phear8me wrote:....why dont you look at dropping a 900 top end on it? .
i mean if your looking at complete top ends or rebuilding one why not go for a tad more power while your at it?
because from memory the 750 900 and 1100 share the same bottom ends but dont quote me on it

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nothing like that at all mate.
The 650 and 750's share a lot of the same engine architecture, and you can turn certain 650 models into 750's easily enough with a top-end swap..........but that is where it finishes for the smaller models. Some of the 650's can't be changed to 750's due to cam-chain design....you can fit big-bore kits to these though - MickLC's 'Silver Surfer' has a 720 kit for example. The largest kit for a 750 motor is the 810cc Wiseco kit.
The 900's and early 1000's have the same bottom ends (well, similiar enough to allow swapping), but the later 1000's have different bottom-ends, and the 1000J and 1100 models are different again from the late 1000's. (Cam-chain design being the biggest difference).
The only thing that the 650/750/900/1000/1100 motors share - is the cylinder bore spacing. You can swap carbies (but need the correct inlet manifolds) between all these models no problem. You can fit an early DFI system (injector rack & butterflies) from an 1100 to a z650 or z750 easily - they bolt straight up.