Anyone with Keihin CR carbs on Z1/Kz?

[Streetfighterkz]

I just purchased some nice, used Keihin Cr31’s from eBay for a Kz900 based trackday bike I’ve been gathering parts for.

My question is: anyone have first hand experience using the CR’s on a Kz? I have a set of MTC 1075 12.5:1 pistons and a pair of Gpz1100B camshafts. I’m still looking for a ported head in good condition to round out the top end.

Any help/guidance will be appreciated.

Later, Doug

 

[kopcicle]

Okay Doug, you opened a can of worms and opinion. This is more a question of diminishing returns and reliability than "a ported head".
There are three heads (other than the DFI head) the open chamber small valve, the open chamber large valve, and the "bathtub chamber" (also small valve) head.
Forget the bathtub chamber head. It's rarer than an honest politician in an election year.
Porting. Why? the "j" 998, 1198, head has ports marginally too large as it is. The best thing to do is carefully kill the casting flash and match the carb holders to the intake. If anything extend and flatten the intake port floor. The exhaust gets a polish only to give carbon nothing to hold on to.
Back angles on the valves, radius or multi angle valve jobs, opening the bowl area are a total waste of time and kill flow and velocity.
Smoothing the short turn radius is best left to a flow bench but marginal gains can be had if you're careful.
The stock valves are in a word , soft. Honestly that's too gentle. They are garbage.
Shim over bucket is metallurgical destruction waiting to happen. Swap the KZ650- 750 shim under bucket pieces in and buy the shim kit. You'll need it.
I could go on. Do you want to know more ?

 

[Streetfighterkz]

Thanks for the info. I’ve also been collecting parts for a 1428 13.5:1 prostreet dragbike build so I have some knowledge.

I was wondering more about the carb sizing for a bike running higher in the RPM range. I will most likely drop on a J-model head to lower the 12.5 compression ratio down some.

Later, Doug

 

[Out]

Pretty sure I have a J head ( whole engine with a hole in piston #2 ) here somewhere if you are interested.