Carb sync using Twinmax ?

[buster73]

Anyone ever tried to use an electronic "Twinmax" FI/Carburetor balancer to adjust Weber carbs. I own one to sync the FI of my motorcycle and it works so well that I thought using it to fine-tune my Weber carbs. Was wondering if anyone out there has already done this ?

[304065]

Does it require a vaccum port at the base of each carb? That's the real issue vs. a STE type synchrometer. You would need to position the vacuum tubes precisely in some kind of adapter for the velocity stack to get the identical reading without affecting the engine's performance. Ditto those who have fabricated their own "carb sticks" out of a yardstick and a length of clear tubing and some food coloring/water.

Further, there is a differential pressure transducer available for a few bucks that will generate a voltage with regard to the difference in atmospheric pressure it sees across its two ports. If one were to hook a regulated voltage to this and then connect suitable pipes to vacuum ports to a pair of cylinders with a check valve to hold the pressure you could generate a result that could be datalogged. (same thing as a MAP sensor really)

The sporto had vac ports on the base of the throttle bodies. You would have to bore the manual shift version. Maybe there's a vacuum signal from the 72-73 plastic MFI coldstart ports?

[buster73]

Originally posted by john_cramer
Does it require a vacuum port at the base of each carb? That's the real issue vs. a STE type synchrometer.

Thanks John. A vacuum port on each carb would certainly be the best solution (that's how it works on my bike). I already checked and found that it is possible to stick the 2 rubber vacuum tubes down right into the narrowest part of the Weber venturis and they seem to be positioned quite well and should not disturb the air flow too much. If this is not good enough it should be no problem to manufacture a simple jig that would position the tubes inside velocity stacks or venturis at a defined depth. I guess ' just give it a try and report about the outcome.

The Twinmax is basically an electronic differential pressure transducer that compares the pressure between two ports. The good thing is that the sensitivity is adjustable so it can be used from a very rough setting down to an extreme fine tuning.

[buster73]

Tried to use the Twinmax today. Works great when using the two vacuum ports on each bank to syncronize right bank and left bank. Unfortunately it does not work with the tubes inserted into the velocity stacks to sync each cylinder individually. Guess they must be positioned behind (resp. below) the butterflies to pull enough vacuum. Next time I have the inlet manifold out, I might drill some additional ports for each cylinder.

[Early_S_Man]

Guenter,

How about using the old injector ports that have been plugged?

[buster73]

Originally posted by Early_S_Man
Guenter,

How about using the old injector ports that have been plugged?

Thanks, great idea. Might work. Have to take out one plug to check.