Need new air bypass control screw for my carb

fizeus · fizeus's Garage

Hi all,
I'm looking (and googling) for a new set of air bypass control screws for the Zenith 40 TIN.

While it seems mixture control screws are still available, air bypass control screws seems unavailable.

Also my local official PO dealer told me they are out and cannot be ordered.

Can anyone suggest where to buy them ?

They should be screws marked by "C" in the attached image.

Thanks in advance

Jack Stands · Jack Stands's Garage

I'd try to call Paul Abbot at Performance Oriented (530-899-8371). He does carb rebuilding, and has been working on Zenith conversions, so he may be able to help.

dvdt · 09-14-2014, 02:19 PM

I am rebuilding my Zenith 40 TINs. They are from my 71 911T 2.2. I noticed that the air bypass screws (same as in above post) look as if they had a through hole drilled through the threads normal to the screw direction, which has been plugged. Is there supposed to be a hole in these screws or am I just seeing things here. Thanks

fizeus · fizeus's Garage

Hi,
when I rebuilt mine I also noticed that the six air bypass screws have a hole in. It's normal. The hole seems closed with little metallic pieces. Do not remove the metallic material in the holes. I think it's a security mechanism to prevent accidental unscrewing caused by engine vibrations.

Also my carb has one screw with a free hole, anyway it works very good.
Do not worry about the hole (taped or free) because the air bypass mechanism works thanks to the top of the screw (on the top of the screw you'll see an undrilled part).

Hope this helps

dvdt · 09-16-2014, 05:47 PM

Thanks much for the reply. That definitely helps and I can go ahead and finish putting things back together.

chris_seven · 01-12-2015, 07:27 AM

I have only just noticed this post.

The 'hole' in the side of the Air Screws on the 40TIN carb should hold a nylon plug.

With age these plugs loosen and fall out which can be a problem.

The nylon plugs are an anti-vibration feature and are designed to prevent the screws from moving when the engine is running and causing an imbalance.

If you fully tighten the screw they will stay in place but you will lose the adjustment feature.

The Weber IDA Air Screw looks similar but the taper is quite different and it doesn't seal correctly.

I am just about to make some slightly longer screws so that they can be used with a lock nut in the same manner as the IDA.