Vacuum Gauges and setting up Carbs

The lumpy idle should go away with a carb sync.

Another item that can cause a lumpy idle would be a vacuum leak at the intake boots, or in the clean air system.

T.

Hi Toddh. On bench setting the butterfly, reading the manual i was of the opinion they should be closed at throttle close. What size wire are you using using as a closed gap? Or have i read the manual wrong?

Now that I've got your attention: ( Perfectly balanced ! ):woohoo:
First thing that needs qualifying is understanding the calibration nomenclature of the sync-gauges used.
The manual uses cm/Hg.
These "sticks" are calibrated in cm/Hg

If you're using something more common like these gauges, Note they are calibrated in "Inches/HG"

A problem (and confusion) can arise (for the uninitiated) if you're using "Inches/Hg" (8"/Hg is good !)
but trying to achieve a cm/Hg (higher #) reading.
8" Hg = 20.32 cm" Hg
1" Hg = 2.54 centimeters Hg
Bench Sync.: Cut a strip of paper 6"L X 1/2"W and fold it in half - 6" X 1/4" with a tight fold. I've added the fold since doing a similar suggestion previously. Place it under a butterfly plate and adjust the linkage so the paper can be pulled out - with some drag. Do this by "Feel" for the three carbs. You're now within a decent range to do the vacuum sync. I don't advocate using anything Metal be it "wire" or otherwise. "Feeler Blades" will not work. Too wide and too stiff.
1/8 of a turn on an adjuster [strike]will[/strike] can give a significant change in reading.
You can do a search in this forum for previous discussions re: Carb sync., bench sync and regarding rough idle when everything has been set up correctly "Pilot jets" (idle jets)
Adjusting the sync-screws too much causes binding.
Bouncing "needles" or "sticks" can be dampened by stuffing some cotton into the intake manifold adapters.
I use MIG welding tips (wire size irrelevant) as manifold vacuum adapters. Drilled-out the threaded end and packed cotton into it to dampen the pulses.


A simple extension for the center carb. A screw-driver handle drilled out and epoxied to the extension.