Why Does My Yamaha Motorcycle Carburetor Have Two Wires Going into It?

Carbs have evolved a lot over the years, and are still nipping at the fuel injector's heels.

Carburetors have been around for good long while, and for most of that time automotive futurists have been predicting its inevitable demise. But it hasn't happened yet, and it probably isn't going to happen any time soon -- a fact that arises from a sort of hybridization between mechanical fuel mixers and the electronic engine controls that make modern fuel-injected bikes so livable, versatile and efficient.

Throttle Position Sensor

This is something that you're likely to find on any Yamaha, Honda or Suzuki, even carbureted ones. These manufacturers have been using simple computers for many years to control spark advances and to supply the ignition control module with information that it needs to determine how you're using the bike. Optimal ignition timing changes depending upon the load on the engine, engine rpm, temperature and throttle position.

Electric Choke

Your Yamaha may or may not have an electric choke, and it's pretty easy to tell if it does. A TPS sensor will typically mount on the throttle shaft, opposite the throttle linkage, but always on an axis with it. The electric choke mechanism will mount either at the very top of the carb next to the airbox, or at the very bottom, depending on the type of carb on your Yamaha.

The TORS System

Many Yamahas utilize a throttle over-ride system called TORS. The TORS system was initially designed for bikes using a twist throttle, and it keeps the throttle from sticking at wide-open if something goes wrong in the assembly. The TORS unit is a very large, metal box that hangs off the carb where the throttle cable would normally screw in; instead of going directly into the carb, the throttle cable goes through the TORS unit. The two wires in question don't actually go into the carb, but into the top of the TORS.

Carburetor Heater

Ever noticed that warm gasoline has a stronger smell than cold gasoline? Fuel's volatility -- its ability to dissociate at a molecular level -- increases with temperature. Ice-cold fuel doesn't want to fully vaporize and burn in the engine, which is why many road-going and off-road bikes use carburetor heater. The electric carb heating element gets the fuel up to a more reasonable temperature to increase engine efficiency and power for those willing to brave the elements and ride regardless.

References

• The Essential Guide to Motorcycle Maintenance: Tips and Techniques to Keep Your Motorcycle in Top Condition; Mark Zimmerman
• Haynes Motorcycle Basics Techbook; Haynes Publishers
• How to Repair Your Motorcycle; Charles Everitt
• Engine Management: Advanced Tuning; Greg Banish