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useless carb balance tool

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Randy - since the butterflies in the DCOEs are permanently fixed to each other, could you explain why it's necessary to check both sides of each carb, rather than one side only? Why are the columns slightly different within each carb?

Enquiring minds want to know! :fat:

PS - with the manometer, you can easily check your balance without removing the air cleaners!! That's a strong feature right there!
 
I am a big fan of manometers. After fooling around for years trying to balance the throttle bodies on my 80's BMW M5 and Lotus, I started experimenting with manometer designs. I have been selling these to the BMW community for a while now. Full disclosure here is the link https://mantismanometers.bigcartel.com/

It is the only way to fully synch the throttle plates at idle or just off idle. It does nothing once the plates are open as the bypass ports are OBE. The reason you connect the tubes to all connected butterflies is to adjust the individual air bypass ports. You would be surprised how far off cars are from the factory.

The main benefit to the driver is the 80's ECUs stop hunting at idle and off idle parking lot conditions. Makes driving the car slowly and a very light throttle more enjoyable. Some of the 80's BMWs have enough power that you are just off idle at freeway speeds. Fine tuning the throttle bypass ports and setting the mechanical plates up correctly increases mileage and the enjoyment factor. Most tuners focus on max HP/Torque. Dynos runs start at 2K. I like to work in the ignored 1-2K range. I can't tell you how many times I heard "I just got tired of driving it..." Turns out the reason isn't that it isn't fast enough, it just runs terrible going slow.
 
steveg said:
Randy - since the butterflies in the DCOEs are permanently fixed to each other, could you explain why it's necessary to check both sides of each carb, rather than one side only? Why are the columns slightly different within each carb?

Enquiring minds want to know! :fat:

PS - with the manometer, you can easily check your balance without removing the air cleaners!! That's a strong feature right there!
Click to expand...
The different readings are because the exposure__the time the "shutter" captures the moment__is thousandths of a second frozen in time, and the cylinders are constantly "pulsing" at different times, depending on their intake stroke. To the naked eye, the readings are balanced (averaged, because we're__at least I'm not__fast enough to focus mid-pulse). ;)

While the pairs of throttle plates are fixed to the same shaft__two (2) venturis per carb__that's no guarantee that the airflow is the same. There is a compensation air adjustment on each barrel (2 per carb) and one side will always read higher/lower vacuum than the other when both compensation needles are completely closed. The side with the lowest reading is kept closed, while its mate is opened up to match it.

The following text and diagram was taken from the Weber's factory service manual; the example used is for two (2) carbs, but balancing three (3), four (4) or six (6) would follow the same procedure:

air_bypass_text.jpg


air_bypass_adjustment2a1.jpg


You'd be shocked at the number of people getting paid to "tune" Webers that have never heard of this, or think that those screws are for emissions, or some other such thing not applicable to "racing" carbs!

Once you have the individual carb barrels balanced, THEN you can balance and set the idle speed and tighten the linkages together, similar to how you'd do a pair or trio of SUs.
 
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