Why are kits slower than my GP200 I had in 1973

[Tractorman]

I was clocked doing 71 down the A46 by a police car on mine back in early 70's.

[Rich Oswald]

I was clocked doing 71 down the A46 by a police car on mine back in early 70's.

Cops had Veglia speedo's too ya know!

[Warkton Tornado No.1]

leaded petrol...plus the fact I now weigh twice what I did back in the day

My old stage 4 200, PHBH30, JL3 with SX gearing once wound up would hold 73gps all day long at 600/650 0n the Egt (LI Crank and motoplat ignition) but since shearing the crank I just cant seem to get those speeds again

Aren't motoplat flywheels heavy, which would explain holding top speed when you got there ?

Good point...could well be the reason

A heavier flywheel will have greater inertia but that doesn't contribute to the ultimate top speed. Flywheel weights are very 'swings & roundabouts' & personally, the Lui/J/AFR electronics are as heavy as I would go, making for snappier acceleration & much more forgiving toward the crankshaft & transmission.

Part of a rider's problem is often that they expect the power delivery to be like that of a four stroke car which explains why they shut the throttle descending hills, the consequences often being leaning off in top gear with less fan cooling

[GExS]

I ran a standard one a few years ago, and was shocked how quick it was, I heard some were quicker than others that’s 2 strokes I guess. It had new tyres on, front fork rubbers and springs which may have helped it otr, back in the late 70’s early 80’s we were pulling them out of sheds and ran them as they were with old tyres etc.
The one I ran made me rethink standard exhausts and 22mm carbs and I’ve only used them on set ups since.