November 2015 Ask the Experts

Secondary clutching, power jets, studs, reverse troubleshooting and more!
crossover snowmobile Yamaha FXR
Reader Reactions: Secondary Clutching
Tech Editor, Olav Aaen, discussed the pros and cons to recent OEM changes in secondary clutching (Clutch Situations, p. 58, Jan. 2015). Here’s one reader’s comment and another’s answer: “Sadly, the use of encapsulated straight pressure clutches on 4-strokes is not only inefficient, in my opinion, but adds to the high belt temps on A/C turbo sleds. The new secondary clutch A/C engineered for 2016 is hopefully better since they have been chasing some belt issues on the turbos for the last 4 years. You are 100% correct that a torsional clutch with both side and torsional pressure is much better. If you add a lower angle helix to the mix, the secondary performance becomes efficient and performs better on the big uber 4-strokes.”

Interestingly, Yamaha has used their 40-year-old button torsional clutch on the Apex since day one with no belt or clutch issues. Since 4-strokes do not spin backwards, the only reason to use a non-torsional clutch on a 4-stroke is for accounting, not engineering, reasons. I bet if someone cost-accounted all the warranty costs that have incurred versus the cost of using a torsion clutch from day one on the 4-strokes, the numbers would favor the old design.” – Ed Welsh, New York

Reverse Psychology
Q I have a technical question regarding a 1999 Ski-Doo Formula 380 Deluxe. Reverse always worked great until the other night when I pressure washed the engine compartment. Now when you start the engine, it continuously alternates between reverse and forward. I blew out all plugs at the reverse button and CDI ignition. I’m at a loss and need your help! – Perry Gilbertson

A When power washing the machine, there are a couple of issues that may have occurred. Checking and cleaning all the plug connections is a necessity, but also using dielectric grease in them will help make a true connection. Be sure to disassemble the switch and completely dry it out, along with reconfirming the grounds in the chassis are all in good connection. Lastly, there is a possibility that the actual switch was shorted and will not hold the connection. If so, it’ll need to be replaced.
– Jason Houle, Straightline Performance

Power Jets?
Q I searched for tuning info on a 1994 Mach Z 780 Mikuni flatslides and did not find much. I was surprised to see it had power jets. It is going to be used for asphalt drags. The product description sounds good, but should I keep them? – outlaw fab shop

A They sure do have power jets! I may have some old microfiche to give you stock specs. You can also remove them and run them as a 95-and-up setup. Ski-Doo also has a number 0 jet that is a plug, so you can disable the power jet. If your motor is modified, a good set of bored MZ flatslide carbs works well. – Todd Guthrie, Dyna-tech Performance

Watch it Bounce
Q I got a 2004 Ski-Doo 600 SDI H.O. It hits the rev limiter at 1/2-throttle or more, but if you ease into it, then it doesn’t hit the rev limiter. I rebuilt the top end and I’ve rebuilt the primary clutch. Any ideas? – AJ Truman, via Facebook

A There is a possibility that the new rebuild on the engine is producing more HP than the older and the current clutching is no longer holding the proper rpm anymore. This is a slight possibility, but more than likely, the installation of the clutch parts are incorrect and are now causing the high rpm to hit the rev limiter. – Jason Houle, Straightline Performance

Drop it!
Can the stock rear skid on my 1999 Mach Z 136 be lowered with short shocks rather than strapping down? Is there a kit or idea for this? I’m just starting off with some recreational ice dragging for now. – monstermach99
1999 Ski-Doo Mach Z 136 LT Long Track
Ski-Doo’s 1999 Mach Z 136 was considered an LT model, or “Long Track.” Some of today’s trail riders  prefer 136+ inches.
A Yes, you can shorten the shocks or use shorter shocks. Just compress the suspension to your target height and measure your shock length from bolt to bolt. There are a lot of cheap shock options to use to get it where you want it. – Todd Guthrie, Dyna-tek Performance

ISR Stud Rules
Q I need clarification. It doesn’t say in the rule book how far to the edge of the outside of the track the studs can be, so can I put the backer right to the edge of the track? – machz975

A There is no stud placement rule when it comes to drag racing, only a maximum height over the tallest point of the track. For snocross and some cross-country racing, there are stipulations as to stud location. ISR has the rules posted on their website to double-check your specific need. – Todd Guthrie, Dyna-tek Performance

The Right Ratio
I have an 800 imp. Ski-Doo. What’s the best comp ratio to run for ice and/or grass drags? – ski-doo ps 1000

A Too many things go into determining what is best for your application. Different pipes, porting and ignition timing all have an effect on it, but here is the basic concept: Asphalt and ice guys usually run a lower compression ratio than the dirt guys do. 800 triples can be 14.5 to 16:1 comp ratio for ice and asphalt. The grass guys can be 1 or 2 points tighter than that for grass. Like I said, a lot of things play into a final comp ratio for me to be able to give an exact answer. This is where some guys will put tens of thousands of dollars into a motor to change tuning aspects and find the sweet spot for their particular sled. – Todd Guthrie, Dyna-tek Performance

Wire it Up!
Q I have a 1994 Mach Z 780 for asphalt. Right now I have a stock tach, headlight and taillight. I thinned down the harness of all the other gauges, lights, speedo, etc. I would like to eliminate everything except what’s needed for a VDO Tach, kill, tether and, of course, stock ignition. I can make the harness and weather pack connectors, just need some input or sketch to do so. – outlaw fab shop

A Very easy! Green on your tach to either yellow wire from your stator, then ground the remaining yellow to a good ground. Tach red to a battery power, and tach black to battery ground. The kill switch and tether are just grounding the CDI black when the switch is activated/tether pulled, so one ground wire can be run to both. I never ran a voltage regulator, so I would not worry about one. – oldschool780
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