So, a few years ago I ran out of talent while Visarding my HIF6. I managed to countersink holes in the throttle disc off centre. This made the disc not close when it was screwed to my cut-away throttle shaft. So I went to the local carb place and got a new disc.
Trouble was that the new disc closed at a different angle than the original. The new one was more eliptical.
Time passed and I needed to re-kit the carb due to dodgy shaft seals etc. I got on to SU Midel and explained that I needed a new disc and that I wanted the one that closed at the right angle. I must admit they didn't sound like they believed me. Well, wadda ya know, I got another wrong disc. The shipping note said that I'd got an HIF6 rebuild kit but and HS6 disc.
Here is the difference:
The HIF6 disc is on top. It has a 5 on it so I guess it closes at 5 degrees to the carb bore. The HS6 disc closes at many more degrees. Using this one gives a short throttle throw and means the choke mechanism doens't interact with the throttle correctly and the idle-up doesn't work right.
I have now put the original disc in but use botton head screws and flat washers.
So there you go. The guys at Midel have been in business since JC was a boy but didn't know about this.
I hope those of you running HIF6 carbs have more talent and luck than I do. And, if you need a new throttle disc, make sure you don't get one for an HS6.
M.