In an effort to eliminate or reduce the on / off and off / on buck that I was getting, I took the bac valve off and carby cleaned it. There was bugger all to clean, but it's smoothened the car up quite noticeably. The on off throttle buck is no longer my biggest annoyance with the car, it's quite minor now. Just thought I'd let anyone interested know

 

you mean that shutter when you let the gas off?
that's cool. it's really annoying, especially during traffic jams, it;s like you're riding a hourse@!

 

that's the one. It's certainly worth a try anyway, though it still does shudder, it's reduced...

 

Be sure to apply voltage to the Bac Valve, (more like on/off repeatedly) awhile working In the WD-40 or whatever allowing to work the valve In and releasing any sticking points.