Possible Iggy Trouble

I am using my rd 400 as daily runner. I’m not quite 100% happy. 

It’s been restored motorwise completely last winter.

It ran well for a couple weeks and then probs crept in. 
It seems to pot-pot-pot more on the LH side and the exhaust downpipe is also turning blue (there used to be small streak of sludge running down it too, that has stopped)… it also killed a plug one cold morning when i gave some strick from cold. The other pot runs quite happily and has a more metallic sound to it… more like a 2stroke pipe.

PROB N1 Both my plugs look like this: 

The external electrode is quite like in the pic, not white but lighter (very light choccy color) the inside electrode also has a ring on top of the same color. Rest of the plug looks rich (safely).

I reset the carbs, synched them (oilpump too, off by a mile) reset points and put fresh plugs later. The syncing didn’t seem to make a lot of difference, but the new plugs did. I’m running B9ES, but am doing a lot of town work and partial throttle.

Advice gents?

Should I change plugs (B8ES?) Retime the whole thing?