Small Engines (Lawn Mowers, etc.): Troy-Bilt LTX-1842 Lawn Tractor w/18H B&S Engine - Backfires, gas vapors, air mixture

Question
I've had problems with this Troy-Bilt(LTX-1842) lawn mower backfiring for over 3 years now. It has a B&S Intek Single w/Spin-on oil filter and is an 18Horsepower engine. It backfires after it heats up, which is everytime I go to shut the engine off to empty the bagger. It makes a pretty load bang like a gun going off. I just waiting for something to come through the hood. I've changed the sparkplug, gas filter and have also adjusted the fuel/air intake to see if that would do the trick... It still does it, I'm not sure what it is. One kid at a repair shop said it's a bad engine but I think he's made things worse. Please help, thanks!

Answer
Hello Mike:

This is a Pancake Muffler Isn't it? These Mufflers when Mounted on the Larger HP Engines (10hp and up) Tend to Backfire Unless you Allow a 1 to 2 Minute Cool Down Before Shutting Off the Engine. I Removed All My Pancake Mufflers and Piped My Mowers to Use a Cigar Muffler. If the Carburetor has Air Mixture Screws, then Adjust the Main Air Mixture Screw in 1/4 Turn (lean Out the Main Jet). The Problem is Caused by Excess Gas Vapors Trapped in the Muffler and the Compression Release Allow the Engine to Fire Into the Exhaust when Shutting Off the Engine. With the Engine at Idle for 1 or 2 Minutes, the Muffler Clears Itself of the Unburnt Gasses and you will Seldom have the Backfire. Hope this Helps. I am Here if You Require More Assistance. Let Me Know What Happens, Please. Thanks.

Good Luck

Respectfully  

John