SU's just won't balance!!

[Da Flash]

I just recently rebuilt a pair of SU's using the ZTherapy kit and tape (a little pricey but, I learned alot). The rebuild went fine except that now I can't seem to balance the carbs at higher (2000-3000) rpms. They both have the same vacuum reading at idle (about 4-5 on the scale, I'm using syncrometer not a Unisyn) but once I raise the rpms the front carb pegs the meter (30) while the rear carb is still pulling the same amout of air/ vacuum as it does at idle. I've played around with the mixture nuts and, the idle screws (now I know why they only work at idle) but this hasn't changed the balance. I know that there's a screw that is on the linkage near the front carb that supposed to effect balancing but it doesn't have any effect either. I've also checked for leaks with carb cleaner, that doesn't seem to be an issue.

Other than that the carbs are working good, well as good as unbalanced carbs can.

[Victor Laury]

The center screw on the "dogbone" center linkage, is the throttle-on balance adjustment.

Go back a step

Loosen the center linkage screw completely, which will separate the carbs at idle and rebalance at idle. then, raise the rpm to abou 1800 or so using the screw on the balance tube. then balance the carbs again using the center screw on the center linkage.

If you had tried to idle balance the carbs without loosening the center linkage screw, you'll get a false balance that goes to heck with the throttle on.

[Da Flash]

The center screw on the "dogbone" center linkage, is the throttle-on balance adjustment.

Ok I think here lies the problem, I'm not sure which screw you're talking about. I see 3 screws connected to the linkage

1. the screw that's on the balance tube (I pretty sure this is the fast idle screw)

2. One screw on the center linkage just to the right of the front carb (attaches to the dashpot)

3. One screw on the center linkage just to the left of the rear carb.

Not quite sure if the bar that goes between the 2 carbs with balls on the ends is the "dogbone" but thanks for your imput!!

[Victor Laury]

1. the screw that's on the balance tube (I pretty sure this is the fast idle screw)

Right. It's really there only to help set the throttle-on balance by raising the rpm's

2. One screw on the center linkage just to the right of the front carb (attaches to the dashpot)

Mine is missing, so is the dashpot. This is to adjust the dashpot idle speed. I think you should do your intial balance adjustments with this loose as well.

3. One screw on the center linkage just to the left of the rear carb.

Yes! this one ties the two carbs together. Loosen complely for idle balance and speed adjustments and adjust for throttle-on balance adjustments.

[Da Flash]

Thanks Victor, that did the trick for balancing the carbs. I still can't get the mixture correct on the rear carb, the front carb is fine, when I push the piston pin up the engine hesitates a little then runs slightly worse than if I let the piston drop. (the spark plugs for cylinders 1-3 are tan to slightly gray) The rear is a different story, if I lift the piston with the pin the engine will sputter and die pretty quickly!(spark plugs are dry and black) From what I've read this indicates a lean condition but, even if I screw down the mixture nut all the way (4-4 1/2 turn, this should be as rich as the mixture nut can get it) I still get the same result. I've recheck the float level, it's the same as the front and measures about 14mm. So I checked for leaks with carb cleaner, no leaks. This weekend I'd like to get a ColorTune to check the mixture better. Now I have a few more questions;

1. Do I need the dashpot for anything, I de-smogged the car last year?

2. I thought that "dry and black" indicated too rich, not too lean?

3. Any suggestions on how to remedy my mixture problem?

Thanks Bro', LA huh? I'm down in the OC, do you come down for the West Coast Nationals?

[Victor Laury]

Check your float levels. remove the front bowl cover and turn it upside down. Measure the distance from the cover to the top of the float. Then duplicate that measurment on the rear cover and adjust the rear to match the front.

>Thanks Bro', LA huh? I'm down in the OC, do you come down for the West Coast Nationals?

I love taking over the City of Orange one day a year and Hell yes I'll be in Long Beach of the National Convention!!!

[Da Flash]

I got sick of playing around with the mixture nuts on my carbs so I went out and bought a ColorTune, MAN did that make getting the mixture down simple. After all was said and done my SU's get better milage and less exhaust fumes!

I think the problem that I was having is that when you lift the piston on the front carb and listen to the exhaust, you make the adjustments to the BACK carb. No wonder when I would change the mixture on the front carb and lift the piston for the front carb, I wouldn't notice any difference!!