]

I dunno about other folks, but I find with progressive linkage it is best to cover all transfer slots, just barely barely. Set idle with secondaries but so NOT expose secondary slot.
If more idle speed is needed, only use primary carb. Not because it effects idle negatively, but at cruise with one carb cracked and the other closed, the exposure from the secondary carb t slot can pull a lot of fuel at that high vac/ low throttle input.

Obviously not important at all for a racer, but very nice for a street driver.

[cleandan]

Drew, about how far open are the secondaries when using them to set idle?
Say from just closed, 1/8 turn, 1/4 turn, 1/2 turn...? (too bad that screw is hard to access)
This dual quad setup is in an ERA Cobra, 427, BJ/BK carbs, that sees primarily street cruising and show gathering use. I am setting this up for the owner and he states he will probably never race the car.
I suspect his hot road adventures will consist of fun onramp bursts, and maybe a stoplight run here and there, otherwise it will be simple driving around.

Currently things work and run pretty well but I just want to try and get them spot on for road use if I can.

[Drew Pojedinec]

Depends on the engine obviously.

I toss the flat head adjuster and install 8-32 brass set screws 1/2 inch long.
Put a drop of purple loctite in them so they stay in place.
This way you can adjust them while the carbs are installed with an allen wrench.
Later carbs take a 10-32

Closed throttle on 2x4’s is a big part of the battle. Exposed t slots lead to rich idles, and often complaints of the same nature.

[funsummer]

In reply to the first post, i can see no benefit in balancing idle with to much accuracy.
1, its common plenum so naturally cylinders will balance from that.
2. You mentioned idle, nothing exciting happens at idle, so no point been to fussy with it.

Have balanced few triple SU carbs on in line 6 engines, using vacume tool, balance idle vac, but more importantly balance the carbs with the throttle cable adjusted tight as the long shaft tends to get a bit of twist so use vac to balance the individual butterfly's.
Also own a nasty motorbike that has 6 carbs running onto individual cylinder intakes, have a 6 Vac gauge cluster for that one, its time consuming and very difficult to access.
i would say most people are more concerned with balancing throttles when linkage is loaded up or wide open to assure max HP.

[cleandan]

Thanks for the reply funsummer, but your post seems to assume a lot concerning the use of this particular engine and car. WOT is important in many respects but when the car in question will spend basically no time there it becomes the lesser worry.
This car, eventhough it has a very nice dual quad 427, will spend a LOT of time at idle, or just off idle.
With that in mind, if I can achieve the best idle, and transition, I think all the other aspects will fall into place pretty good.
The ultimate in HP is not important here, nor is the quickest ET or highest MPH...All that is just extra that will never be realized because of how this car will get used.