Onan Marquee Generator wont crank with plugs installed?

I experienced this phenomenon on my neighbors lawn tractor.

Most OHV engines have a "built in" compression release on the cam shaft. The compression release is a slight tap on the exhaust valve during the compression stroke and will drop out after the engine is running. If the exhaust valve has too much clearance, the compression release will not function.
I don't know if Onan uses this technology or not.

Richard