KZ750 - GPZ750 motor interchangeability

[chrism2352]

Does anyone know how I can find out whether the cams, carbs and possibly the head from a GPZ750 will be a direct fit to the rest of a KZ750? I've been told that the GPZ750 has higher performance cams and carbs, so I'm thinking about getting a set to put on my KZ750.

Where would I find out the specs - center to center distance on the carbs, cam length, etc. - for these two bikes?

thanks,
Chris

[MFolks]

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9.Carolina Cycle - KZ / GPZ / J Model

[steell]

Just ask

Center to center distance on the carbs is the same for KZ650, KZ750 four, KZ900, KZ1000 (including the Police bikes all the way to 2005), KZ1100, and their air cooled GPz variations. Water cooled models are different.

83-85 GPz750 cams have the most lift and duration of any 750 cam (650 and 750 cams interchange), but I have read that some have a smaller base circle, those would need either some thick shims or the valves sunk in the head. 83-85 GPz750 head is supposed to be the best flowing, and will bolt on the KZ750 block, but you'll lose the tach drive (GPz750 cams have no tach drive gear).

Don't even think about GPz750 Turbo parts, that's almost a different motor, head and cylinder block will interchange but not much more.

[AgentBauer]

I was just wondering what year your 750 was chris, I am working on a 1980 750 g. Perhaps we'd be able to share some useful information with each other. Keep in mind that I am no mechanic or Motorcycle Jedi like steell appears to be, but I am working on it.

[chrism2352]

Agent Bauer, I have an 80 KZ750 E1 and an 81 KZ750 H2 (or H1, can't remember right now).

Steell, it sounds like a complete gpz head and cams might be the best way to go, rather than worrying about whether the cams will fit in my KZ head.

[elr658]

No, a complete GPz motor is what you need. The change in performance between a silver motor and a black motor isn't worth the $250 in gaskets you'll waste.

[AgentBauer]

I don't know if you have one or not, but I have the haynes manual for your bikes if you want it. I have the twin, and the book covers all of the fours. Figures.

[chrism2352]

Thanks Agent Bauer, I already have the factory repair manual, and that's been pretty helpful so far. If you don't have a use for the Haynes manual, though, I'd gladly take it off your hands. Also, I noticed you were looking for a seat...I have one to my '80 kz750 E1 (4) that I won't be using. It's in excellent shape, and if it fits your bike, I'd be willing to let it go for a good price.

[steell]

Originally Posted by elr658

No, a complete GPz motor is what you need. The change in performance between a silver motor and a black motor isn't worth the $250 in gaskets you'll waste.

$250 for a top end gasket set, or base, head, cam cover, and 4 exhaust gaskets?? Less than $100 is more like it, a complete Vesrah gasket set cost me around $80.

Installing a 83-85 GPz750 in a KZ frame involves a new clutch cable, new throttle cable, manufacture of a spacer or two (stacks of washers look so ugly), and, if you want to run 530 chain, sourcing an offset sprocket. And a bit of wiring modification.

Howsomever, if I was going to do this, I would shave about .030"-.035" off the cylinder head and slot the cam sprockets. That will increase compression and the slotted cam sprockets will enable the cams to be correctly timed.

And then there's the most expensive words used when working on bikes.
"While you're there", I'd go ahead and install an 810 kit from Wiseco, less than $500 for the kit and less than $200 for bore and hone. It's only money, right?

Look at it this way:

It's cheaper and better for your health than drinking or doing drugs, cheaper than weekly counselling sessions, and if it keeps you from killing someone, then who can complain?