I am referring here to older ATV's with carbs. I have had problems on and off with my ATV not starting, won't idle, battery not enought juice to turn it over, etc. I finally hit on a regiment that keeps my ATV starting and running like a champ. I hope this helps someone else:
1. Never use gas with Ethanol
2. I ALWAYS add Sea Foam to the gas I put in my ATV. This is some of the best stuff ever invented!!!!
3. I bought a $12 Trickle Charger (it has a computer chip in it that will not let it overcharge your battery) and keep it hooked to my battery year round.
4. Start it up about once a month and let it run til it warms up good. (Really with the other 3 steps, I do not think I would need to start it that often.)
After years of aggravation, I haven't had any problems since I started this regiment.