Yamaha used Smart Carbs in the 1999s on its 600cc twin snowmobiles like the Mountain Max 600. They were designed to exceed the limits of regular mechanical carburetors to maximize the sled’s performance. Smart Carbs could compensate for the changes in external conditions, so they didn’t require rejetting on mountain rides.
What is a Smart Carb on a Snowmobile?
The main idea behind the revolutionary Smart Carb was to automatically compensate for changes in altitude and temperature. To this end, this electronically adjusted carburetor featured two solenoids that were controlled by a computer chip for precise air/fuel metering.
It was a game-changing feature as rejetting the carburetors for different altitudes is always a headache. Thanks to their unique design, the Smart Carbs allowed the snowmobile to always run nicely regardless of environmental conditions.
At first glance, it looks like an EFI system, but these systems are different. Smart Carbs are self-adjusting carburetors, while EFI is a fuel injection system. Although they are designed for the same purpose, the EFI featured a more complex design.
But unfortunately, Smart Carbs never really became successful, so Yamaha finally dropped the idea and switched back to regular carbs.
They are commonly used on dirt bikes but also appear on snow bikes as well!
Yamaha Smart Carb Issues
Compared to their regular mechanical brothers, the Smart Carbs on Yamaha twin engines were more prone to failure, which caused many headaches. While the majority of these carbs worked without any issues, a few of them were real lemons.
Defective Smart Carbs often caused rough idling, lower top ends and even a stalled engine.
However, it’s good to know that most of the 600 twin engines that featured Smart Carbs also utilized the TORS safety system. In most cases, these malfunctions were caused by the TORS and not the carb itself!
Fortunately, in case of a computer chip/sensor malfunction, Smart Carbs offered a “limp mode” so you could carefully ride the sled home. Sure, a Smart Carb issue ruined the day, but it was still better than an EFI malfunction, which often ended in towing the sled home.
Adjusting a Yamaha Smart Carb
When it came to adjusting a Yamaha Smart Carb, many owners were shocked that the carb only featured one single screw. Yes, it surprisingly didn’t have an air screw, as the system automatically controlled the airflow. The only screw on a Smart Carb was the throttle stop screw (or idle screw), which could be used to adjust the idle RPM. Besides these, there was no other adjustment option on the carb.
Smart Carbs on Yamaha snowmobiles automatically regulated the fuel flow based on the elevation and the external temperature. They appeared on Yamaha 600 twin engines in the ‘90s.
Despite its simplicity, Smart Carbs did a much better job than their standard mechanical counterparts.
These engines were really convenient as mountain riders didn’t have to rejet their carbs based on the elevation. Because of this, these carburetors were often referred to as “jetless snowmobile carburetors” as well.
But unfortunately, some of these carbs came with factory defects, which caused many headaches for the owners and the dealers.
Finally, Yamaha’s Smart Carbs never became truly successful, so the manufacturer dropped the idea after a couple of years of production.