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 donâ€™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 hasnâ€™t a clue of where to start looking when their sled â€œdoesnâ€™t run rightâ€. Past the obvious â€œdo you have gasâ€ and â€œis the intake plugged with snowâ€ the first thing you do is look at the plugs! They donâ€™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?
Good point there Rich. Todayâ€™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.
Most of the time, the first sign of spark plug trouble on a two-stroke is a lack of good contact between the connector up in the plug cap and the terminal on the spark plug. Also, wire routing can still cause misfiring; the spark plug wires should not be allowed to rest or touch any metal from the coil to the spark plug; this can provide an intermittent ground path, resulting in misfiring. Often you can see visible witness marks of arcing on the outside of the wire and on the metal if this happens.
The terminal on top of the plug shouldnâ€™t be loose; cheap replacement plugs have soft aluminum screw-on terminals, avoid these. Spend a little more and get solid-terminal plugs, and only use resistor plugs. Non-resistor plugs emit RF interference, which can interfere with the digital ignition systems.
Inspect the white porcelain part of the plug between the terminal and the metal lower portion, looking for paths of electrical travel, stains on the porcelain or arc tracks.
What Rich is really talking about when he says â€œread the plugsâ€ is how the spark plug firing end appears. How dry or wet it is, the color, and the overall condition and appearance. They should be fairly dry and brown, not wet and black.
Even if all is well, the firing end will slowly deteriorate and replacement of the plug will again provide consistent performance.
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.