Service and Tuning Notes From the September 2005 Issue of SnowTech:

600 SDI Program Update
Does your Ski-Doo 600 SDI foul spark plugs during warm-up? Or, does it surge excessively when the pipe is cold during acceleration? Ski-Doo has made available a revised ECM program for those 2004 600 SDI models and 2005 MX Z 600 SDI Renegade models that exhibit these symptoms (other 2005 600 SDIs are not affected). The new calibration is said to reduce the possibility of plug fouling, provide more consistent performance at higher elevations, better maintain a consistent pipe temperature to reduce “cold pipe” surging, and to reduce backfiring when you cut the throttle. We’re told that only those machines which exhibit these symptoms should have the update installed.

Revised RX-1 Mountain Specs
Owners of 2003 and 2004 Yamaha RX Mountain sleds are encouraged to update their machines to the 2005 model specifications. Applying the 2005 model specs to the 2003 and 2004 models will minimize shift RPM loss at higher altitudes and provide better overall performance. Basically, the sled will run at the proper RPM more consistently, thus providing improved performance over the original 2003 and 2004 specifications. This suggestion comes straight from Yamaha as a way to enhance the high-altitude operation of these models. You can obtain these specifications from your local Yamaha dealer, or find them in any specification source for the 2005 model.

2005 Liberty 900 Updates
Maybe you own a 2005 Polaris 900, or maybe you’re considering buying a carryover at a great price. Either way, Polaris has made many detail upgrades that have been implemented on the 2005 build.

A small number of units were affected by a drive shaft upgrade. A small number of units were also in need of new fuel line clips, and a small number were in need of a new foam seal around the headlight. The ECU programming was also enhanced to improve cold starting. These updates should have been performed during the season.

Since then, all of the 900s should have already received additional updates to reduce engine vibration, improve performance, fuel economy and drive belt durability. This includes installation of new motor mounts and a newer ECU program. Owners of these units would be wise to verify all applicable updates have been performed on units in their possession to ensure best possible performance and reliability.

T-660 Turbo Torque Arms
Black Magic Racing did some looking into the '04 and '05 Arctic Cat 660 ST models and found that these sleds are not immune to engine movement. They put the sled up on a stand and in a word, "HOLY"! You wouldn't think that a motor that big would even need to be bolted down! (That was a joke). Oh yea, she moves.

They got a good feel of how the motor was moving; just like any other sled, up and back, basically trying to twist itself out of the chassis. This, as you may already know, really screws with the efficiency of the clutches, is hard on belts, and hard on the mounts and everything else that is attached.

They fashioned up a torque arm, installed it where they believed it would be the most effective, and engine movement was nearly eliminated.

In a nutshell, the T-660 4-strokes are no different than the 2-strokes. They move around, and this affects drive belt alignment, offset and center distance. Translation, we can do a better job at maintaining clutch-to-clutch distances and power transfer consistency. If you want or need a torque arm for a 660 Arctic Cat 4-stroke, Black Magic has them (218-681-1150 or www.blackmagicracing.com). Order part number #70-1471 for $59.95. Power is useless if you can’t get it from the engine to the track!

REV Hesitations and Erratic Performance
One thing we continue to experience each year with many sleds, particularly the Ski-Doo REV models, is where the machine will begin to run erratically, to the point of maybe even missing and backfiring. You clearly know there is something not quite right with the running quality.

This is often caused by poor contact between the spark plug wires and the spark plug terminals. This area is an electrical weak-spot in the ignition system integrity, as there will be a collection of black residue that eventually acts as an insulator, as well as arcing that deteriorates the spark plug end terminal. This is one reason the harder metals used on the solid-plug end are preferable to the softer aluminum ends on plugs with screw-on ends (cheaper).

OK, so your sled isn’t running right, and it seems like an ignition problem. You carefully remove the plug caps, noticing how far down on the plug they were, as caps are often not fully seated and this too can lead to the continuity issues. On the REVs, you need to lift the caps with extra caution, as we’ve seen these easily damaged if you yank on the wire instead of the cap itself. Notice the plug ends as they’re exposed; ideally there should be some jelly-like material, dielectric jell, on them that could be dried up by now, as well as an abundance of the black electrical residue. Clean all of this crap off of the spark plug if you’re going to re-use it. (Dielectric jell can be bought at most any snowmobile dealer or auto parts store. It is a conductive medium that isolates components from vibration and reduces the amount of arcing that occurs in press-fit connections like a spark plug cap to terminal.)

If you’re doing this out on the trail, it is better to have them clean and dry than leave the old dried up dielectirc jell on there. Often, simply replacing the plugs will remedy the immediate situation, but ideally you want to clean out the inside of the caps, the plug ends, and re-apply dielectric jell. If the plug end terminal is deeply arced and contact with the plug cap connector is questionable, replace it.

We’ve been blowing the crap out of the plug caps with the air gun hooked up to the compressor, and have even sprayed WD-40 up in there to clean it all out, blown it dry and the applied the dielectric jell when you put the caps back onto the plug terminals.

What kind of mileage will one begin to see this? Seems like anything over 1500 miles it starts to be an issue. Many times it is the first thing one actually does to a REV other than add gas and oil (past keeping an eye on the track tension, hyfax, wear bars, drive belt and greasing the suspension).

You also want to pay special attention to the EXACT routing of each spark plug wire. They should not ride on or come in contact with ANY metal part of the engine, as this will provide a ground return path for the ignition to take. This can be a gradual thing, where the plug wire will start to arc to the metal part it is in contact with. You’ll even see witness marks on the wire and the metal where the arcing has occurred.

This pretty much applies to all of the two-strokes, and seems to be more frequent on the REV models, but we’ve also dealt with it on Polaris 800s. If your REV starts to miss and run funny, this is first place you should check. The Firecats are particularly susceptible to the plug caps not being fully seated on the plug. If you’re using plugs with the screw-on aluminum terminals, make sure they are screwed on tight as they can cause similar problems as mentioned above when they come loose and the electrical path sees a higher path of resistance, with intermittent contact occurring.

Smaller Pilot Jets in 4-Strokes
So when old gas gums up the carbs on your sled, what jets are most often affected? Usually it is the pilot jets; the sled doesn’t want to run very well at just above idle or at idle unless the choke is applied is a typical symptom at fall start-up.

Typically, it is the smaller passages of the pilot jets that plug up with corrosion and crap first. Problem is, the carbureted four-strokes from Yamaha all have even smaller pilot jets than what we’ve all been used to dealing with on two-strokes, and now as some of this population ages the sleds are starting to see fuel and carb related problems. For example, the RX-1 is fitted with #17.5 pilot jets! We’re talking small metering orifices here.

Moral of the story; be aware of the smaller pilots in the carbed 4-strokes, and their increased susceptibility to blockage due to fuel quality and storage issues. We continue to see exceptional success with the goofy little Fitch Fuel Catalysts that we drop into every gas can and fuel tank we have, from mowers and ATVs to weed wackers and snow blowers to every single gas can in the shop. We simply do not have any more fuel related problems.

At a minimum, the fuel should be stabilized with a liquid fuel stabilizer and the engine should be run long enough for the treated fuel to for-sure enter the carbs before storage, but even this process is not as fail-safe as in the past due to the constantly changing fuel formulas.

Carb Inlet Filters
If you’re working on a carbed Ski-Doo and are experiencing fuel flow issues, do not forget about the little fuel filters right in the inlet where the fuel hose attaches to the carb! Ski-Doo removed these from the ZX models starting in 2000, so they’re in most everything pre-2000 and some non-ZX models after 2000. These little filters can and do get restricted, and too many shops forget about them.

Tail Light Malfunction
So your tail light doesn’t work and you’ve already checked the bulb; it’s O.K. Now what?

Plan on removing the seat and doing some detective work. The wiring that runs under the seat to your taillight lives a tortured existence down under your butt, taking abuse from the seat action and movement, as well as vibrational friction in the tight quarters. Many times you will find an open in the wiring, or a short to the tunnel that is thwarting the efforts of the lighting system. Often there is a connector under the seat, so you can unplug the tail light and do some continuity checks with an ohmmeter (multi-meter). On the supply side you can easily perform a voltage check on the open connector to troubleshoot the problem. Remember, you need both a supply voltage and a ground return path for the circuit to be complete and for the bulb to illuminate properly.

Water Temp Effects on Tuning
Old school tuners are sometimes thrown a curve ball when a sled with a newer ignition system is causing the performance to be reduced. Often it goes like this; a tuner is having difficulty reaching their desired peak operating RPM, and concentrates on the clutching and gearing variables. They will often notice the machine runs real strong when cold, but performance drops off noticeably when it gets heat soaked.

While you may always notice a slight difference between cold and hot performance, many times it is by design the ignition system and on-board electronics are making a programmed decision. Water temperature is an input used by all modern sled ignition and fuel delivery systems, and as this temperature rises past predetermined temperatures, things like ignition timing and fuel delivery are adjusted to compensate for the engine temp. Bottom line, when this happens you will on occasion notice it. Discriminating tuners will notice it most, and if they’re not aware of how the exact system on their sled works (is programmed) they may waste time worrying about problems that don’t really exist.

Common is a Polaris RMK with mods that runs flat on a particular day. It doesn’t want to pull full RPM, and just isn’t as good as it should be. You have to be able to discern if the water temp is actually high, or if there is a detection (sensor) problem. Most often it is an actual high coolant condition, caused by a host of variables, normally inadequate cooling by the extrusion system for the given snow conditions. Different types of snow/ice provide different heat exchange rates, and heavy pulling conditions as often seen in mountain riding can bring the water temp to one of the many levels of compensation that today’s “smart” machines have.

Each make and model employs a different set of instructions the on-board computer is analyzing to make its adjustments; with the newer injection systems, the complexity of the systems increases. While it provides improved engine reliability and performance consistency, it is nice to know what is actually happening when it isn’t running as good as it could be.

Another classic is on a sled with an airbox temp sensor that is supposed to measure the temperature of the air flowing through the airbox. You run the sled hard for a while, then stop and park for a few minutes. The heat of the engine compartment heat soaks the airbox and temp sensor. You go to take off and the sled acts very lean when trying to start it. Why? The sensor told the computer the air was very warm, so less fuel was delivered at start up. As soon as some air started to flow past the sensor, this condition was corrected and away we go.

Flap Up/Flap Down?
All of the Yamaha four-strokes, three and four cylinder up through 2005, have a heavy rubber flap that covers the engine. Many riders have found it is beneficial to flip the flap up away from the engine as riding temperatures increase.

Why is it in there? To help retain engine heat in extreme conditions. This is why it makes perfect sense that it isn’t needed when riding in warmer temps. We tend to leave it up unless we’re getting closer to zero degrees (F), so if you want a number then use 10 degrees as a general up-down toggle. Try it both ways some day and see what (if anything) happens to the running quality on that day. As it gets warmer out, you will notice more of a change (with it up) and then again as it gets colder (with it down).

1000 SDI Piston & Cylinder Matching
The new type “995” engine, or more commonly known as the Rotax 1000 SDI, may use two different piston sizes. Each cylinder and pistons is identified with either an “A” or a “B” designation. This identifier is found on top of the piston crown, and off to the side of the exhaust port on each of the cylinders. A cylinder block may use two different sizes of pistons, and you MUST match piston “A” with cylinder “A” and piston “B” with cylinder “B”.

When a cylinder needs to be replaced, the cylinder block comes as an assembly with two pistons if you order the cylinder block from Ski-Doo. Even if only one cylinder is damaged, you replace all of them together.