Nothing on a std '28 is geared towards decent top end power or speed;

Pipes are restricted, Dremel and patience or race pipes.
PGMIV is retarded, '21 flywheel or HRC card.
Barrels are ported too low, port them or fit 21 barrels, very little difference really but it is there.
Carbs are annoying to work on, 21 carbs or live with it.
It's only geared for 115mph, change it or live with it.

My '28 roadbike has the std pipes opened up, std card, an entire '21 engine including carbs fitted and is as quick on the road in real life as any other 250/400 grey import bike from the same time.

On the plus side the engine does swing up into place on the '28 if you get the rear mount bolt in first making swapping motors a doddle and it's as trick as a trick thing doing a card trick
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