Found this Technical Manual for Honda GX240 through GX390 engines.
There is lots in it.
A some things covered are:
* Recommended Power Range
* Output Confirmation Methods
* Minimum Cooling Air Flow Requirements
* Maximum Operating Temperatures
* Ambient Temperature Limits
* Engine Enclosures
* Engine Mounting
* Resonance Check
* Power Transmission
* Wiring Diagrams
And more...
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