I am designing a downdraft linkage for Webers on the E3s and E9s. It will be another month or so before production and I will announce availability as soon as I can. In the mean time, can someone tell me what the circled lever in this pic is for? It seems to activate some kind of switch I believe. Is it necessary?
Downdraft Linkage System question
- Thread starter halboyles
- Start date
It is for a vacuum operated diaphragm to slow throttle return when decelerating, controlled by the speed relay and a dashpot on the firewall. Most no longer work after 50 years.
and used to rev the car when tuning the carbs 
So, it sounds like it is unnecessary for most users.
Well, at least this vestigial part has some purpose!and used to rev the car when tuning the carbs
Most of these diaphragms are frozen and don’t move anyway
jmackro
Well-Known Member
Hal:
The arm & tab for the diaphragm probably isn't necessary. I have Webers on my car and removed that diaphragm many years ago; it works fine without it. Perhaps they were more critical with the original Zenith carburetors.
I have been monitoring you website from time to time, checking whether your improved linkage was available yet. Glad to hear that it is getting close.
The arm & tab for the diaphragm probably isn't necessary. I have Webers on my car and removed that diaphragm many years ago; it works fine without it. Perhaps they were more critical with the original Zenith carburetors.
I have been monitoring you website from time to time, checking whether your improved linkage was available yet. Glad to hear that it is getting close.
Jay, they were a rudimentary attempt at smog reduction.
jmackro
Well-Known Member
Yes, I can believe that. So you're saying that neither the Zeniths nor Webers rely on the diaphragm for functional reasons, just an attempt to slightly reduce emissions. I doubt that many e9's are currently subject to emissions tests - none would be in our home state - so eliminating that lever & tab shouldn't trouble many of Hal's prospective customers.
Last edited:
I think (old recollections from my CA smog license days) the diaphragms or "dashpots" were used to reduce NOx emissions by slowing down the deceleration of the engine, enabling a more complete burn of the cylinder charge as the engine RPM came down during stop and go driving.
Here in PA, 1974 and earlier are emissions exempt, in California it is 1975, so emissions requirements may still exist for some states.
Here in PA, 1974 and earlier are emissions exempt, in California it is 1975, so emissions requirements may still exist for some states.
Thank you.. We hope to have them available by the end of this month. I'll make an announcement on the board.
jmackro
Well-Known Member
OK, terrific. Will you recommend a specific thickness of carb-to-manifold insulator, or will the linkage work with a variety of insulator dimensions? I ask because the stock linkage will go over-center when used with Weber carburetors and too thin (or was it too thick?) insulators.