Small Engines (Lawn Mowers, etc.): Stihl chainsaw MS 361 ignition, stihl chainsaw, combustion chamber

Question
Stihl MS361 chainsaw ignition. I understand that the ignition module fires before TDC as there is no advance/retard built into the ignition system. Therefore to avoid back fire, ie ignition firing before TDC and pushing the piston down before TDC, the flywheel needs to spin at about 950 rpm before the plug sparks and those revs carry the piston past TDC as the flame travels through the combustion chamber. Is this true ? If so how can the module sense the flywheel rpm ? Or is it that the voltage from the module is insufficient to strike the spark at the plug until the flywheel rpm reaches about 950 ? If that were so then higher revs would give a stronger ( higher voltage) spark) The kickback is inconvenient and weak with smaller engines but would be an appreciable problem with the MS 361 sized power plant.

Answer
Hello Ross:

Where did you Get the RPM Information from? You can Spin a Flywheel Past the Ign Coil/Module of a Chainsaw, Trimmer or Lawn Mower at 50 RPMs and the Plug will Fire. The Current Output of the Coil/Ign Module Does Not Increase with the Increase in RPMs. The Strength of the Magnets on the Flywheel and the Windings of the Coil/Ign Module Determine the Strength of the Voltage going to the Plug. The Stronger the Magnetic Field Produced by the Magnets on the Flywheel the Stronger the Current from the Coil/Ign Module to the Plug. If a Chain Saw or Trimmer Engine is Kicking Back, then 1- the Flywheel Key is Damaged and is Causing the Plug to Fire Out of Time with the Piston or 2- the Exhaust Port is Restricted. Usually Carbon Deposits Build Up in the Exhaust Port, Muffler or Spark Arrestor Screen (in the Muffler) and Restrict the Exhaust. This Creates More Compression than Normal and Causes Kick Back. Depending on the Amount of Carbon in the Exhaust System, Some Units will Start and Idle but Not Rev Up Due to a Restricted Exhaust. On the Larger Units a Compression Release is Used for Starting Purposes to Reduce the Compression to Make Starting Easier. 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