Carbon Monoxide or CO is formed by combustion in an over rich mixture. The idle screws will only lean the mixture at idle. If your engine failed at part throttle, it cannot be fixed with the idle screws. It may be due to some problem in your carb or intake. Do you have a clean air filter?
Is your carb float setting or your fuel pressure right?
What color are the plugs? Do they show a rich mixture?
How is your Hydrocarbon reading? Rich mixtures should also produce high Hydrocarbons.