fuel additives

[Keithver]

Tim. Apologies up front. When i took it for a good run, it felt as if I had lost half my throttle.
I had visions of re-setting the cams to stock initial position and keeping quiet.
In fact, that's exactly what had happened. I HAD lost half my throttle.
(Photo 1) shows how the "stop clip" at the engine bay firewall had pulled back the black plastic coating and pulled the steel inner through the firewall.
The clips where what was on the old cable when I got the car. I simply reused them. Is there something that goes onto the cable housing to stop it pulling through, I don't see anything in the parts book.
I made a stopped nipple to hold the casing in place and stop it being pulled through in photo 2.

I took her out for another run. Chalk and cheese.  She revs beautifully and pulls wonderfully.
Unfortunately, I still have the stutter. I'm thinking it is probably the carbs