Transition ports question - Zenith carbs

[Einar Irgens]

Dear Pelican forum.

I expected that at idle all of the four transition ports would be hidden by the butterfly (watched from underneath). I have problems obtaining this for the first barrel on both my carburetors. Even though the screw does not touch the throttle plate (the half moon shaped thing):



the first hole is visible:



As far as I can figure out, the angle of the first butterfly can not be adjusted in relation to the throttle plate, as it is slid onto a square part of the shaft and locked in place.

So, should I adjust the other butterflies to match the first one? Probaly better than having two different positions.

Einar

[Einar Irgens]

No opinions on this?

[1QuickS]

It is a routine procedure to file the edges of the butterfly valves so they will be exposing the first transition port simultaneously. Use a small file (I use a file that is similar to a points file), open butterflies and take a small cut with the file at an angle that is as parallel to the butterfly as you can make. Check to see results and continue until all three butterflies have same relative first progression hole alignment.

I found the Zeniths to partially expose the first progression hole at idle which is has the butterflies more open than fully closed. Same is true for Weber IDTP carbs, IDA Webers have first progression hole higher up so that at idle the butterfly blocks the first hole. I think the Zeniths and IDTPs were designed that way due to emissions era requirements.