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Tech Tip: Plug Tuning / Plug Chops

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Plug Tuning

This is not my writing, but useful information when tuning your ATV.

A plug chop is a very useful method of taking a look at the combustion efficiency resultant of the fuel/air mixture. High RPM's is NOT what this is about. It is air / fuel flow. At nearly any RPM above idle.

To perform a plug chop on the Grizz (or any other automatic), is a bit more tricky than a standard tranny, but the idea is the same.

The objective, is to run the warmed engine at WOT (wide open throttle) for a short time and kill the engine and stop its movement quickly. Then pull the plug and inspect it's color.

Shutting off the ignition is easy, but "stopping" the engine's rotation is more difficult because the engine braking will continue to drag the engine even after you kill it.

My solution to this problem, is to do the plug chop run on an uphill grade. Not neccesarily a steep grade, just enough. Once you are ready to 'CHOP" the airflow, hit the kill switch, and brake hard to get it stopped ASAP. Dirt will help a lot with this as your traction will improve as you brake against an uphill slope.

If you could stop it "INSTANTLY" from a WOT run, the plug chop would be most accurate.

Rules of the game:
The plug chop should be done ONLY with a "CLEAN" air filter and a new or at least very clean spark PLUG. If you alter the airflow (new pipe, new filter, etc...) after the jetting proceedure is painstakingly done, expect to start over again from the begining, without passing "GO". Meaning, make all the changes you expect to do "BEFORE" starting this.

Lean can cause expensive damage. DON'T run lean. Period.
Rich can waste some power and stink, but will not cause damage.
Rich is better than lean. DON'T run lean. Period.

Did I mention, don't run lean?

I warm up the engine with the old plug, then switch over to a new plug.

After you have the machine stopped (in a safe place), get your plug wrench out of your tool pouch and remove the plug. Look at it's color.

White = Lean. DON'T run lean. Period.
TAN(-) = Slightly lean ..."@ the throttle level chopped at". (WOT, 1/2, etc...)
TAN = good mixture ..."@ the throttle level chopped at". (WOT, 1/2, etc...)
TAN(+) = slightly rich ..."@ the throttle level chopped at". (WOT, 1/2, etc...)
Black = Way rich, may or may not stink and/or perform poorly.

...TAN2 is about the color of a paper grocery bag. Just about right.

The exact colors will vary depending upon several factors, including local fuel quality, humidity, temperature, etc...

All the above should be performed several times for an accurate average.
All the above should be performed for 3 different throttle levels, WOT, 3/4, 1/2)
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Good info there. I'll be doing some tuning/chops this weekend.
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