413 Motorhome not starting

The basics, compression, fuel spark

COMPRESSION: Has the engine been sitting? Put a squirt of oil in each cylinder. Won't hurt to run a compression test while the plugs are out Are you sure it's in running condition, timing chain, etc?

FUEL: Need fuel, l FRESH fuel. If any doubt as to whatever can you are using get some fresh. I've started engines with NO carb, just throw a tablespoon down the manifold it should fire

SPARK: Need a good hot spark, and IN TIME. Check spark with a solid core wire at the coil. When cranking, should produce at least a 3/8 and typically 1/2" long hot blue spark

You have a timing light? You can check timing on the starter

Is this installed or on a stand? How about battery voltage? Cranking voltage needs to be bare minimum of 10V or more under load