Dear Ralph:
A thought occurred to me the other day that made me think of you. With all of the latest injection systems, leaner calibrations, cleaner burning oils, stronger-firing ignitions, electronic engine controls, it has started to become more obvious that snowmobilers don’t spend much time (if at all) looking at their spark plugs, let alone changing them.

But anyone who grew up riding sleds knows how much you can learn from reading your spark plugs, and what a critical component they are in consistently strong engine performance.

This is evident when we ride with somebody who hasn’t a clue of where to start looking when their sled “doesn’t run right”. Past the obvious “do you have gas” and “is the intake plugged with snow” the first thing you do is look at the plugs! They don’t know what to be looking for in most cases. Ralph, it is obvious to you and me, but maybe we should be going over some of these things to bring the new guys up to speed?
Rich Everston

Good point there Rich. Today’s sleds run so well that we have seen spark plug failure reduced to only a few times per year, where we used to need to replace plugs on a majority of machines for as long as I can remember. All of the reasons you listed have contributed to plugs being able to operate at an appropriate firing temperature and resist fouling.

With the new four-strokes, the plugs seem to last longer and foul less. Replacement is most often due to flooding choke-equipped models. They, too, will provide the demanding engine tuner with burn temperature and fuel mixture information.

Dear Ralph:
Why is there a “dummy” starter gear (a solid ring instead of a gear) on the backside of a drive clutch on some sleds? Isn’t this just extra rotating mass that slows down the acceleration of the engine?
Chris Caldwell

There have been many instances over the years where an engine has been used in various models, some with electric start and some without. Riders, service techs and factory types started to notice the engines ran smoother and how the clutches lasted longer on the electric start sleds. Part of it was due to the added mass of the starter ring gear to the primary. Some riders even started to install the gear on their clutches, even if their sled didn’t have electric start. Think of it as a “balancing gear”.

That is what you’re seeing in the dummy ring mounted to the backside of the primary. It is now part of the engine design, so the engine runs smoother and in better balance, either with a starter gear or dummy ring of similar rotating mass. Does it slow down the acceleration? Logically yes, but the benefits far outweigh the alternative. Your engine and primary clutch run smoother and last longer because of it.

Dear Ralph:
I own a Polaris XC 700 SP with VES. I’ve read with great interest some of the changes and issues the 800s have been dealing with, specifically with the power valves, but it seems as if the 700s are not mentioned in the same page as the 800s. Is this due to the popularity of the 800s, or is there something about the 700s that make it immune to the issues of the 800s?
Tim Pierce

Most of the power valve durability issues were on 800s; here’s why. Excessive heat is the enemy of the valve itself. Most power valve reliability issues were found on 800s that experienced “marginal cooling”. The 800 is generating more power to begin with, but there is a significant difference in the cylinders themselves between the 700s and 800s. On the 700 cylinders you will find additional coolant passages on the exhaust side that are NOT on the 800s (larger piston uses more real estate). This allows the power valves on the 700s to operate cooler, due to the additional heat removal afforded by the extra cooling capacity.