Engine Not running

I have a craftsman 17 hp model 917.271653 riding lawn mower that is giving me fits and would appreciate all the help I can get. I tried to start it a few days ago and of course the gas cut off valve didn't get cut off the last time it ran so naturally it wouldn't start. Cleaned the fuel tank, changed the carburetor with a new one and it started up. I started to mow the yard and got only two rounds and it quit and wouldn't start again. I checked the ground wire and they were okay so I let it set and tried it again and it tried to start but quickly stopped again. Changed the spark plug and finally got it to run once more but only for about 5 minutes. Checked the fire from the plug by taking it out and laying it next to the engine block. It had fire but it was of a light yellow color. I was wondering if it might be the coil or something else I need to replace. Any help will be appreciated,

Sincerely,
Labrauer:confused2:

An engine make & model number would be an immense help.
I gather the engine was full of fuel.
Did you check the oil level.
If it is suddenly too high or smells of fuel change it and the filter if it has one.
Refill to the proper level.
If that is a gravity feed engine, buy an in line fuel tap & fit it before the fuel filter so if nothing else, it will make fuel filter changes easier & cleaner.

Air filter ?

God bless
Wyr