You said you have spark. It should be white in color Yellow would be a weak spark & may be your problem. For the stuck screw try putting your screwdriver into the screw & hit the end of handle driving into the screw. This will help set the driver into the screw for a better bite & also the shock/harmonics will help to break the screw loose. I usually do this to all the screws when working on small carbs, it really does help to not strip the screw.
If you spray just a little shot/for 1 second, of carb cleaner into the intake while cranking the bike should fire. That will help you figure out if it's fuel or spark.