Holly/Zenith carb
 

We have a couple of Holly carbs that neither have the secondary well in them. The hole in the body is not threaded and is to small in diameter to install one. Does the Holly not use the secondary well or are we missing something?

Re: Holly/Zenith carb
 

According to Steve Pargeter's Zenith model A Carb Restoration Guidelines. Holley manufactured Zenith type carbs Jan - Jun 1928 had no secondary well- cast well only no insert. Holley Jul 1928 onwards incorporated a secondary well. Steve P also states Zenith Model A carb had no secondary well from 1927 - Junn 28. Steve Pargeter's booklet is a mine of c Model A carb history; I treat is as the definitive history .
PS you are likely to find on these early carbs that the cap jet is in centre line rather than offset like the later ones, also likely to be originally double venturi ( though I find a single venturi works just as well)

Re: Holly/Zenith carb
 

That is what we have then, haven't seen one before. We will see if we can get one working. Thanks :)

Re: Holly/Zenith carb
 

All the jets are the same and the idle is only shorter on the later ones because of the base of the secondary well. The shorter idle jet can be used in either carb. ( I don't think the original longer idle jets are available nowadays anyway. )

Re: Holly/Zenith carb
 

The Double Venturi carb used a idle jet #10 , a cap jet with the orifice at the bottom of the jet and a #10 compensating jet. As previously stated the main and cap jets are in line rather then off set like the later carbs.

The double venture is available from A&L Parts if you want one ?


They are a good running carb when properly rebuilt.

Ron

Re: Holly/Zenith carb
 

A typo? Surely the compensating jet should ideally be 18 or thereabouts. (drill size 64-65 flow rate thus approx 138 ml/min)

Re: Holly/Zenith carb
 

The double venturi is available from many A parts suppliers. You will notice a different sound, kind of / almost a low whistle , hard to explain when you are at a slow idle and you are right near the carb. Well restored ones sell for quite a bit more than standard zenith cards.

Re: Holly/Zenith carb
 

I looked for a few years for a double venturi carb and couldn't find one. A few years ago I was at a large Model A parts sale and bought a carb with a stuck throttle from a guy. Neither of use realized it was a double venturi until I got it home and got the throttle unstuck, or I wouldn't have got it for $25. Some days are better than others.:D

I haven't finsihed rebuilding it yet to try it out though.

Re: Holly/Zenith carb
 

John,

You are correct, made a typo error. The compensating jet is a # 18 and is .036 opening.

Also, the most difficult items to find for the Zenith is the forged Throttle & Choke levers.

Ron