backfiring

[Guest]

When it's hot, my 7117h backfires after I turn it off . Is this bad for the engine? I was wondering if the octane rating of the gas I used was too low.(86) Also should I buy Simplicity brand hydraulic oil for the drive train or will another brand due? A co-worker suggested hydraulic jack oil.

[Al]

Hi, The backfiring, techinically afterfire, aka brown seat syndrome is not harmful to the engine. It happens when the engine has been running at relatively high speed and the muffler is red hot inside. You then shut off the key and the engine turns over several times taking in fuel with no spark to ignite it. This unburned gas goes into the muffler and the hot metal inside ignites it. Bang. Worst possible damage: If the muffler is old and thin blows out. The newer engines have solenoids in the carb. that shut the gas off to the main jet when the ignition is cut. This their only purpose. Since these are connected to the main jet, they are sometimes ineffective on slow speed shutdowns. Ex. The new 25 hp Legacy will afterfire unless it is shut off above 2800 rpm. This way the engine is drawing enough air for the gas to come from the main jet. The engine turns over several times with no gas and no combustion, this cools the inside of the muffler and by the time it slows down and gets fuel from the low speed jet the muffler is cooled enough to not cause the problem. The only thing you can do is to idle your tractor down for about 30 seconds before shuting it off. This should help a lot. The Simplicity oil is what they recommend. I would use it. They recommend other oils for various other hydros, from 10w-30, type F ATF, Dextron, 20w-50 etc., depending on the tractor and what type of hydro it has. THis is what they recommend for yours, so that is what I would use. Good luck, Al