i'm not sure why the stock carbed engines are run individual runner style.

on a high overlap engine, it is better, as the pulses are best kept separate. something like a PP has lots of exhaust gas dilution at low speeds, there is a fuel cloud over the carb sometimes, etc etc.

and on the later EFI engines they use the pulses to give a supercharging effect. something you can't really do with a carb, just due to the manifold design. they can get the reversion of the closing of one rotor, to help cram more fuel into the other.

but on a stock engine with a carb, i dunno why they run I.R. style, actually some years have balance ports but still, no plenum

 

Some carbs like a constant signal at the booster venturi, not the spikes and peaks. Has to do with the internal fuel delivery in the emulsion tube system. Shorter height is usually more responsive and will like a ram system.

Tube size for a balance tube only needs to be about 3/8".

gd

 

Are there any drawbacks/side affects to using the balance tube?

 

http://www.tjwakeman.net/TR/Net_intakeCrossoverTube.htm

 

Piston engine design aside, I would think so. The balance tube damps out the spikes and smoothes out the pulses. Depending on the size and length, you might have to adjust the mixture and or idle jet. You could effectively tune with this. A large tube with variable limiter in the middle.
I used to use this for tuning Class 10 1.6L engines to determine exactly the plenum size that worked best.
At the end of the log runner/trough, I would weld a 1" pipe nipple and attach various lengths of capped PVC pipe to determine where in the curve we needed the help of plenum tuning. Then would make teh volume meassurement to add that to the plenum.

gd

 

Strong vacuum signals mean better fuel control.

The 12A I had that got 30+mpg? Nikki carb with a "reworked" intake manifold...

 

yep! the nikki is quite good, our friend bengina, has my old SA22, and it'll get 22-25mpg no problem, and its just stock. add header/free flow exhaust and it should only get better

oh and like yours, the SA gets best mpg in the 3500-4000rpm range.

 

Yup. Strong steady signal. Spikes and valleys in vacuum signal deter from proper metering. EFI smoothes these signals electrically. They can't respond fast enough or even out the delivery. Early GM systems used to deliver rich lean signals to the injectors. So the mean was stoichiometric at 14.7.

gd