Engine RPMs up or down on shutdown?

Discussion in 'Lawn Mowing' started by srheinz, Jun 3, 2010.

  1. srheinz

    srheinz LawnSite Member
    Messages: 13

    I've got some conflicting info recently. One dealer told me to always slow the engine all the way down at idle because it's easier on the engine. Another dealer told me to always shut down at full throttle because when you slow the rpms the engine backfires more and that's hard on the head gasket. I'm no expert on small engines but would really like to know what the truth is.
  2. thomasglenn

    thomasglenn LawnSite Member
    Messages: 15

    I've never really thought about it but I always drop the rpms before killing it. I've turned off alot of engines in my time and have never blown a head gasket.
  3. tmanmi

    tmanmi LawnSite Member
    Messages: 46

    If you have backfire problems you can either let it idle for a minute or so and waste gas or move the throttle just a little off idle and it shouldn't backfire. Never heard of blowing head gaskets with backfire but I did have a grasshopper that blew the muffler out from repeated backfires. Dealer rep told be about shutting down at just off idle, it worked.
  4. mbrew

    mbrew LawnSite Senior Member
    Messages: 491

    Mr. James Varnon, a very fine aircraft engine mechanic and instructor taught me over thirty years ago to idle an engine before shutting it down. The reason is as follows: when an engine is at power it is drawing an awful lot of air through the carburetor and fuel along with it. When you suddenly stop the ignition, there is still quite a bit of fuel on the way to the cylinders which will re-liquefy and wash the oil from the cylinder walls and will eventually get past the rings to contaminate the oil. The amounts aren't huge, but over the life of an engine it can become a factor.

    I have never run any engine that had a written start up and shut down procedure (this includes aircraft and industrial engines), that they didn't want a minute or so idle before shut down. In addition to the reason above, giving a little bit of a gradual cool down is often given as a reason.
  5. Richard Martin

    Richard Martin LawnSite Fanatic
    Messages: 14,699

    I always like to let mine idle for a minute or two before shutting them off. If I shut them off without letting them idle first I get a variety of undesireable results. Sometimes the lifters in my Kohler will tick on restart. Sometimes one of my engines will backfire. Other times I'll get a cloud of smoke out of my Kawasakis.

    MS_SURVEYOR LawnSite Bronze Member
    Messages: 1,002

    I have a 30hp Kohler that has a slight backfire at idle to low rpms. Nothing bad. But when I shut by advice from many, including puppypaws, at 3/4 throttle, I have no backfire. Now my Briggs Vanguard likes to be at idle.


  7. Hoy landscaping

    Hoy landscaping LawnSite Senior Member
    Messages: 836

    mine backfires when its too high and too low. i stick it in the middle and turn the key
  8. turf&tree

    turf&tree LawnSite Member
    Messages: 112

    MBREW is correct, you are washing the cylinder if you shut down at full throttle.
    I get landscapers bringing in equipment all of the time and as soon as they unload it they shut down at full throttle and BANG. I love the business it provides for me. I have another who has all 35 employees mixing 2 stroke at different rates. Wow what they bring me to fix, mostly seized hedge clippers and string trimmers but hey you guys are rich, right?

    MS_SURVEYOR LawnSite Bronze Member
    Messages: 1,002

    Thanks! I'll take that under advisement!

  10. hackitdown

    hackitdown LawnSite Silver Member
    Messages: 2,621

    Don't the factory manuals say idle?

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