Got a question about '79 KZ400 carbs

I have my bike taken down quite a bit at the moment, I've resolved not to ride it again until after I've accomplished a few things with it.

The carb diaphrams have holes in them, at the top. I've planned to ship them to NRP carbs in England to have new diaphrams fitted to the slides, because I've tried "patching" them with no real success, and I'm convinced that this is the reason I don't have any high-speed power. There just isn't anything there at 60 mph, 5500 rpms, and 3/4 throttle. I can roll on the rest of the throttle, maybe coax it up to 70ish mph, and sooner or later the motor will just quit, to come back alive again after some coasting, usually with a semi-trailer up my rear. It's weird, this thing has plenty of pep off the line.

Between the energy bill and my wife's pregnancy, I can't really justify the expense right now. (Approx $125 USD) I know, that's actually a good price, but I'm not 100% sure this will solve my problem.

Here's what I'm wondering: Is there such a thing as an aftermarket carb for this bugger? Hubbout this: What if I found a 440 top end for the motor and bolted that on? Are the carbs going to have a different design, hopefully sans hole-prone slide diaphragms?

I've had this bike for 2 years now and doggone it, the next time I fire it up, I want to be able to redline it to 90 mph. (read BE ABLE TO)

What are my options?

Thanks yall

For some reason I thought I remember something else that would work. I wont remember it as 400s arent my thing but it should be in the archives.

Also check out www.kz400.com

I asked about that so many times
Those carbs really are trouble aren't they? Especially if they've had fuel sitting in them eating the carb body away for a good long time. I never got a solid answer. I've heard of a lot of people replace the KZ400's carbs, but not anything but a different CV (constant velocity - read--they have those diaphrams that are very fragile). I know there was one guy selling a KZ400 motor with a Yamaha XS400 carburators. The KZ440 has a very similar carb design, but yea it is different, and yea it is still CV. It's a great performance mod, but I wouldn't expect that it would make your like ANY easier :evil:
Basically speaking, as you move away from the stock setup, your life will only get harder and more expensive. Unless you got a bunch of carbs just lying around at a friends house and don't mind screwing around with it a lot.


I personally would put money on torn carb diaphrams causing SERIOUS performance detriment and possibly even engine damage.

The good news is that the 400 is only a twin, and finding decent parts carburators shouldn't be a problem. I bet you could get 4 parts carbs (2 sets of carbs) for less than 125 US, and I'm willing to bet that at least two of them would have good diaphrams. Also check any junk yards in your area, of course.
Here is a trick I used on my 400, I coated the diaphrams with wheel bearing grease to make the material more flexible. That way, I never had any trouble with my diaphrams.