Dear Ralph:
I own a 2003 Arctic Cat Firecat F7 with 11,156 miles on it. When do you recommend that I do an engine overhaul on this sled? It runs great with excellent fuel mileage and uses very little oil. Since my dealer hasn’t seen a Firecat with such high mileage he is unable to answer this question. I welcome your comments and/or suggestions. I have attached a picture of the odometer.
Tim Segeren
Lakeside, Ontario

If it was me, I would do the top end at a minimum, and right about now would be a good idea. At a minimum inspect the top end and see what the piston skirt clearance and ring end gap is. If the piston-to-cylinder tolerances are getting “sloppy” you can replace the pistons, rings and wrist pins with relative ease compared to the alternative. Left unchecked for too long, a sloppy piston can rock inside the cylinder bore and catch on the ports and the rest of the story gets ugly and expensive.

Maybe the right question here is at what point should a preventative inspection be conducted? I’d love to hear what everyone’s experience is on this one (ralph@snowtechmagazine.com). This will vary from engine to engine, but many two-stroke engine builders will tell you that 11,000 miles on a top end is just plain lucky. Number of seasons can be as much of a factor as total miles, depending on storage conditions and the shape of the engine when it was put away for the summers.

Dear Ralph:
I ordered a new Yamaha Apex GT and it comes standard with the Camoplast Rip Saw track. I recall you had extensive experience with this new track design, and was wondering about top-end speed with this track. I only ride hard packed groomed trails in Northern Ontario. Compared to a 1” track, is there a significant difference in top end speed? I’m going to stud the track with 96 studs, so would there be any significant difference between a 1” track with 96 studs and the Rip Saw with 96 studs? Any detailed information would be greatly appreciated.
Andy Leblanc
Ontario, Canada

The main factors in top end difference between tracks would be weight, wind resistance and rolling resistance. Back when 1.25” lug height tracks first came out there was more of a top end difference as older design 1.25” tracks had fuller lugs, or more of the lugs actually at 1.25” height. The Rip Saw uses the latest track construction technology so it rolls easily, is super-light and doesn’t have the wind resistance of a full-bar lug pattern of previous 1.25” tracks.

When we add studs to the formula, it could be argued a 1” track allows the use of shorter studs, thus less rotating mass, and this will affect top end. Again, you could also stud a Hacksaw or conical lug track and see a slight difference. If maintaining top speed AND having traction devices is paramount for you, one option would be to install one of the Ice Ripper pre-studded tracks that is a Rip Saw with 256 lug studs installed that is said to only weigh about one pound more than your stock track. I doubt you’d have any trouble finding a buyer for the track you’d be taking out!

Dear Ralph:
Can you explain, in simple terms, how the Ski-Doo DPM system with carburetors can be clean enough to be EPA-certified? If this is true, then why is everyone spending so much money developing expensive electronic fuel injection systems that just complicate things?
Ricky Hoffman

The Ski-Doo Digital Performance Management (DPM) found on the 2005 and 2006 PowerTek 800 engine indeed uses carburetors and is fully EPA-certified for 2006 and beyond. A carburetor, by itself, is relatively “stupid” in that it has no inputs to compensate for things like throttle position, air temperature or air pressure. Fuel is fed to the engine by virtue of a pressure differential between the float bowl and the air flow through the carb throat, or venturi. The greater the pressure difference, the more fuel delivered.
Ski-Doo electronically manipulates the float bowl pressure as a means of varying the fuel delivery, allowing them to combine smart electronics with a simple (and stupid) mechanical carburetor.
The previous versions of DPM used inputs to their on-board computer (ECU) such as engine RPM, throttle position, air temperature, engine water temperature and, on Summit models, ambient (barometric) pressure to determine the proper pressure to be applied to the float bowls for proper fueling.
The PowerTek version of DPM adds to this a knock (detonation) sensor, an important element to being able to reduce the fuel delivery far enough to become compliant. Normally, if you reduce the fuel delivery too far a 2-stroke will detonate, and this leads to engine damage if allowed for much more than an instant. The knock sensor allows the fuel delivery to be right on the edge all of the time, that is the edge of detonation and maximum power output! If the engine starts to detonate, even slightly, the sensor picks up the acoustic signature and the ECU (computer) takes the steps to correct the condition immediately. This is accomplished though both fuel delivery and ignition timing, as well as power valve positioning.
Electronic RAVE power valves are another addition to the PowerTEK version of DPM. This is the magic combination to become EPA-compliant with a carbureted 2-stroke; fuel control, ignition control, a knock sensor, and electronic power valves. Logically, any 2-stroke engine with these elements should be able to do the same; like add a knock sensor to a Cat EFI engine that already has electronic power valves and get the mapping right…
Why do it any other way? Only Ski-Doo has this level of control to do so with a carbed 2-stroke, but it shouldn’t be beyond the capabilities of the others. It is viewed as a “stop-gap” measure that should be effective until 2010, when the emissions regulations get even tighter and could render this system non-compliant. We’ll see.

Dear Ralph:
I just wanted to share with your readers some information about Yamaha’s warranty, including their extended warranty. In 2005 I purchased a new Yamaha after owning Ski-Doo for years because my knees won’t let me ride a REV. I love the 4-stroke mill and the entire machine in general, until it comes to the warranty. Did you know that Yamaha dealers in Canada will not perform needed repairs under the Yamaha U.S. warranty if you bought your sled in the U.S. and have a breakdown in Canada? This goes for the first year warranty as well as the Y.E.S. extended warranty. I have had personal experience with the guys I ride with that all of the other three manufacturers honor their warranties in Canada. This can really spoil a long planned trip.

Yamaha told me that I would have to pay to have it repaired out of my own pocket then bring the receipts and parts back to the U.S. to get reimbursed for the repairs. No guarantees though! For a worldwide leader and manufacturer in the industry to refuse warranty because of a border is ridiculous. With the lack of snow in many areas some years, Canada is one of only a handful of locations people can ride; not to mention the trails, scenery and hospitality of our friends to the north make it a great snowmobiling experience. I thought your readers might want to be prepared in case they are planning a trip to Canada. Keep up the good work.
Gary Schoppenhorst
Endeavor, WI

I understand your concern, and this is due to the differences between Yamaha Motor Corporation (U.S.) and Yamaha Motor Canada. It is not a case of same company, different names for each side of the border, they are two very distinct corporations. Why this is a unique situation for Yamaha compared to the other three I do not know, but I have heard of these cases where the owner must pay for the repairs and then submit the receipts for Yamaha U.S. to reimburse them. Fortunately, with the four-stroke engines the number of such claims is quite low. Chances are you’re going to have a credit card with you if you’re from the U.S and riding in Canada, so how big of a deal is it, really? As long as you do get reimbursed in a timely manner, it shouldn’t be. A warranty is not “free service”, it is to make good on parts or workmanship which is deemed inadequate or faulty. Just because a new sled breaks during the warranty period doesn’t mean it is due to a defect.

Dear Ralph:
We were just going through our Polaris 800 twin engines and discovered the power valves were damaged on one. Have you seen this, and is this very common?
Derrick R. – Idaho

Yes, the 800s are known to experience more damage to the power valves as there is not as much coolant in this area as is found on the 700 cylinders.

In response to the extra heat that can exceed the threshold of the aluminum material used to make the valves, Polaris now offers stainless steel valve kits and you can also install titanium ones for even more protection. These materials have even higher melting temperatures, making them better suited to withstand the grueling conditions you mountain guys place your sleds under when doing long, sustained wide-open pulls up a long climb.

Dear Ralph:
Help me understand something; I’m fairly new to the sport, but know a thing or two about motorsports in general. Why can’t I just increase the operating RPM of my sled a couple hundred RPM and go faster? Is each sled set intentionally “low” to provide engine durability?
Randy Nastrould

Your general premise is fairly accurate in that more RPM would provide more MPH, assuming you had the horsepower to do so and all other things were equal (like gearing).
The basic problem here is, when we’re talking two-strokes, is each specific engine and exhaust system combination produces its peak power output across a fairlynarrow RPM range. As long as your changes would allow the engine to operate within this narrow window, you’re going to be correct. However, most sleds are tuned fairly well to allow the engine to operate at its peak power RPM, and they are really not “de-tuned” as you suggest.
We could get into a very long discussion about gearing and clutching, but the key point to take away from this is that every two-stroke has a very specific “target RPM” for maximum power output. Tuners MUST know this number for their specific engine and exhaust combination. Many engine, and just about all exhaust changes or modifications, will change this number, and adjustments to the clutching and possibly gearing will need to be made to compensate.
If your engine makes its power at 8300 RPM, but your clutching and gearing at your elevation only let the engine run at 7800 RPM, you’re missing out big time.
Or, if your sled was originally set to spin at 8000 RPM and you install some go-fast parts so the engine now makes its power peak at 8500 RPM but do nothing to the clutching and gearing to compensate, you’re again missing out big time.
With four-stroke engines, this is really much less of an issue. You still need to know your target operating RPM, but being right on the money is less of issue. Their power bands are typically much wider, and they produce similar power across well over 1,000 RPM in many cases, so if the engine is spinning a few hundred RPM lower than ideal it doesn’t make nearly as much of a difference. Here we could successfully entertain the argument that more RPM will provide more MPH, but HP is going to be the limiting factor. That is, do your have enough power to “pull” the higher speeds? If not, the CVT clutching system will compensate by shifting into a lower ratio, so then what have you gained? Also, as engine RPM rises, CVT transmission efficiency drops, yet another consideration.

Dear Ralph:
The recoil on my Polaris sometimes doesn’t catch when the engine is warm. You have to carefully pull on it slowly and hope it will catch so you can start the stupid thing. Is there anything we can do, or am I at the mercy of the dealer?
Bob B.
Sioux Falls, SD

We checked with Polaris, and they tell us there was a small number of units where this was reported. Inconsistent engagement of the recoil is due to a lack of drag between the friction plate and friction spring that drives the ratchet pawl.

You could remove the exhaust system and the entire recoil unit and take it in as an assembly, then you’re only paying for the internal disassembly and service.