you put a walbro pump on it? if so, did you use the orginal sock or the new one that came wth the pump?

from what i remember about 200's and their pumps, there is no resistors at all inline or whatevr with the pump - it sees nominal battery voltage all the time.

best asking on the sxoc.co.uk forums tho.

det at high revs might be to much advance on the ignition curve - get it booked in for a setup somewhere reputable - like Stu