Balance Tube?

Balance tubes were popular with the old Zenith carbs (Similar to Kadrons) on early Porsches and VW engine conversions.  Mostly, the balance tubes were used to provide an adequate vacuum signal for the vacuum distributors that everyone used at that time (the 1950’s and 1960’s) because centrifugal-advance distributors had not yet become popular.   If you were to use the dual-throat carbs and intake manifolds that we have today with a vacuum advance distributor and simply connected the disti vacuum signal to any one of those 4 intake manifold runners, the vacuum signal would pulse (spike) once every other crank revolution.  The disti would go nuts, pulsing all over the place and never give a good spark signal.  The engine would never see adequate spark advance to run properly.

The cure is to connect all of the intake manifold runners together to smooth out the vacuum signal (balance) to provide a smoother spark advance signal.  Some older disti set-ups (and a lot of racers, because they run at wide open throttle more often) plumb a vacuum buffer tank into that system.  That is just a small sealed can connected to the vacuum line to provide a vacuum reservoir to the system to smooth out the vacuum signal at the distributor as well as slow its’ action.  

All that said, some single-throat dual carb setups like to be connected together at the intake manifolds because the carbs are single-throat and benefit from the vacuum effects of merging the intake ports and the better merging of the fuel/air mix.  Think of this as not pulsing the carbs by starting/stopping the air/fuel mix for one cylinder, but providing a more balanced intake flow being drawn by all four cylinders and both carbs.  It makes the whole system a bit more efficient, but that only works on single-throat carbs.  If you are running carbs like dual-throat Webers or Dellortos and/or are running a centrifugal advance distributor, you will probably not see a benefit to installing manifold balance tubes.

I hope this is not confusing.  If so, ask questions and I’ll try to clarify.

Nicely put, Stan!  Love it.

So, Danny....

In order to answer the second part of your query (do we recommend this), we would need to know what you currently have for carburetors (brand and model).  

While it sounds like an easy process to “just add balance tubes”, it may not be, nor may it be necessary.  

Tell us what you’ve got for carbs and let us make a recommendation.

Newbie Danny Nipomo Ca. ('18 VS Az) posted:

Hello everyone,

I was recently recommended to add a "balance tube" (not sure on the terminology) connecting the duel carburetors together....

What is the advantage of this and do you recommend I do it? Anyone's opinion would be great...Again I am a newbie here so layman's terms would be appreciated..

I got tired of tuning so I put in two gas pedals. One for each carb.

OK, Danny.....

Since those are Kadrons they are single-throat and your mechanic is correct.  They would probably benefit from a balance tube between the intake manifolds.  He probably believes (rightfully so) that the balance tube will help with the idle, but it should improve mid-range performance, too.  Sounds like you’ve found a good mechanic!  

You may luck out and have manifolds that already have the bosses in them to attach balance tubes to.  That would make them easy to upgrade.  If not.... sells a balance tube upgrade kit for dual-port engines;

They have a similar kit for a single-port engines, too.

Talk it over with your mechanic and decide which direction is best.  Sounds like he’s done this before.

Yup, late to the party but a vacuum balance tube smooths out dual single throat running on our beloved pancake motors. 1/8" pipe thread nipple into each manifold and connect with 1/4" ID rubber hose or a metal tube with rubber hoses on each end. I've seen people install solid metal lines from one manifold to the other for this and also for fuel(carb to carb). NOT a good idea, the engine expands about 1/4" and then contracts when cooling. Cracks WILL happen in solid metal lines, so always put rubber at either end.

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