In setting the idle mixture screws for the twin 4-barrel carbs on my blower set up, do you do it like a single carb set up and work back and forth among the 4 screws to find the highest vacuum? I had heard once that you set the idle only using the front carb, but I don't know how much sense that makes.

Also.. I run 36 degrees of total timing, but I want to increase the initial timing to 18 dgrees but maintaining the 36 degrees total. Do I do this by changing to the larger black advance stop bushing in my MSD distributor (black = 18 degrees mechanical advance), so that when I set it for 36 degrees total, that would mean that I must now have 18 degrees initial?

thanks

As far as the idle goes, you can adjust/set it with either carb, once the linkage is hooked up if you increase on carb idle it will move the other one the sam amount. Use the front or rear, doesn't make a difference. The front one is just easier to get to (when you have two carbs mounted sideways).

The short answer is, Yes. You adjust them just like a single carb. You only have 4 screws to deal with on your set-up. Just jump back and forth until you have the idle speed and throttle response you want.

I set my air/idle mixture screws by idle RPM with the blower. I move around and adjust all 8 screws. They should be open about the same amount (primaries about the same and secondaries about the same on each carb) meaning if I have the front carb set with the screw 1 1/2 turns out n the primary side, I make sure on that same carb the other screw on the primary side is ~ 1 1/2 out as well. I start with all of them 1 turn out, fire up the car and start adjusting, you can hear when you hit the sweet spot. On Holleys I adjust the idle screws to give me the proper amount of tranfer slot showing (primary blades) I then will use the secondary side to give me more idle speed if needed. I know you run Edlebrocks, but I wanted to add this stuff just in case someone does a search for this same thing down the road.

You might want to PM Eric on theMSD timing. I know he runs and MSD and is very knowledgable. I run a Mallory magnetic distributor, the timing curve is adjusted by using "keys". I don't know how the MSD's work.

One thing I learned tuning 4 weber carbs.
As you open the throttle, the carbs come off their idle screw stops, the linkage then controls the position of the throttle blades, it is very difficult to get the play in the linkage evened out to pick them up equally. It may not matter as much with a blower and two carbs since they feed a common plenum, but if you have a way of putting the idle speed screw on the linkage, then the weight of the carbs is allways pulling on the linkage leaving no way for the carbs to get out of sync as they are opened.

If you do that, then the carbs should be balanced to equalize air flow by adjusting the linkage at idle. A unisyn is used to measure air flow thru each carb and balance them. If you had a cross-ram like the old Weiand or Mickey Thompson type, each carb feeds the other side, and there is no vaccum connection between the carbs so even flow is critical to good running/idling.

Also.. I run 36 degrees of total timing, but I want to increase the initial timing to 18 dgrees but maintaining the 36 degrees total. Do I do this by changing to the larger black advance stop bushing in my MSD distributor (black = 18 degrees mechanical advance), so that when I set it for 36 degrees total, that would mean that I must now have 18 degrees initial?

thanks

Yep, use the black bushing. Set your timing with the vac hose disconnected by reving the motor until the mark stops moving. Set your total timing for 36* and let the initial timing fall where it may -- it will be close to 18* (I think mine is a little more than that with the black bushing, no biggie). The more advance at idle the better as far as I'm concerned, especially with big cams.

David, with the blower set up, the syncronization is not a problem. I ran dual carbs back when I used to play with VW's (air cooled) and you are right about getting them syc'd if you didn't they sure ran bad. Dual Webers

The way the blower linkage is set-up there is no play or anything. Once you set the linkage and carb, they can't get out of sync.