Backfire???

[Vibe Ray]

What causes a backfire? Is there anyway to stop it? Does it mean something is wrong? My HP usually backfires? Dazzle me with your expertise!!!!

[Richard Martin]

Dazzle us with some symptoms. A backfire is usually caused when a fuel-air mixture builds up in the muffler and then a heat source causes mixture to ignite. A backfire can also be caused by the air-fuel mixture inside the cylinder igniting when the exhaust valve is open. Does it backfire when you shut it off or when you are running the engine?

[65hoss]

Very very common on the kawis. Especially when new. Mine was sounding like a shotgun blast. After all the fuel problems going into the crankcase I shut off all fuel now. I turn the fuel off on the HP and let it run out. This does 2 things. 1st, it allows the motor to cool down before shutoff. 2nd, it doesn't backfire when it finally runs out. I have noticed that by doing this, it has caused the backfiring to stop when I shut it down more quickly.

If you look into the carb when it is shut off, the kawis have fuel sitting in the bottom of the carb.

[AB Lawn Care]

Just like Richard said...any excess gas that has made its way from the cylinder to the exuast.Once the gas hits the red hot muffler it will light up and BANG!Sometimes this is caused by the carb running too rich.It is common on alot of small engines.My 14 kohler backfires ALOT when it is started.....if you don't start it right.Kohler's are well known for that.Now if it is doing it while running you will need to fix it.

[mdb landscaping]

i have the 25 kohler on my lazer. it will back fire if i dont turn it off properly. i asked the dealer, and the best thing to do is idle the machine down and let it sit for a few minutes and then turn it off. maybe the kawis are different, but since then my machine hasnt backfired

[cos]

I back fire too. After eating a couple of tacos at taco bell. I need to sit idle for awhile before I start up.

[65hoss]

With the kawis, it doesn't matter how long you let it sit before shutting it off. They will backfire. As it breaks in more it will stop. But shutting the fuel off and let it stop on its own works great.

[Vibe Ray]

I'm sorry I did not mention that it only happens when I shut it off and it is a 19 HP Kawi. Does that help?

[Vibe Ray]

I'll try out the gas shutoff trick, but doesn't that make it a b*tch to start back up again? And is it completely safe for the engine (no additional wear, etc.)? And why is it more common to new engines???

[Scraper]

Do you idle down before your cut-off the engine or do you shut it off at full rpm? Try letting it idle for 10-15 seconds before you turn it off.

[racerdave]

I have 250 hours on my 20hp Kohler, It will still run on and backfire when shutting down. If I have to shut it down quickly, I will run it rich with the choke then shut it down. works every time, and I have yet to foul the plug.
David

[jeffyr]

My Kohler 20 (160 hours) does the same thing (run on and backfire). I asked the dealer and they said that I should shut it off at 1/4 throttle. He corrected me and said that you should let the 16 kohler idle and cool but not the 20.

I tried it and it's a little better---but doesn't seem right to me to shut in down at 1/4 throttle without idling.

jeffyr:confused:

[Premo Services]

I have the lazer hp and the info about letting it idle a little while before shutting down and this has all but eleminated the backfiring. I have noticed white smoke sometimes when starting the engine,not all the time,wonder what that can be?

[65hoss]

Vibe, no it won't hurt the mower to shut off fuel. Actually, it is recommended you shut off fuel. It is not hard to restart either. Put throttle up a little, pull choke, hit key. Spins over just a second and fires right back up. We do it at every job.

Kawis do this when they are new for some reason. My 14hp did this most of last year until it finally stopped once it got a lot of hours on it. My 12.5hp has finally stopped doing it. Now the 23kawi is finally getting better, but since I kill the fuel, there is nothing to backfire anymore.

[Richard Martin]

Originally posted by Vibe Ray
I'm sorry I did not mention that it only happens when I shut it off and it is a 19 HP Kawi. Does that help?

This is normal on a lot of engines, both single cylinder and twins. I wonder if it has anything to do with the particular blend of gas that is available to a specific area? Some areas of the country, mostly the larger metro areas, get gas that is high in oxygenates and this may be contributing to the problem. But, I digress. All of my engines do this and that would be a Kaw 12.5 single, a Kaw 14 single, a Kaw 17 twin and a Koh 25 if I shut them off right after I get done using them. If I let them idle for a short while (2 minutes or so) before shutting them off they don't do it.

Originally posted by Mow Money
I have noticed white smoke sometimes when starting the engine,not all the time,wonder what that can be?

Sometimes when an engine sits a particular way a little oil can enter the cylinder(s). When you start the engine the oil is burned off. I wouldn't worry about it.

[grassyfras]

whats idle is that a like full run on the throttle i have back fire only when the temps are around 80 and above

[Mowman]

Vibe,
To solve your problem let the engine idle for a few minutes when finished mowing. This should sovle your problem. My 20HP Kolher Command will backfire everytime unless I let it idle and cool down a bit. I'll let it run while I blow off the driveway and then shut it down, thus no more backfire. Give it a try, hope it works for you.
Good Luck,
Mowman

[Chopper Lover]

Good Question, Vibe!

Backfires occur either out the carb, or out the exhaust. Generally, the reason for the backfire is because a valve, either intake or exhaust, is open when the spark plug fires off.

What I think is happening when your motor backfires is as follows:
You shut off the key killing the spark to your cylinders. The next stroke the cylinder makes forces the unburned fuel out into the exhaust system causing it to burn or "explode" (in the muffler or somewhere else in the exhaust system).

Please keep in mind, if your engine starts backfiring at times other than when you shut it off, or if you activate any of the emergency kill switches, you may have engine problems that need to be PROMPTLY addressed.

Turning off the fuel is a good idea, even thought I don't do it, because fuel can occasionaly find a path to the crankcase where it will mix with the oil. When this happens you MUST change the oil before you run the motor again. It is probably a good idea to change the filter also.

Mark

[jeffyr]

Here is a quote from the Walker owners manual for the Kohler 20hp.
"Use fast idle for stopping engine to avoid run-on and backfiring"

which is exactly what my dealer said to do with that motor. Still sounds odd, but it is working.


jeffyr:o

[Jman]

Here I go again on shut-off. If the engine is equipped with a fuel shut-off solenoid (wire or wires going to the carb) shut the engine off wide open throttle NO LOAD. This means deck off and sitting, not moving. These are air cooled engines, do not take the moving air away from the engine by idling them down. This will cool the muffler but will increase the temperature of the engine which is harder on the engine in the long haul. If the engine does have a fuel shut-off solenoid on the carb when shut down at wide open throttle is the same as those of you who shut off the fuel to the engine and let it run out of gas. That will not hurt the engine as well. As the engine shuts down it will not starve for oil, the oil pump still functions, it will not wash the cylinders down with fuel, it is not there to cause that problem. This idea is new to most of us and we need to change with the times. If you had the OLD K series Kohlers, Wisconsins, cast iron Briggs the proper way was to slow the engine down to cool the muffler. We used to call the backfire problem "brown seat syndrome" when I was in a shop, as it always happened just as your leg was coming over the steering wheel on old riders. Hope this helps, if still unclear let me know. One last thing, if all else fails read the ENGINE owners manual. The Kohler manual states if the engine does not have a fuel shutdown solenoid idle the engine 30-60 seconds and then stop engine. If the engine is equipped with the shut down solenoid position the throttle somewhere between half and full throttle. :)

[Vibe Ray]

Guess what guys?! I figured out how to stop it from backfiring! It has nothing to do with being new, I think, What I do is after running it full throttle with the blades engaged I let it cool down at half throttle or a tad bit below for a minute and then kill it at half throttle or a tad bit below as well. Even though it goes against my instincts, it works great! Obviously this engine was designed to cool down and kill at half throttle instead of low throttle. Try it out guys and let me know if it helps!

[GreenQuest Lawn]

After reading these posts a few days ago I started trying different things on my 25hp kohler. what I found is when I load it on the trailor I idle it all the way down, then up (just till the rpm,s rise) then shut it off, hasn't backfired yet

[jdjoe_97]

I have a pair of JD M665's, anoying thing about them is the
backfiring everytime of the 25hp Kohler Commands!! But like all of
you have suggested idling down the motors and letting them cool for just 30 seconds eliminates the backfiring. I still have one that almost always runs backwards a second or two. I haven't talked to the dealer yet about that problem. Also one of the motors puffs a little blue smoke only at start up. Any of you have that type of problem with the kohlers?? Thanks

[Jman]

jdjoe_97 try my suggestion for two days and let me know back. Shut it off with the throttle wide open after letting it run wide open for thirty seconds. If all else fails check your Kohler owners manual. Your engine is equipped with a fuel shut-off solenoid.

[Albemarle Lawn]

Last week when my Kohler 25 backfired loudly. Nice lab was coming up to say hi to me like he always does.

I hope the poor dog doesn't think I'm drawing a bead on him!!!

Ken:rolleyes: