My recently acquired 1979 KZ400h LTD has tube type tires mounted on cast wheels, with no inner tubes. I have been having to add air every few days, and have found the cause has been air leaking around the rims. I have always thought cast wheels took tubeless tires and do not require tubes. However, Partzilla is showing inner tubes with these wheels.
So what are the rules.
Can I mount tubeless tires without tubes on theses wheels? Or tubeless tires with tubes? Or tube tires with tubes?
Rims that are safe to run tubeless will usually have TL cast into rim or spokes somewhere, generally near other DOT markings or size markings. Some early variants may not have this casting. Tubeless safe rims will have an extra lip on the inner face to keep a deflated tire from coming off the bead. If this lip is not there, rim should be run with a tube. I am not sure what model year Kawasaki started adding this lip to their castings...roughly around 1978. There are lots of threads with pics on this topic here if you search...can be a controversial topic
My 750 came tubeless from the factory. The rear wheel has the extra "tubeless bumps," but the front doesn't. I had an early 1980's vintage Suzuki GS that was the same. I take this to mean, that the extra tubeless bumps are not a strict requirement in order to run tubeless. And there are tons of guys that converted their tube type "mag" wheels to run tubeless. Installing the proper valve stem is an obvious requirement. Surfacing the wheel, so the valve stem sits on a flat surface, may also be needed. Whether this conversion is a good idea is not a clear choice. There are pro's and con's both ways.
When the tire was fitted did you or the fitter use any rim seal?
It doesn't take much corrosion or muck on the seal face to cause an air leak. You say it takes a few days to loose some pressure so guessing it's not a big leak.
First thing I would do is remove the tire, carefully clean the rim seal faces, re fit the tire using plenty of rim seal and see how you get on.
Adding a tube to a tubeless rim that doesn't have rim/bead locks would be the last thing I would do. Seen several occasions where the tire has slipped on the rim ripping the valve out the tube and instant flat tire.
I'm running Michelin Commanders tubeless on a KZ440 for a couple of years now.
Biggest problem...mounting the tires.
The beads took forever to seat and it's still not perfect.
I've pumped the front tire up to 70 psi in the summer to get them to fully seat. It didn't seat evenly.
The front has a very slow leak.
Back is fine.
It is a very controversial subject. Do your research.