Dear Ralph:
I have a 2002 Polaris XC 800 SP with a single pipe, high flow intake, (2) flow-rites in the dash, boost bottle, & clutching all of which is SLP. Their products are as advertised. My problem is I’m on my third piston/jug set in three years. It keeps burning down the PTO side while cruising 45-55 mph in temps in the mid to high 20s. Main jets are 620, clip position # 4 from the top.

The damage is always on the exhaust side of the piston and the jug is wiped out instantly. I’ve done the visual checks on the plugs at various rpm ranges & they’re almost black throughout. Snow conditions were good & water temps were fine & I monitor that constantly while cross checking readings with my brother’s same machine. I’m at the end of my tow rope with this jewel and you’re probably it’s last hope of not becoming a very expensive mailbox. Thanks for your help & keep making other mags bird cage liners.
Mike Vranich

OK, so the engine is going down on the PTO cylinder when running in the midrange. It sounds like it is detonating in this area. Detonation can be caused by several things; poor fuel quality, advanced ignition timing, poor or improper fuel delivery or an air leak in the intake tract are the most common.

Now, you mention running a larger main jet (620) for some extra insurance (recommend jetting is a 540 main at 10-40 degrees F). Problem is, increasing the main jet size does very little for the throttle range you’re seizing up at. The larger main jet will overload the engine with fuel when running 3/4 to full throttle. When you back off on the throttle and start cruising, the engine will be overloaded with fuel for a while until it dissipates and runs clean in the leaner jetted midrange area.

Ideally, to add some insurance, put a .020 needle shim washer under the needle e-clip in the number 4 position. This will put the needle in the effective #4.5 position, and this will increase the fuel delivery from 1/8 throttle to 3/4 throttle. Exactly where you are cruising and having seizure problems. You should also drop the main jets back to something closer to what is recommend to make the sled perform well. At a 620 main jet, the sled will be slow because it is always overloaded with fuel when you’re at 3/4 to full throttle.

But before we recommend that you just add fuel to the midrange, you need to verify that everything is correct in that engine. It sounds like you’ve checked the ignition timing both with a timing light as well as with a dial indicator and everything shows correct. If so, and if you are running the proper CDI box for this model, timing should be a non-issue. If you are running the wrong CDI that has high timing in the midrange, it could cause this problem and either changing to the proper CDI or adding some fuel in the midrange via the needle shim should correct it. Running in the regular-fuel switch mode may help as well. This would reduce the timing to provide more engine protection, but the negative to running in the regular switch mode would be a little less horsepower.

Next, you need to make sure the fuel is at least 91 octane non-oxygenated, ideally purchased from high traffic fuel stops to insure it has not lost any octane from sitting in the tank for an extended period of time. If you are buying his fuel in the middle of nowhere, it would be wise to either add some octane booster (NOS racing formula works well) or run in the regular switch mode. If the only fuel available is oxygenated fuel, you should consider dropping the e-clips (raising the needles) to the #5 position (oxygenated fuel runs leaner and requires larger jets) and, then the main jets should be increased by 2 sizes (580 mains).

As far as fuel delivery goes, disassemble the carbs and make sure there is nothing lodged in one of the orifices. The PTO side carb is the one that needs to be cleaned. Make sure to take the needle and seat and the main jet out, inspect and with compressed air blow through those orifices. If something such as a piece of fuel line or other debris was sitting above the needle and seat, it could block fuel flow into the carburetor. This would cause an intermittent lean condition that would be tough to troubleshoot (we have actually run into this type of problem before). Next, the carb and fuel tank vent lines need to be inspected to insure they are venting properly. A pinched or kinked carb vent line would cause this condition as well. A fuel tank vent line kink or blockage could also cause this problem, but it would be less intermittent than what you’re seeing. Also, a fuel tank pickup that was plugged with debris could cause this problem, but it would be a more remote possibility as well.

Finally, air leaks in the intake tract after the carburetor could cause this problem. You state you’ve checked the engine for an air leak with starting fluid and one did not show up. That’s good, we know that for now, there are no leaks. Did you make sure to check it with the engine at full operating temperature? Sometimes air leaks will not show up until the engine reaches its operating temperature. Also, if the base nuts came loose, it could have developed an air leak that you did not know about. The only one who would have known was the guy who disassembled the engine after it went down. In any event, you should be using the metal base gaskets rather than the paper ones. I believe that all 800s built after 2003 had this metal base gasket.

I hope this helps. The needle shim position should take care of the problem unless it is caused by something wrong in the fuel delivery system or an air leak.

Dear Ralph:
I was reading about the new Rotax 800R engine in the last issue, both the dyno run and the info on the 3-D RAVE valves. The way I read this, the 800 R is fitted with “variable valve timing”. Correct?
Peter Norton

I suppose you could make that claim about any of the power valve systems, as the exhaust port timing is varied by the position of the exhaust valve. In the case of the 800R it isn’t a matter of being simply “open” or “closed”, there is the intermediate position allowed by the use of a main valve and the smaller “fingers” controlling the sub ports, independently.

So the 800R’s three-position valve control is closer to what we could call “true” variable valve timing. Some riders think the electronically-controlled valves are capable of infinite positioning, but as far as I know they all operate on an “open” or “closed” basis, none of them utilize an intermediate positioning. Not even the servo-motor configurations. Why not? We’ll find out!

Dear Ralph:
Here’s the deal – I’m wondering if since my sled claims to be “87-octane” safe that I could safely increase the compression and run say 89, 91 or even higher octane fuel and make more power. Sound logic, right?
Max Harpell

This is a fairly safe generalization. Most of the engines, in stock form, that proclaim to be 87-octane safe respond nicely to a set of tighter heads with more compression, producing more power and increasing your fun-factor.

This is even more attractive if you’re running the machine at elevation. As operating elevation increases, you can generally run either a: lower octane fuel or b: more compression. An engine designed for sea-level operation but used exclusively at higher elevations can run more compression on the same octane fuel.

A few words of caution – increasing the compression ratio will tend to reduce the operating RPM, and thus the clutching will need to be adjusted to compensate. Of course, more compression for a given elevation will require higher octane fuel to prevent detonation. And, simply cutting twenty-thousandths off the head isn’t always going to work, you should be using well-designed heads from reputable shops that have taken into consideration the entire head design. Too much compression can also make the engine surge, so make such choices wisely and on the advice of seasoned tuners.

Dear Ralph:
I just looked at a brand new Yamaha Phazer and saw the “open tunnel”. What’s up with that? Wouldn’t this cause one to get a wet butt? Doesn’t make any sense to me.
Hunter K.

The reason the tunnel is open under the seat on the new Phazer models is to keep the exhaust system cool. The snow from the track will cool the exhaust system, much like snow cools an extrusion and the coolant inside.
While there is clearly more snow visible under the seat and on and around the tunnel, there didn’t seem to be much of any difference in the amount of snow that would get all the way up on to the seat. The seat is fairly high, and most of the snow that collects is down on top of the tunnel instead.
It’s kind of funny, some people suggest Yamaha left this open to save weight. The amount of aluminum saved would amount to a small piece of aluminum foil, a couple of ounces at best, so that’s not it. Primarily it is for exhaust cooling, but one has to admit the styling afforded by being so different carries some “weight” as well (no pun intended). It looks different and it is different.

Dear Ralph:
I’ve been out of the sport for the past 15-16 years, as I was living down south for this long. But, as fate has it, I’m back up in Minnesota now for at least the next year or so, and much to my surprise I discovered your column is still an excellent resource for no-nonsense objective snowmobile information.

Forget brand preference, I want some sound advice on what sleds I should be considering. Basic trail riding and the typical usage, nothing fancy or specific. What are your suggestions? I appreciate your insight and opinions.
Respectfully,
Old Timer Back in MN

Maybe we should call you Rip Van Winkle. I’m not sure how familiar you are with the recent changes in technology, but since you’re writing we have to assume you’re not completely in the dark.

While all of the sled makers now offer true turn key reliability, there are some models that stand out as excellent choices for your demographic. Any of the new 4-stroke models would have to be major considerations, as all you do is gas and go, for the most part.

You make no mention of power levels or requirements, so we would have to consider the likes of the Polaris FS, the Arctic Cat 660 4-stroke models, and the Ski-Doo Legend series. All of these are going to have modest power levels, enough to get around but not high-performance by any means.

If you’re an experienced rider, then we can jump up to 120 HP and consider the likes of the Yamaha Vector or the Arctic Cat turbocharged 660s, and on the high end the all-new Jaguar Z1.

Of these models, my gut instinct is the Yamaha Vector would be the closest to your request, but could be more than what you need in terms of power and performance. The Polaris FS is fairly new, and the Legends and Jaguar Z1 are all-new, so there is little in terms of reliability data to go on here. The 660 engines from Arctic Cat are rock-solid, naturally-aspirated and turbocharged. The turbo tends to be on/off at times, so it is more of a performance package than a sit back and relax package.

I’d feel comfortable suggesting any of these to you. Knowing more about you, I could properly qualify you further to best match the machine to your wants and desires.

Dear Ralph:
I want to install a different track into my Ski-Doo Renegade. Currently it has the 16” wide 1.25” lug height track from Ski-Doo. I was considering the Ski-Doo 1.75” track, or one of the Camoplast 1.5” options. I ride mostly in the U.P. of Michigan, so you know the variety of snow conditions we can run into from hard pack to all-out deep powder. Thanks!
Dan Nelson

Two options come to the top – the Ripsaw 1.5 and the Intense 1.5. The Ripsaw will be better on hard packed trails, the Intense will be better off trail, specifically as the snow gets deeper and will be better out west. You state 70-30 on trail / off trail, this is a usage percentage, how do you rate importance of each usage? Go Ripsaw 1.5 if the 70 trail is more important than the 30 off trail……and if the trails are hard packed. Soft packed trails and the Intense will likely be equal, and then better as the snow increases. Flip a coin for what kind of snow we’ll have this year……it likely comes down to a crap shoot. The Intense will be more aggressive in straight line, like running more studs, where the Ripsaw will allow some cornering stability. Either will likely require more carbide or better skis to balance it out front and rear. 70-30 I say Ripsaw, 50-50 I say Intense.

I would not suggest the 1.75″ 16-wide track for the U.P., I don’t think it will live on the hardpack IMO. Lugs this tall tend to get somewhat squirrely on hardpack, so it isn’t really a good trail track. We pulled one of these off a 600 SDI Renegade two years ago and installed a Ripsaw 1.25, which was a much better choice for the U.P. at that time. The two 1.5s above are as tall as I dare go for any length of time on hardpack.