Quad carb setup information help
Rat, a few more questions. When you say 22 are you referring to my timing? if you are referring to timing, isnt that a lot? Ive never run anything that far advanced so will i run into cranking/starting hard when hot? And what type of machine are you referring to?
I've ordered my pin set and drill set along with a few pin vices. A question I have is once I start playing with the circuits do I do one carb at a time or do both carbs at the same time.
Anything else I need to do before starting this?
This will be a long process. I hope you are around until the end. Lol
Thanks Rod
Yes, I’m talking about 22 initial timing. You can maybe squeeze some more out of it if it needs it. At 14 you just don’t have enough initial timing.
In order to get 22-24 initial and still keep the total where you want it, you have to shorten up the mechanical advance.
Looking at your 14/34 numbers tells us you have 10 degrees mechanical advance in the distributor (which is 20 on the crank) and you have 14 initial. If you want to get to 22 initial you only need 6 degrees of mechanical advance in the distributor.
The math is 6 degrees in the distributor, which you double for timing at the crank for 12 degrees of mechanical advance. To get to your 34 degrees of total advance you’ll need 22 initial timing.
That will lean up the idle a bunch. What distributor do you have?
I do both carbs at the same time. So get your bleeds and T slot restrictors done on both carbs at the same time. Any changes you make you do the same to th carbs.
Make sure you don’t have one carb “leading” the other. The best was to do it is with a Unisyn. Edelbrock makes it and it’s part number 4025. Then you need a 4150 carb cover. It can be plastic or aluminum. You drill a hole in the middle of that cover and glue the unisyn to it. Once you do that, you can get the carbs “sync’d” up.
The unisyn is just a simple manometer. What I do is get the timing set and everything else as close as I can and get up to operating temp. Then I disconnect the front carb because it’s easier to get to.
Then stick the unisyn on the back carb and see what the unisyn says. It’s adjustable so I make the meter read in the middle. Once I see where that back carb is, I put the unisyn on the front carb and take a reading. No matter how close you might think you are with your initial idle settings with the idle screws, you won’t be real close and one carb will be leading (flowing more air at the same idle speed) as the other.
If you have that, you’ll get all kinds of weird issues, like tip in stumbles that you can’t tune out and all kinds of things.
Once you see the difference between the 2 carbs you use the idle screws to make both carbs flow the same air. It doesn’t matter if one carb is open a bit further than the other as long as both flow the same amount of air.
You might be a bit surprised of how things like firing order, carb placement on the plenum, header length, runner length and shape and such can affect how much each carb needs to flow. And that’s the end goal. Getting both carbs to FLOW the same at idle. You can’t (or you shouldn’t) just close the throttles to zero and then say open each carb 1.5 turns and then adjust it from there with equal turns on each screw. Both carbs may be open the same but they may not be flowing the same, and probably are not. That’s why the unisyn is so important.
