Enforced restrictions

In order to get a motorised bike through the Single Vehicle Approval test here, I will need to actually reduce the output of whatever engine I use down to 1kw or 1.3 bhp. Since this will be a 2 stroke, there are several ways I can do it, but has anybody else had to do the same thing, and how did they do it?

I think at the last count, it was £85 and about a third of that for a retest. Looking around, I've found a petrol scooter engine at 50cc that has a reduction gearbox on it and uses 8 mm chain in sensible sprocket sizes. I think the simple way of putting a spacer in the carb to stop the slide moving too much will be easiest; add a restriction on the silencer as well and it should be on the way.