1. Sprocket alignment or chain too lose. You want your wheel sprocket to be lined up with the sprocket on the engine. You should have from 1/2 to 3/4 inch of play in the chain. Also be sure your rear sprocket is centered on your wheel. When you spin your wheel, look at the top of your sprocket...does it go up and down? And also make sure your rear sprocket is mounted flush, meaning it does not wobble.
2. I have used a ATV thump throttle, or a motorcycle throttle would work as well. Any local motorcycle shop should be able to help you out with that.
3. I hit the tickler (primer) on the side of the carb about 6-8 times, I have a on/off switch so I make sure it's on. Then I pedal between 7-10 mph and let the clutch go and
I am off running. You may need to use your choke, try half way first.
4. Make sure that your throttle cable is nicely lubed and try not to kink the cable. Zip tie onto the bike in too many spots will make it stiff as well. Look at the pic below to see where to adjust the throttle cable.