Carb Tune up tool

[Gary in NJ]

Can someone explain to me how an SU get's "choked down" by a UniSyn? The SU is a constant velocity design. Put any type of restriction before the carb body (whether a unisyn or a synchrometer) and the airchamber piston is going to adjust to the necessary height to maintain the proper airflow.

Obviously both tools work well. It might be helpful to the OP if we state WHY we prefer one over the other. Here, I'll go first:

I' damn-near 50 and I can't see for sh!t anymore. The Unisyn is easy to read.

That's about the entirety of the difference. Anything else is just nonsense. The two tools do the same dame thing but present the data in a different way.

[beermanpete]

I have a Uni-Syn. It definately changes the engine speed when used. It restricts air flow enough to generate a vacuum signal to raise the indicator bead. This restriction enrichens the mixture a bit.

The reason the suction piston does not correct for this is because the restriction is before the carb venturi and lowers the pressure in the venturi. This causes more fuel delivery. Even theough the suction piston falls a bit it does not offset the reduced pressure enough to maintain the same mixture ratio.

That being said, I don't think it matters. The balance will be set with the same conditions for both carbs so it should be balanced correctly. If I were to try to get it closer I would remove the balance tube and use mercury columns.

[LeonV]

I have a Uni-Syn. It definately changes the engine speed when used. It restricts air flow enough to generate a vacuum signal to raise the indicator bead. This restriction enrichens the mixture a bit.

The reason the suction piston does not correct for this is because the restriction is before the carb venturi and lowers the pressure in the venturi. This causes more fuel delivery. Even theough the suction piston falls a bit it does not offset the reduced pressure enough to maintain the same mixture ratio.

That being said, I don't think it matters. The balance will be set with the same conditions for both carbs so it should be balanced correctly. If I were to try to get it closer I would remove the balance tube and use mercury columns.

Exactly.

My problem with the Unisyn is that it has a big effect on flow into the carb, it's essentially a choke. If you follow the proper directions for using the Unisyn, they say to only keep it on the carb for as short as possible in order to get a good reading. This makes carb-to-carb measurements somewhat tricky and less precise as this method leads to inconsistencies. You also need to make adjustments to on the unisyn in order to get the ball reading in the correct range.

The flowmeter takes all the guesswork out of it, and leaves much less room for error. The Weber tool is very easy to read actually, easier than the unisyn. Plus, the graduations are clear and much finer which makes consistent measurements very simple, and there is no adjustment necessary in order to go from idle to high-speed balance. It also has a nice tapered rubber seal to place against the carb inlet.

Overall, it is a more accurate and user-friendly tool. The unisyn gets the job done but is more prone to error and a bigger pain to deal with. If I needed a tool to syncronize carbs, I'd get the Weber tool without a doubt, especially considering that they cost the same amount! Carburetor syncronizing is so much quicker and simpler with it.

Note that I've never said that a unisyn won't work, it's that the STE just works much better. Like I said, ask someone that's used both, or better yet, try the flowmeter yourself.