Fuel Screw or Air Screw?

Tuners are often confused when it comes to being able to identify whether a particular adjusting screw on a carb is a fuel screw (that adjusts low speed fuel delivery) or an air screw (that adjusts low speed air delivery). Carb accessory guru Lonn Peterson at Thunder Products tells us that generally, if the adjustment screw is on the engine side of the carb slide it is a fuel screw and thus can be used to fine tune low speed fuel delivery. If the adjustment screw is on the airbox side of the carb, then it is (generally) an air screw and is used to fine tune the low speed air delivery. On most carbs found on late model sleds, this seems to be fairly consistent.

This is helpful to know, as (generally) turning an airscrew out adds more air (a leaner mixture) and turning a fuel screw out adds more fuel (richer mixture). Knowing which is which and what happens when you crank it this way or that aids in off-throttle performance (as the engine comes off idle) and low speed operation, as well as idle stability. Many riders use this adjustment to maintain a crisp throttle response, especially as riding conditions (elevation, temperature, barometer) vary.

 

“Investing In the Future” Kudos

The response to our “Investing in the Future” editorial which encouraged readers to become active in the clubs and associations where they ride, regardless of whether they can perform the physical part of club trail work, was positive and encouraging.

Some clubs responded by stating they need help mostly in the form of physical labor, but this task lies more with the locals than it does the visitors. Some areas actually pay laborers to perform the trail work, as the amount of volunteer labor isn’t sufficient to do all the work, but funds are available to pay to have it done. Our point was that if each one of us gives in some form, there should be an increase in the resources available to each of the clubs that help clear and groom the trails. This is also the result of trail permits in each state; more money is generated to fund the trail maintenance.

One of the more interesting responses came from Al Oatmen, treasurer of the Wayland Snowmobile Club south of Grand Rapids, Michigan. Oatmen basically stated loud sleds were right near the top of the list of things that causes their trails to be in jeopardy of closing year after year, and that if people want to support the clubs and associations (as we suggested) they should not be riding loud sleds.

 

4-Stroke Snowmobile Clutching

One of the nuances of the 4-stroke motors now found in some of the newer snowmobiles is the affect of engine compression braking when you let off the throttle. Owners of the 4-strokes, and those who have spent any amount of time riding one, can confirm this tendency, where the engine helps to slow the vehicle down through the clutching and compression braking that occurs as the clutches downshift the transmission to a lower ratio, much like using a lower gear to slow your car or truck instead of relying solely on the brakes. 4-stroke riders should also be familiar with how the sled coasts once the primary is completely disengaged.

A number of snowmobile clutch tuners have also commented on the conventional wisdom when it comes to using a CVT transmission on 4-stroke snowmobiles. With their broad powerbands, the need to maintain engine RPM within a relatively narrow bandwidth is no longer needed. Some have gone as far as to suggest the primary clutch spring isn’t nearly as important as we’ve always given it credit for.

Then we received an e-mail in regards to the Yamaha RX-1 that stated, “The engine brake affect that pushes the rider forward as it decelerates can be over come by changing the front clutch spring. I put in a very light spring in the drive clutch that eliminates this, from Lennon’s Power Equipment (518-773-7175). This did not in any way affect the ride in any other way. Hopefully this will help other riders.”

 

Arctic Cat Seat Ice Build Up

Many of us have experienced a build-up of ice underneath and around the rear of the seats on the Arctic Cat Sabercat and Firecat models. Curiously, this doesn’t seem to be an issue on M-Series and Crossfire models, so what’s the difference?

Ralph Krick of Fleetwood, PA offered the following observation and insight, as well as his fix for the problem;

“I took delivery of a Sabercat 700 LX in November of 2003 and had the ice build-up under and around the seat on my very first ride. I complained to the dealer and he said other people were having the problem and they didn’t know where it was coming from.

I was pretty sure I knew where it was coming from, and I confirmed this by removing the seat. The heat exchanger is set up into the tunnel and pop riveted. It is sealed around the tunnel with silicone sealer, and I was convinced the seal was not water tight.

I proved this by taking a garden hose and spraying up into the tunnel, and sure enough, it leaked around the heat exchanger. This was where the water was coming from that was accumulating under the rear of the seat. The warm heat exchanger was melting the snow, and some of the water was getting past this seal and re-freezing as it ran out underneath the seat.

I went back to my dealer and told him this, so we put more silicone around the heat exchanger in an attempt to seal it up better. We even laid a piece of wax paper on top of it so when we put the seat back on it wasn’t glued to the tunnel, and then removed it when the silicone cured. (Ideally, let the silicone cure before installing the seat.)

Viola, no more ice and water coming from under the seat. It has not leaked like this again in 3,000+ miles.”

 

Ski-Doo Offers Racing Kit for MX Z 550X

Bombardier Recreational Products, Inc. [BRP] made a significant advance in entry level-snowmobile racing last season with the move of Ski-Doo fan-cooled models to the revolutionary REV platform, and two accessory kits that upgraded the sleds for competition.

With the introduction of the 2006 MX Z Fan 550X model, the company is kicking entry-level racing up another notch. With its REV platform, SC-4 rear suspension, and driveline nearly identical to the new 2006 MX Z 440 racer, the MX Z Fan 550X is a formidable sled.

Add the new 550X Racing Kit upgrade package (P/N 860 429 100) and you’ve got a sled that is completely race-ready. The kit has three major upgrades: upgraded shocks, upgraded clutching and stronger rear suspension wheels, along with bits and pieces to install the package. Some racers will also want to switch to the 1.25-inch track (P/N 504 152 483) for extra holeshot traction.

In terms of shocks, the kit includes C-36 Racing-Clicker Aluminum Take-Apart racing shocks on the rear suspension – the same shocks as on the 440 – and HPG Aluminum Take-Apart piggyback shocks in the front. All shocks are calibrated for snocross racing, but for lighter riders.

A collection of clutch springs, clutch weights and new belt improve acceleration, holeshots and backshifting.

The kit is available now at Ski-Doo dealers, with a MSRP of $1479.97 USD/ 1749.97$ CDN.

 

Polaris and Erlandson Performance Inc. Partner to Develop Performance Clutch Kits

Polaris has announced a development partnership with leading clutch system manufacturer Erlandson Performance Inc. (EPI) of Baxter, MN. Erlandson, a household name in the industry whose clutch components are known for unparalleled quality, superior performance and durability, has been developing performance clutch kits for a quarter century.

“In our eyes, EPI is the clear leader in performance clutches and these kits prove that,” said Ryan Lindell, Pure Polaris Accessories Developer. “The performance enhancements these kits provide our sleds completely exceeded our expectations and we think our customers will feel the same.”

Designed for 2006 Polaris snowmobiles, the new Polaris / EPI kits are engineered to provide aggressive acceleration on the low end, resulting in dramatically enhanced performance on the top end – either on or off the trail.

“All of us at EPI are thrilled to be working with a company like Polaris,” said Glenn & Diane Erlandson, owner of EPI. “In the end, the real winners are Polaris riders because the kit takes an already great performing sled and makes it even better.”

Set for release in October, 2005, the performance clutch kits carry a retail price of $279.99 US / $374.99 CN and will be available for a variety of models including the 2006 600 HO Fusion & Switch back, 700 Fusion and 900 Fusion & Switchback. Part Numbers are found below. 2006 FS Classic, FST Classic & Switchback kits will be available at a later date.

#2875866 – 2006 600 HO Fusion & Switchback
#2875867 – 2006 700 Fusion
#2875868 – 2005 & 2006 900 Fusion & Switchback

For more information and to order, see your local Polaris dealer.

 

Arctic Cat 3 & 4-Year Warranties

Arctic Cat is currently offering special incentives to buyers of brand-new 2006 snowmobiles; liquid-cooled sled purchases between September 1 and November 1 qualified for a 4-year warranty, and liquid-cooled sleds sold between November 1 and the end the year qualify for a 3-year warranty! This consists of the standard 12-month manufacturer warranty, and 24 (or 36-month) extended service contract that mirrors the manufacturer’s warranty. Fan-cooled models also qualified for an extended warranty, for up to three years, and all warranties are said to be transferable.

 

No “Sled Of The Year”?

Dear Ralph:
I realize this isn’t your normal tech question, but I didn’t know who else to ask, so here goes. I notice how other sled magazines (none of which I subscribe to any longer, you should know) like to award a “Sled of the Year” to a brand-new machine each year. My question is actually multiple; first, why doesn’t SnowTech name a “Sled of the Year” or anything similar (because I and many others would place greater value on your opinion) and second, how can the other mags do this before the snow even flies?
Call me “Curious George”

Your second question actually answers the first one. We’ve learned over the years that what the magazines ride in the Spring is often a far cry from the actual production sleds that show up in the dealerships in the Fall. History has demonstrated the machines (prototypes and pre-production units) available for spring photography are just that; photo sleds that “look” good but may or may not be an accurate performance representative of the for-real production sleds. Often, they are hand-tuned (and super-tuned) machines that look very much like we can buy in the Fall, but often are ringers in that they are not a fair gauge from which to proclaim such “winners”.

Long-time subscribers of SnowTech are familiar with how we used to review the test sleds available to us in March in our April issue, but again, history has shown us that to make such bold statements based on a handful of super-tuned prototypes is risky and sometimes downright scary. Most of us can sort through new sleds that have been introduced over the years and identify which ones were dead-nuts right on and those that were dogs right out of the gate, despite glowing reports of their performance in prototype form.

That being said, the mags can pretty much identify what machines hold great potential, and this is the basis (I assume) the choices are being made. Our approach is that we’d rather wait and see how a brand-new model performs in actual production form in the hands of thousands of riders across the snowbelt, and after we get a chance to ride them and tinker with them for an entire season. This approach has proven to be far more accurate in terms of sorting out fact from fiction.

Know this; ALL of the sled reviews you are reading in the Fall before the snow flies are based on the prototypes and pre-production units from January and March. This is true with ALL of the sled mags, but very few come right out and alert you of this. We do. Most of the time this riding of the prototypes is the majority of the riding the magazines do (not us), so they may not know the difference between a super-tuned prototype and the reality of what people like you have bought and are riding. Reader beware. The only exceptions to this would be the late release models (or early release, depending on how we look at it) like the 2006 Arctic Cat Crossfire that came out in January.

OK, so maybe we should declare a sled of the year at the end of the year, or midway through? Designations like this are usually made to help sell sleds, so while the timing is off, we have considered it. Based on our testing last season and feedback from our network of readers and dealers in the field, we would lean towards the MX Z Renegade X 600 H.O. SDI as our “Sled of the Year” from the 2005 models. This could be expanded to any of the 600 H.O. SDI models, as it was an EPA-compliant 2-stroke with exceptional running quality, fuel economy, and overall performance and owner satisfaction. With features like RER electronic reverse, optional 1+1 seating, the REV rider-forward ergonomics, ability to carry cargo and an extra fuel tank (together), and the technologically advanced fuel injection system (already in its second year for 2005) it was the best sled from the broadest perspective, based on real-world production-sled performance and function. Ride, handling, responsiveness, balance, traction, all of it. Especially after we added a Summit windshield and a Ripsaw track.

 

Hood up on F7 – Vent Hose Collapses

Dear Ralph:
With the hood up on any of the F7s I’ve looked at, if you crack the throttle the accordion dryer vent hose on the airbox collapses some. How can this be good for performance?

Don Lastrem

Tell me, how often do you ride your sled with the hood up? That expansion joint tube between the intake up in the hood and the airbox down in the belly pan has the flex feature so you can open the hood. When the hood is closed, that tube is not expanded and it doesn’t collapse. Take the tube off at the top, let it collapse just like the hood is closed, then try to compress it like what you saw with the hood up. When the tube is collapsed, the weaker expansion joints are now horizontal and the tube is actually quite strong. This isn’t a problem. The only thing we know to work on this intake is installing a larger inlet snorkel on the airbox if other mods are being made (exhaust, porting, cylinders). On a stock sled, don’t bother.

Also, when the sled is running there is some pressurization of the intake occurring with it out in front of the windshield up on the nose of the sled. Adding any sort of underhood intake undermines the benefit of the cold air (pressurized) intake and tuned tract length. Cat did a good job with the volume and length of the design, most everyone has come full circle with this one. Dyno operators are learning this is an important factor they sometimes don’t replicate when testing, as this intake design needs the airflow over the hood to replicate real-world conditions and airflow volumes. Just because a sled does something with the hood up doesn’t equate to what it will do out in the field. One must replicate, as much as possible, the field conditions. The closer one gets, the more accurate the data acquisition. All static tests are just that; static. What we’re more concerned and interested with how it works on the snow, in real world usage.

 

General Jetting Advice For Stock Snowmobiles

Dear Ralph:
I’ve got a 1999 Yamaha SX 600. It’s a pretty good sled, but I suspect (based on what the plugs look like) that it is jetted richer than it needs to be. It is bone-stock, except for the track, skis, and transfer rods. With gas prices looking like they’re going to be higher, improved fuel economy would be great.

What can you offer in terms of general jetting advice on stock sleds?

Phil Oveson

We ideally want to look at each model individually, as some engines are known to be more over fueled than others. From a general standpoint, most sleds come from the factory with carb jetting that is going to provide reliable operation. This means the calibration is generally going to be capable of providing enough fuel on a very cold day at very low elevation for a long pull. Generally. On fuel that isn’t maybe the highest of octane, either. Thus, anytime you operate in less than ideal conditions, chances are there’s some extra fuel being used.

A big deal? Sometimes it is, often not. Some engines are designed to operate well across a wide range of conditions and fuel amounts, so they’re not as “finicky” when it comes to needed spot-on jetting to run well. Most of the Yamaha 2-strokes of late and many of the Rotax engines typically fit this description.

Other engines that are “squeezed” for even more performance can become more demanding in this respect, 440 race engines for example.

What one needs to do is first determine what the stock jetting spec is calibrated for. Most of the stock sleds are going to be low elevation and down to –20. With your triple 600 Yamaha, I know from experience that at our 1500 foot elevation and cold temps we ran smaller main jets and dropped the needle, but we would often run richer jetting in December and January (colder temps) then switch to leaner jetting for the rest of the season (warmer). Just watch your plugs.

Usually, most any sled can tolerate a one size smaller main and a half-position drop of the needle (using shims). Some bigger triples can take several sizes in mains, each model is different. This is why reading the plugs, analyzing the amount of wash on the pistons, monitoring exhaust gas temperatures give you the information so you can make informed decisions on what action, if any, can be considered.