Engine is sputtering and losing power

[Dq3]

I have a Craftsman riding mower. It has a Honda 16.5 hp twin cylinder engine. Model # 917.273500. We have just replaced just about everything on the mower. Here is the list,
New fuel tank, new fuel lines, new fuel filter, new fuel pump, new spark plugs, new battery and blades. Mower starts and runs great and sounds great, then after about 20-30 minutes it starts sputtering, missing and losing power. I look forward to any help, suggestions, tips anyone has.
Thanks
Dan

 

[Carscw]

Could be your gas cap is not venting. It needs to let air into the gas tank

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[SONOFADOCKER]

Heat issue can be a few simple things . Re check fuel lines for sucking air . Your coil can be cracked or failing for the spark plugs . You can try to drizzle some Sea Foam into the carb when the tractor is running to remove carbon build up on the head . A hot cylinder head from carbon will ignite the fuel before the compression stroke is complete - loss of power ...

 

[Dq3]

Thank you for replies. I will try both of these suggestions. I will report back what I find.
Thanks
Dan