2005 Ski-Doo Racing Handbook, Page 136Get this manual
SECTION 05ENGINE PREPARATION
Jetting, horsepower, and B.S.F.Cdata can be obtained with dyno testing but also confirmed with field testingThe tried and true method of determining mixture ratio is to inspect the parts of the engine that are directly exposed to the combustion processThe two best indicators are the spark plug and the piston domeThe color and where it is located are the two things to look forChocolate brown on the insulator, ground electrode, and piston dome indicate proper mixtureThe ground electrode should show difference in color just at the radius of the electrodeThe engine must be operated under load for at least one minute to obtain accurate readingsEstablish the C.R.A.Dby using the following formula: 1737,97 C.A.PC.R.A.D= -460C.A.P= Corrected air pressure C.A.P== Barometric pressure readings (in Hg) R.HEVapor pressureS.Px - 100 See saturation pressure (chart 1)S.P= Saturation pressure (in Hg) R.H= Relative humidity () Record the C.R.A.Dwhen correct jetting has been establishedThis is your base line for future useExample: Testing established 400 main jet at C.R.A.Dof 100One week later, the C.R.A.Dat the track is 110Use the following formula to establish the new main jetNew C.R.A.D Baseline main jet Newmain jet Base line C.R.A.D110 400 Example: -100 New main jet440