Idle ATC Problems in a Hondaby John Willis
Honda has manufactured a wide variety of all-terrain cycles, also known as "three-wheelers." While Honda's ATCs have been made in four-stroke motors, two-stroke motors, racer versions and utility versions, idle problems are almost always cause by the same issues. The most common problem is carburetion.
The function of the carburetor is to mix the appropriate ratio of air and fuel, not just at idle, but at every throttle position. Honda carburetors have multiple fuel circuits. Each circuit mixes the air/fuel ration for a different range of throttle position. Each circuit overlaps so there is a smooth transition in fuel mixture from closed throttle (idle) to wide-open throttle.
Do Not Re-jet Your Carb
Many enthusiasts are aware that changes in altitude, temperature and even barometric pressure affect their fuel/air mixture. In particular, increasing elevation reduces the amount of air in your mixture, thus increases the use of fuel; higher elevation makes your ATC run richer. Cold air is denser. Because there's more of it, it makes your ATC run leaner. Because of this phenomenon, it might be tempting to change your idle jet. Don't do it.
Your Honda ATC does have an idle jet. However, it comes from the factory in the correct size. Idle circuits the the only circuits on the ATC that are adjustable. Every other circuit requires you to replace a jet to alter the ratio. The idle circuit simply has a small, slotted brass screw on the side of the carburetor. If you turn it slowly in one direction, the idle will slow. Turn it slowly in the opposite direction and the idle will speed up. Some riders make a mark on the carburetor next to the idle screw indicating where it idles best. This provides a baseline should you make slight adjustments for altitude and temperature.
If It Still Doesn't Idle
If your ATC still won't idle correctly, do not change the idle jet. Chances are it's some other problem. One of the most common problems is that the carburetor has some gum or lacquering in it, affecting it's performance. In this case, it needs to be disassembled and cleaned. It's recommended to use a rebuild kit when you reassemble it. Other problems may include ignition timing. On four-strokes, valve timing may be an issue. These are standard tune-up items.