Small Engines (Lawn Mowers, etc.): CCR2000 Backfire after a few minutes, expansion rings, assembly drawings

Question
QUESTION: I have a 1993 Toro CCR2000 model 38180, serial no. 3909332  It runs for about 5 minutes and then start to backfire, slow down and then stop.   Restarting when warm backfires and off.  If left for a few hours works again for 5 minutes or so then backfires. I have cleaned the carburetor, added a new needle and whatever it is seat in done by the local shop, added a new magneto module.  Any thoughts?

ANSWER: Hello John:

>>From your Description it Sounds like the Rings May Require Replacing or they have Frozen/Stuck to the Piston. If the Rings are Not Flexing/Expanding with the Engine Block, you have the Problem you Described.
>>This is Common in 2 Cycle Engines when a Ring has Frozen/Stuck to the Piston or have Worn Out. >>Try Adding a Small Amount of Marvel Mystery Oil to the Fuel Mix. Approximately 2oz to 1gal of Fuel Mix. If the Rings are Frozen/Stuck to the Piston, Usually the Marvel Mystery Oil will Loosen/Free the Rings and the Backfiring will Stop because the Rings can Flex/Expand with the Engine Cylinder Expansion.
>>Rings must Expand Outward with the Engine Block Expansion in Order to keep Compression.
>>You can View a Breakdown/IPL of the Mower at this Site Addy, https://lookup3.toro.com/partdex/default.cfm and Select Start Parts Viewer. Now Enter the Model Numbers (38180) and Click Search. Now Select View Assembly Drawings for your Year Model.
>>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. May the All Mighty Bless You and Yours. Be Safe and Happy. Thanks.

Good Luck

Respectfully

John

PS: I am Allowed to Answer 5 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


---------- FOLLOW-UP ----------

QUESTION: I waited all summer to install the new rings.  It snowed last night so now really motivated to fix it.  Just finished adding two new rings, honing the cylinder and cleaning all the carbon out. The cylinder was scored in one location and rings worn at same spot.  Once done it started on the first pull and seemed to have better compression.  But again after about 5 minutes of running it started to pop and backfire.  Any new thoughts?  I've thought it could be in the spark plug wire or a gasket that might leak when the block gets warm.
John

Answer
Hello Again John:

>>Did you Check the Ring End Gap before Installing the New Ring Set?
>>What was the Ring End Gap?
>>Is the Spark Plug Firing Correctly when this Occurs?
>>When was the Fuel Filter Changed Last?
>>I'll Research this some more Today and Follow Up to you this PM with the Results.
>>Thanks for the Update.

Respectfully

John