Hey thanks for the response @CONROD , apologies for not noticing your reply sooner.
The engine is as standard as can be. Though if I recall the bloke who did the machining for me took it to 1st oversize. I did the build in 2019, so I've forgotten. But it was about freshening a 500 000km engine, not a performance build.
No back firing. Just a burbling bubbling sound when I decelerate. I just wondered whether the decrease in exhaust pipe volume half way along my have something to do with it?
After reading the crawler post I think I'll add a whisker of fuel to the idle circuit and see what that does. It idles fine, but as I read over and over again, a little too rich at idle does not hurt. I think the carby is jetted pretty well as part throttle cruise is close to perfect (or what's been suggested in other forum posts I've read)?
The AFR Gauge is an AEM. Nice kit, but it came with the standard 10 second USA warranty. So when the Bosh wide band died after only 8 months they would not replace it.