KZ650 vs. KZ750-4 Heads?

650- intake outside 36.1
intake inside 26.3

kz750- intake outside 40
intake inside 29.5

hope this helps. its warm out today so i have to take her for a ride. Any way u can get the combustion chamber diameter from a head gasket?I dont have another gasket so i dont really want to pull the head off (not a fan of reusing them). keep an eye on ebay for a kz750 head, i scored mine there for like $25 with valves, liters and all+ ship (the price of the new cometics gasket im guessing). even if u end up with a zr head, the kz head wont go bad sitting on a shelf! but im sure someone on here has a kz750 head sitting aroud, not on the bike so they can get the cc diameter.
-patrck-

Since you are going to 810cc I presume that you are going to use 750 cylinders, are you not? I have some dimensions for you. First of all, every bolt hole lines up between a KZ750 head and a ZR750 head. Every dimension is identical. I also believe that the difference between the KZ650 head and KZ750 head is the same as the difference between the KZ1000 head and the "J" head. This being the cam chain and upper idler. Talk to APE Jay and he I believe will tell you that the cam chain idler modification is the same. I will email you all the pictures.

Thats awesome guys, thanks. I think I may try out the ZR head, if I need to mod it a little I can. But I'll be keeping my eye out for both, no reason not to get a cheap KZ750 head. Theres even a guy locally with one but if it doesn't have the top idler mounts then ebay it is.

I PMd you if you want something to experiment with.

So. I've been doing some investigating, and it seems the late CSR heads have the same valves as a KZ750, along with the fact that they had BS34's as stock and the cam upper idler mounts. Maybe this is my best bet?

Actually, the difference between the 650 & 750 heads is 10CFM stock at 10" of test pressure. The 750 also has 1mm larger intake valves. I've ported both types.

83 GPz 750 head has yet 1mm larger intake valve and probably flows more than the standard 750.

As for the 750 Zeph head, I have never had one in my hands so I can't tell you what it flows or what the valve size is.

If a guy wanted to go with an 810cc motor based on a 650 bottom end, a freshened up, lightly ported 750 head would be the one to bolt on for a street motor.

Just don't go overboard on cam duration or carb size.

29mm Keihin CRS carbs would be a good carb choice for something like that.

Here's a pic of the last 650 motor I did.

Ok Larry, I know we've been through all this a thousand times, I'm just way too cautious.

But I did look at the parts diagrams and the 650H2/3 uses the same exact valves as the KZ750. Maybe they went bigger later on? I just don't want to have to fab up a top idler assembly like one that they use for the KZ1000J.

In any case, a head will be coming your way soon.

Anyways, I guess I'll hold out for a KZ750 head which has the top idler provisions. Thats my best bet I think.

I wish I read this thread before I bought an '80 head.

You have to be much more specific so we know what the problem is.

It sounds like the ZR7 or GPZ head would have been a better. I plan on sending it to LarryC as soon as I get it.