If that doesn't cure it, it might just be a matter of re-seating the slip-ons to get a better seal...
Arrived, fitted and bike still starts/ticks over. Fingers crossed for a dry Saturday for a test run..................
Well that was £35 very very well spent. Not one proper bang in 40 odd miles, 1 or 2 little almost pops but nothing like before. And much much less snatchy in town and tight slow junctions and round abouts. Tip top.