All sorted today, thanks to Zed! First he set the timing spot on, then took the linkage off and adjusted the throttle stops until we had a steady tickover with the least amount of shaking. Only then did he put the linkage back on, and adjusted until he got the same readings from his flow meter for both carbs. The van is now noticeably quieter and smoother. I filled her up and noted the mileage in the van notebook- it will be interesting to see how much mpg is improved, Zed said the exhaust smelled of fuel when we turned up. Covid seems to have killed my sense of smell forever, so don’t ask me! Thanks again, Steve.
Nice to meet the Davos today, do some easy tinkering, spot of lunch - lovely. Timing was a couple of degrees too advanced, set that. Rough balance wasn't happening, more later Disconnect linkage one side Rough balance and slow it down on the stop screws... a lot Rough mixtures (one turned in about 6 turns, other 2 or 3) More balancing Mixtures in more Balance Mixtures again. Balance again. Probably more times than that until I couldn't get it any better, engine sounds healthy. Held linkage up to reconnect, it was getting on for 10mm short - that how out of balance it was. Reconnected, balance opening by eye/ear. Done. Pretty easy to make a good improvement when somethings as far out as this was and that's a nice feeling. If it were mine SVDA distributor Stock exhaust Check jetting and emulsion type installed and go from there. I suspect it's not right and you'll get plenty advice on here about what works. First you need to know what you have though... and to find out you'll be disturbing the linkage. It's one reason I prefer the centre pull ones - not mounted on the carbs.
Zed at work: Bays in the marina: If I had a SVDA distributor where would I get the vacuum feed from, is there a blanked tube anywhere on the carbs or manifold?
I didn't actually check but I'm sure there will be, probably one on each carb though you only need one. Mine needs it's yearly wash!