Slant dies when put in gear.

Sounds like carb to me. If the idle is too high, the sudden drop in RPM when you put it in gear can make the engine stall. (not to mention the strain it puts on the rest of the drivetrain) You should be able to bring the RPM's down to 500 in neutral without it stalling or running rough. It it does, try to readjust the mixture to smooth it out and try again. If adjustment won't do it, you probably have to pull it apart, clean it out, and put in a kit.