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Thanks...... appreciated........I had naively hoped I could avoid the mysteries of tune ecu...but this looks unlikely now.
It's that low speed snatch that irritates.
There's a chap on the RAT forum reckons on reducing this by reducing final chain slack to 13-15mm ( whatever a millimetre is..damn foreigners)....sounds a bit radical to me...anyone here tried it? If so, do you still have an intact crankcase?



On the wifes 2012 SM, I tried a handful of remedies to address that low speed surging. Including adjusting the chain, both tighter and looser, even re-gearing. I played with the tune and was able to make it better but not entirely fix it. (see the tune section)
after mucking around with it for way too long, the final fix for it was to buy a pieman tune, loaded that and all good.

05 speedmaster - 1100cc, 11:1 racing pistons, Carillo rods, thunderbike cams, ported and polished head, 2mm over intake and exhaust valves, Barnett kevlar clutch, scepter pipes, oversize manifolds, 45mm HSR's, TTP stage 4 firestarter