Small Engines (Lawn Mowers, etc.): snowmobile, screw driver, olymic

Question
hello John, ihave a 1971 ski doo olymic that seems to be overheating.  i lose high rpms ahfter an hour or so of running, and aquire some pre ignition when i go to turn it off.  is my analyisis correct?  if so what can i do to correct this.  plugs, fuel mix, and fan are all operational and working correctly.  the sled runs fine, just seems to get alittle hot. thank you, jamie

Answer
Hello Jamie:

You May be Correct or the Exhaust Port May be Restricted or there May be Carbon on the Piston Top that is Heating Up and Causing the Pre-Ignition. 1- Did you Check the Exhaust Port and Muffler? The Following is a Basic Instruction File for Doing a Diagnostic on the Engine for this Problem. Any Input is Appreciated. **Remove the Muffler and Make Sure the Exhaust Port is Clear. Rotate the Engine Until you can See the Top of the Piston and Make Sure there is No Carbon Built Up on the Piston Top. If there is Carbon on the Piston Top, then Use a Flat Screw Driver and Carefully Remove the Carbon from the Piston. If it is, then Try to Start the engine with the Muffler Off. If it Starts and Runs Properly, then Clean the Spark Arrestor Screen in the Muffler or Replace the Muffler if Required. 2- What is the Compression when Cold and when Hot? You can View a Breakdown/IPL at this Site Addy; http://www.skidooparts.com/ and Select Online Parts Finder at the Left of Page. If you Hit a Snag or this Does Not Correct the Problem,  I am Here if You Require More Assistance. Hope this Helps. Let me Know What Happens, Please. Have a Happy Holiday Season and May the All Mighty Bless You and Yours. Be Safe and Happy. Thanks.

Good Luck

Respectfully

John

PS: I am Allowed to Answer 10 Questions a Day. If you See I am Maxxed Out, then Try Submitting your Question at or Just After 8pm EST (US). My New Day Starts then. Comments and Ratings are Greatly Appreciated. Thanks.

Respectfully

John