KZ440 single carb, how do you keep carb intake boots from splitting?

Hello all. I have an early KZ440 that has a single carb conversion. Basically, two aluminum "U" joints welded into one "Y" tube the carb attaches to. I keep cracking and having to replace the carb intake boots because they support the weight of the carb. With a little bit of downward pressure from the Carb location and road bouncing, they split. What are you guys doing to support the carb so the rubber intake boots don't crack?

What are we doing? We are using one carb per cylinder as nature intended.

I have seen pics of the single-carb manifolds, and I think the issue is the length. Think of the distance from the cylinder head to the carb as the length of a lever, because that's basically what it is: a lever acting on the carb boots.

In the stock setup the carb's weight is quite close to the cylinder head, so there is comparatively little leverage/stress on the boot; IOW the carb is on a very short lever, so there is less stress on the boot. Stock carbs are also supported on the other end by the airbox; your carb doesn't have that support here.

The single-carb manifold is much longer than stock, so the weight of the carb is supported at the end of much longer lever. IOW the weight of the carb has more leverage and places a lot more stress on the boots.

I think you have a couple options.

1) Go back to two carbs (stock, Mikuni VM30, whatever). You indicated that the single-carb manifold doesn't really fit anyway (since there's downward tension on the carb all the time).

2) Tighten a wide, flat hose clamp around the boot between the carb and the head. You may take enough flex out of the system to allow the boots to survive longer.

It looks to me like the intake boots (black ones) are being really squished down to a reduced diameter. That may be contributing to the splitting. Maybe you can braze on spacers to the outlets of the Y pipe so the diameter matches better. As far as the carb pulling down, that should be easy to support with a small rod etc attached to a bowl screw or something. I'm assuming you have some sort of Mikuni VM carb on there.

Somebody didn't give that mono-carb conversion much thought. I would consider switching back to the stock carburetors or fab up a properly sized manifold. For support I would check the frame to see if there are any unused bolt holes available to attach a homemade carburetor support bracket, then rig up something, preferably w dampers. KZ carburetors are mounted in rubber carb holders & rubber airbox ducts, so the stock configuration is kind of dampened.

martin_csr wrote: Somebody didn't give that mono-carb conversion much thought. ..............

Exactly! Ed

I'm assuming the po got the bike that way & I don't mean to insult anyone. :blush:

650ed wrote:

martin_csr wrote: Somebody didn't give that mono-carb conversion much thought. ..............

Exactly! Ed

Someone thought about this one; I saw it in a CL ad. :huh: :blink: