[Kawasakian]

If you add a piece onto the existing Spring, 1st make a tiny loop so when it pulls, it will hold, do that to both ends, then you could solder the two pieces together and get it to work. I've done this on a lot of lawn engines that have that same long spring set up. Kind of a hack, but works. The other way is to go to a really good hardware store, the really old kind, and search their spring inventory, I have found springs like that, sometimes too long, which is better than too short. A Kawasaki dealer may have something like that sitting around, especially an older one.

 

[Kawasakian]

Check out this link. Scroll down to the bottom. I think if you look by measurement, you should be able to find something.

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[Kawasakian]

If he's that cheap, then uncoil the spring with some needle nose pliers till it's long enough, and you will get it working.

 

[Kawasakian]

You could always swap or drill the jet up one size, on the Chinese carb.

 

[Kawasakian]

Usually popping in the exhaust is unburnt hydrocarbons ffromt a lean condition. You could spray ether from the end of one of those little red tubes, to pin point an air leak, barring none, see if you can lift the needle one notch. Not all carbs have the notches for doing that.