The spark plug gives you a "snapshot" of what was going on inside the
engine at the moment (or very shortly before) you shut it off.
In order to know whether you have the correct main jets by reading the
spark plug, you have to ride it wide open throttle for as long as you feel
safe/comfortable... then shut the engine off and coast to a stop. You can't
idle back to the trailer or ride back to the house to pull the plugs.
If you want to know whether you have the needle clip set at the right
height, you have to run it at 1/2 or 3/4 throttle (after you're sure you
have the correct main jets in it) and shut it off... coasting to a stop, and
read the plugs on site.
Looking at the plugs after the thing has lost power and quit running
just tells you that it was running like crap before you shut it off...
unless there is permanent evidence of detonation or perhaps anti-freeze
contamination.
"Clean" pistons come from running the engine rich, however you may be
rich on the main jets and deathly lean on the needle... giving you a hot
spot at perhaps 1/3 or 1/2 throttle.
Another possibility is that you're clutched for the wrong rpm now that
you have a different set of pipes. If you're forcing the engine to run
closer to it's torque peak that what the jetting specs were based on... you
can get extreme piston temperatures, detonation, spark plug overheating, all
sorts of the things.
Keep in mind that if your engine is supposed to be clutched to run at
say 8,500 rpm... then there is really no way that it would ever normally run
at 8,000 and wide open throttle for any length of time. So to run at 8,000
rpm would normally require perhaps 7/8 throttle... letting in less air and
possibly drawing more fuel (more vacuum) than 8,000 rpm at full throttle
does.
Being clutched for the incorrect rpm can lead to all sorts of problems
that you wouldn't normally expect... because these engines are designed and
tuned to work with the clutch to put out extremely large amounts of power
for their size.
Anyway, I would suggest you get the main jets sorted out first, then the
needles (should check 1/2 and 3/4 throttle with dual taper needles) and
finally sort out the idle speed and pilot settings. New plugs help
tremendously when dialing the carbs in, because it's easier to see the
changes.
Good luck,
David
--
Hi, thanks for the replies.
The plugs are definately burnt not fouled. They usually come out of
the machine white/grey. The jets are set to factory FIII specs (I
cant remember what that is now though) according to the dealer.
The temperatures I ride in arent extrememly cold, usually from -10 to
+3 (celcius). The machine has an electic temperature gauge too and it
never runs really hot. When I am riding it stays low but if I stop
and leave it running, the temperature does go up but not even close to
extreme. I would think it was normal.
The mechanic did say that the tops of my pistons were "Cleaned off."
I guess he means down to the aluminum with no carbon left. The
machine was better after getting it back from them with the new jets
and everything tuned up, but it did still ruin the plugs. I can feel
when it starts to happen and a few minutes later the skidoo loses all
its power.
How about oil? I havent been religiously using Bomabardier Brand like
they say you should. If I dont have any oil and I am at a gas station
I just take what they have on the shelf!