Zenith Mod

TinCup

TinCup

Well-known member
Working on a Canadian built 31 roadster and when pulling the Zenith 2 carb apart I noticed these mods. Seems to me like I have seen it before but I can't recall where. Is this a modern replacement?
 

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That is a "pressure balanced" carb. The original bowl vent has been plugged and a new path has been machined into the body and venturi to vent the bowl out to the air inlet.

This allows you to run an air filter and not have it make the carb run rich if the filter is a bit restrictive.

HTH.
 
I don't think it was done correctly. The air vent passage should go from the float chamber to after the air cleaner, but before the choke.
 
That is exactly how mine looks and was done my a man who's name on eBay is tazzmann if I remember correctly. After years of abuse it still runs great, not as good and when i got it from him but still fantastic. Best carb I've ever run on my pick up
 
Smog Tech has it right! (between filter and choke). As said, purpose is to balance out restriction caused by added filter!
 
James G. said:
Smog Tech has it right! (between filter and choke). As said, purpose is to balance out restriction caused by added filter!
Click to expand...

I have one also ... if I understand Smogtech's post?

If you open the choke and look inside at top of the throat, the port is behind the choke plate... that is if you close the choke; the port is behind the plate and not visible.

When I tested it briefly, I noticed that you can close the choke with engine idling and the engine does not stall out.
 
Renner's Corner pressure balances carbs (and flows jets) altho I don't know if their modification is like this one.
 
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Just Talked with Dave Renner and this is how he Pressure Balances the carbs he builds
I Explained to him what i was thinking on how I wanted to do this and, he agreed it is basically the same

Tinkirk/Terry
 
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