GPZ810 Engine Build

Hello guys, 

I am currently looking in to building a 810cc engine for my GPZ750 Unitrak. 

After all bearings and chains have been changed, it’s gonna be an engine build with the following setup:

- Wiseco 810cc pistonkit at 10.25:1 CR
- 4-1 Kerker exhaust 
- Dyna ignition with coils 
- Standard cam and valves
- Ported header

My question is, what set of carbs would you suggest? Mikuni RS34? Keihin CR31 or CR33?

The engine will of course be dialed in on dyno by a known Kawa guru in DK.

Hope you’ll be able to help! 

See the picture of the bike so far. 

Best regards 
Peter

Bike looks real nice 

I have to suggest the Keihins. The 33s will probably suit you fine with the stock cams. I put Mikuni RSs on my wife's bike & because of the flat slide design, they have a very strong return spring and she comments ( ) about the difficulty in maintaining a constant throttle position. The CRs on my bike don't require the stiff spring. However... YMMV! 

And the wookie is right! 

Bendix94 wrote:

Hello guys, 

I am currently looking in to building a 810cc engine for my GPZ750 Unitrak. 

After all bearings and chains have been changed, it’s gonna be an engine build with the following setup:

- Wiseco 810cc pistonkit at 10.25:1 CR
- 4-1 Kerker exhaust 
- Dyna ignition with coils 
- Standard cam and valves
- Ported header

My question is, what set of carbs would you suggest? Mikuni RS34? Keihin CR31 or CR33?

The engine will of course be dialed in on dyno by a known Kawa guru in DK.

Hope you’ll be able to help! 

See the picture of the bike so far. 

Best regards 
Peter

The stock BS34 Mikuni's were used on all kinds of KZ's, including many 1000 and 1100cc model bikes.  Do you think they would be a bottleneck on an 810?  

Thanks Slayer61

but would I get better performance from the mikuni flatslides father than the keihins roundslides?

you did mean ported head & not header ? I have done some of these back in the day I would use Mikuni RS34
 

Nessism

The stock Mikuni are CV vacuum carbs, which I would father avoid on the 810cc setup.

Thanks wookie58!

Yes I meant head! 

and the RS34 is quite okay to dial in? 

I’ve read somewhere that the Keihins should be a lot eaisier? 

Bendix94 wrote:

Yes I meant head! 

and the RS34 is quite okay to dial in? 

I’ve read somewhere that the Keihins should be a lot eaisier? 




 

I think its the other way around, probably more brass involved tuning Keihin CR's than Mikuni RS, flat slides probably more forgiving in the mid range (or you don't notice it as much)
There is nothing wrong with the CR's, fine choice, but if it was me I would go with the 31's over the 33's just based on engine components.

You don't need to port that head, its already has huge ports. You would be better off just port matching to the manifold rubbers (go in about 3/4") I would spend the extra money on some decent cams in the .370-.380" range if you really want to wake up the top end. The carbs alone are going to give a good power increase.

To injected,

Okay, so you would go with the Mikuni RS34 flatslides?

That means it is nessercary to port the intrance of the inlets a bit? 

what range is the standard GPZ cam in? and will it still be street rideable?

thanks!