1996 yamaha smart carbs amp gyt kits

There we were at 10,000 feet. We'd just dropped off the edge of Lulu Pass and were winding our way around the backside of the mountain to come up Daisy Pass. The new Mikuni computerized carburetor, dubbed the "Smart Carb" by Yamaha, electronically compensated for all changes in elevation from our 7,000 foot starting point on up to the 10,000 foot elevation outside Cooke City, Montana. Smooth and efficient. Responsive and ready power was always a mere tap of the throttle away with the prototype Yamaha engine setup.

This was a Yamaha-promoted tour of the Cooke City area that was designed to give us hands-on experience with the new deep powder setup that will come as standard equipment on the 1996 Vmax ST series. The "Smart Carb" is just one piece of the performance upgrade. The other is a freer flowing exhaust that gives the Vmax 600 up to five more horsepower than a stock 1995 version.

We'd already seen the new exhaust, at least the version slated for sale as a GYT kit. (Pronounced "git," GYT stands for Genuine Yamaha Technology.) This kit consists of a new two-into-one exhaust pipe, new low windscreen, decals, and clutch and carb tuning tips to cover a variety of uses and use areas. Since the kit can be useful in deep powder as well as on drag strips, there isn't a single "right" setup for a GYT-kitted sled.

One of the keys with the kit is to have the motor pulling at around 8000 rpm, not the stock power setting of 7650 to 7850 rpm. As we (and Yamaha) discovered during our American Snowmobiler Shoot-Out, the right specs make all the difference. Due to a typographical error, the on-site Yamaha technician who converted the shoot-out Vmax 600 from a box stocker to a GYT-kitted stocker had the wrong specs for rpm and nearly went crazy trying to get a performance gain from the new pipe and clutching recommendations. However, thanks to persistence on shoot-out partner DynoTech's part and Yamaha's part, we were able to resolve the seemingly incongruous lack of performance.

Yamaha was quite concerned that what they had sent us for the shoot-out appeared to not work. We were mystified as well. In our experience, of all the snowmobile companies, Yamaha leaves the least amount of anything to chance. Sometimes that works against sales. The apparent lack of performance was of enough concern for Yamaha to fly an engineer from Minnesota to DynoTech's dyno room in upstate New York. With the correct specifications, the mystery was easily solved and the horsepower that Yamaha said was available from the pipe was readily apparent.

When Yamaha sent a technician to the DynoTech dyno, we suspected that this pipe was destined for more than aftermarket bolt-on usage. Good guess. At our mountain test site, it was obvious that a free flowing GYT-type pipe was intended to be used across the board on 1996 Vmax 600s. In addition to the pipe, the new computerized Smart Carb was to complement the free flowing exhaust and maximize the Vmax 600's deep snow ability.

As we go to press, there are four different interpretations of carburetting a snowmobile for mountain riding. You can physically change jets at varying elevations. You can choose electronic fuel injection, which is not available for all models. You can opt for a sled equipped with a high altitude compensation carburetor, such as the HAC system available on the Ski-Doo Summit series or Polaris' new Altitude Compensating Carburetor System (ACCS) found on late-season, limited build Indy XLT SKS models. Or, starting next season, you can set your throttle thumb to controlling a computerized smart carburetor, which appears to be a combination of EFI and mechanical carb setups.

We found the Smart Carb to be rather ingenious. It requires no more electrical "juice" than that which powers Yamaha's electric gas gauge. If your spark plugs fire, so will the smart carb's computer chip. Worst case, if the chip dies, the carburetor has a default mode that will let you limp home easier than you could with a dead EFI system.

The smart carb is based on Mikuni's flat slide TM series of carburetors. The normal 38mm flat slide carb is good. The smart carb is better. What we like is that the new carb retains a lot of the features of a standard carb. You can easily change jets. The throttle pull is light. But, best of all, the computer memory creates a "map" of performance which compensates as you reach higher and higher elevations. Yes, you will need to make clutch and gear changes, but once you've done that, you can ride virtually anywhere without re-jetting the Smart Carb.

The carb's internal computerized program responds to engine rpm and throttle positioning, barometric pressure, the ambient temperature in the carburetor airbox, and the engine's coolant temperature. The micro processing procedure adjusts every 20 milliseconds for every 30 feet of elevation deviation and every one degree Fahrenheit of deviant temperature. Should something go wrong, the program defaults to a "fail safe" mode that sets the carburetor for 1,200 feet of barometric pressure, 25 degrees Fahrenheit for ambient temperature and 122 degrees Fahrenheit for engine coolant temperature. To assist a Yamaha dealer in correcting a malfunction, a diagnostic light on the instrument panel will flash a coded sequence to indicate a specific failure in the processing modes.
The Smart Carb is designed to operate off the engine's supplied current. In fact, we noticed that once you ripped at the recoil cord and pulled the engine over, there was enough "juice" to operate the carb's microprocessors and actually make starting easier. Yamaha doesn't claim this to be a main point of the system, but it is a real world advantage…especially at altitudes where sleds can get very finicky due to lack of oxygen.

In addition to the simplicity, the Smart Carb, unlike EFI systems, doesn't require the heft or extra cost of a battery. Simple. Light in weight. Effective. That about sums up the Smart Carb. Except for the fact that the carb is equipped with an external switch that allows you to compensate for the new reformulated or "winter" grades of gasoline mandated by the Federal government in certain areas of the country. This switch effectively biases the computer map to run about five percent richer to compensate for the lower quality fuel.

Riding prototype Vmax 600s equipped with the Smart Carb and free flowing exhaust left us with these impressions:

There is a noticeable performance increase in hill climbing and straight line acceleration runs when comparing a Smart Carb Vmax against a dumb carburetted model. The Smart Carb setup definitely handled low speed maneuvering in and around tree-studded hillsides better. There was no question that the Smart Carb was more responsive. But attribute that to the better overall cross flow breathing from the improved carb setup and the high flow exhaust.

In test runs against 1995 model stock Vmax 600s, the Smart Carb setup clearly out-accelerated and out-performed the old setup. Of course, with a horsepower gain of 3 to 5 horsepower, you should expect an improvement. It exists.

While the Smart Carb is destined to be used in the long track, powder versions of the Vmax 600s for next season, we could see advantages to having the Smart Carb available on "flatland" Vmaxs as well. But, don't expect to retrofit the new carb to your older Vmax. The engine fittings to accommodate the new carburetor are unique to the 1996 600 twin. It's cheaper to buy a new Vmax than try to retrofit an older Vmax 600. We asked.

In addition to smart carbs and free flowing exhausts, look for a long travel "XT" suspension to be offered in selected models of the Vmax 600 and Vmax 500. The new XT suspension is said to offer over 10 inches of travel. Although we know that Yamaha showed a great deal of interest in the M-10 suspension and that the company did a great deal of testing of the FAST, Inc. suspension in Vmax chassis, the new Yamaha design is based on the existing Pro-Action system. Hence its name, Pro-Action Plus.

Yamaha claims that the Pro-Action Plus (PAP) rear suspension offers long travel with handling. You'll find dual KYB independent floating piston shocks on this unit. These lightweight aluminum shocks are completely rebuildable. The front shock stands more upright to take better advantage of the shock's piston travel.

To reduce friction in the suspension action, Yamaha opted for bearings in key pivot points.

Yamaha will readily admit that the new long travel suspension is not as fast as the standard Pro-Action unit. The extended travel suspension will appear in an "XT" sports version of the Vmax 600 and Vmax 500. At press time shock and spring settings were still to be determined. The final calibrations will be based on test data gathered in Alaska, Minnesota, Montana and Japan.

At this point, other than Tim Bender's one-off Formula One racing sled, we don't hear of any deviation by Yamaha away from its Telescopic Strut Suspension. However, while we agree with Yamaha that the TSS design has some excellent points in sport snowmobiling, we won't be totally surprised to see an automotive style front end on a totally new 440-ish entry.

As for now, a long travel rear suspension, computer literate carburetor and free flow exhaust are good places to start.