U20 SU throttle shaft reconditioning

[nismou20]

Thought I’d post this for some of you who are running with worn leaky SU throttle shafts and dont want to put down $350 for Ztherapy rebuilds. This is a budget refresh and by no means anything close to their’s. I like to tinker and since my U20 rebuild with thinned throttle shafts are running so well I thought I’d share my most recent attempt to reducing vacuum leaks.
Nissan took a cheap approach to the roadster U20 throttle shaft bushing by cutting a channel out of the shaft and using a piece a Teflon strip within the carb body ends. Due to the linkages on both ends and throttle springs constantly pulling down on both ends of the shaft the carb body ends and throttle shaft wears a elongated hole where vacuum leaks. I removed the shaft scribed a line with a copper plumbing pipe cutter just within the confines of carb body. Then took a very thin narrow triangle file and cut out a channel into the shaft on both ends. Bought some silicone O-Rings and reinstalled the shaft and Teflon back into the carb body. The brass shaft is very yielding to filing cuts easily. This’s could be carried out in a afternoon easily. If you want a cleaner idle this may be worth your time. My first attempt last year was just installing O-Rings up against the carb body ends by side loading with washers. This seems to be more effective in sealing the leak. The carb body ends have a slight bevel to it and the O-Rings fit in nicely.

[nismou20]

Oh, and if you want to go the extra mile you might try this.

[Nissanman]

Very clever of you
I have often thought that something like that would be a practical fix.
What is the reason for rounding off the base of the slide?

[nismou20]

Radiusing and thinning throttle shafts are tips borrowed from the SU racing world. These combinations increase speed of air over the jet bridge for better performance. Since engines are just big air pumps I figure it’s a win win. Between shifts at high rpm the car is sucking so much vacuum it feels much like the boost coming on in a turbo that it pushes you back in your seat. I’m running a stock Cam, +60 bore, with the reworked SU and it has been transformed.

[Solex68]

Great info! Thanks for the write up.