Got an old C500 and cannot get it to start. Have spark and compression with a good vacuum on the air cleaner when cranking. Am getting LP vapor to the carburetor but doesn't seem to open. Took it apart and cleaned, checked diaphram which appears to be good. Looking for advice on getting this old Clark moving again. It may help to just explain how this system works. It is an Zenith carb replacement on a Waukesha engine. Thanks cook