krrii

I have a toro Z master with a 23 hp kohler motor. I starts and runs fine. When I idle it down and shut it off, when the motor is hot, it does not shut down cleanly it wants to keep running then knocks a couple of times and seems to try to run backwards before it stops. If I idle it down and let it run for a several minutes it shuts down fine. This does not seem normal to me. Should this concern me and if so what could be causing it ? Thanks

MrChooks

Hi & welcome to TSF.

What you are describing is usually the result of some fuel still being in the cylinder head and something hot (red & glowing) being present to "fire" it. This is usually carbon build up on the plugs or in the head or on or around the valves.

It isn't good that your engine does this when you shut down - it's not catastrophic - but not good for the engine because the fuel / air in the engine is being fired at the wrong part of the cycle - so should be fixed.

It can also be caused by wrong and / or dirty plugs. So I would change those 1st and replace with manufacturers recommended plug with the correct gap set.

If that doesn't fix your "run on problem" then if you are comfortable with taking off the heads and cleaning it and tidying up the valves - that would be my next suggestion

Basementgeek

Also may want to pull the cover and clean out the grass. A too hot engine will contribute to this also.

BG

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MrChooks

BG is right - whilst I haven't run across clogged head breathing as a problem for "run on issues" - it is a great way to set fire to your engine (often after you have put it to bed in your garage ) so make sure that those airways are clear - a solid squirt of compressed air, if you have a compressor, will do it - else - lift the cowl and brush it all out

krrii

Thanks for the replies. I will change the plugs they probaly need it anyway. Hopefully that will work. If not I will probaly consult someone on pulling the heads. Thanks Ken

MrChooks

No probs - happy to help - if the plugs are old - I would be fairly confident that replacing then with new "correct spec" plugs will fix your run on problem

Good luck with it

SABL

I'm a little late on this one....OOPS!!

I didn't notice any mention of the number of hours on your mower. I also have a Toro "Z" and the meter is on the left fender next to the seat (my unit is 4yrs old w/226 hrs...kinda babied). With the Kohler engine I would guess our mowers are identical. For the price you can't go wrong.... HEAVY DUTY!! Three of my sons have done lawn maintenance for over 8yrs (NOT cumulative) and they were happy with my choice..... I did not consult them prior to my purchase.

MrChooks and BG have given you some sound advice but I would like to add another factor that I did not see mentioned and ask a few questions. Is your Manual choke set properly?? Is the choke plate fully opened when the choke lever is in the down position?? If not, fuel is being sucked into the engine and will cause the symptom you describe with the shut down problem. I think we all have to agree that with any internal combustion engine carbon deposits will eventually form on the spark plug/s, valves and in the combustion chamber of the head. The deposit of carbon on the spark plug/s is the most common and easiest to remedy. Unless you have a high number of hours on your engine, or it has been running unusually rich, I would forego pulling the heads at this time..... I don't think your mower is that old.

How is your air filter?? A dirty air filter is almost the same as running the engine with the choke applied. A good "blow out" with compressed air can make the filter last for years and will help maintain the performance of your engine.... compressors are cheap if you do a little checking. I picked up a nice compressor at Sears (complete with hose and attachments) for under $100. The tank is 3gal and compressor is oil lubricated.... it is superior to the diaphram type and should last for years. An air compressor can be handy around the house.... inflating tires, cleaning equipment, etc.

OK, after all the mentioned info..... bottom line is: check the choke and air filter. Make sure the engine is clear of debris. Change the plug and I think you will do fine.

Let us know,
SABL

krrii

The mower has 565 hrs. I have changed the plugs and both air filters and it is running great. The plugs where in fairly good shape but I believe they were old. The filters were dirty. I checked the choke and it looks to be working right. Thanks for all the help.

MrChooks

Well done indeed - now its back to mowing

SABL

A little routine maintenance works wonders. Glad to hear all is well again.
Stop back any time.

Back to mowing??? I haven'y mowed my lawn for 4yrs....hehehe
My sons do that....I have only put about 2-3 hrs on my mower playing around in my "wildlife" area.....2 acres or so.

K-B

Do not idle the engine down to shut it off. Always shut it off at mid-speed or higher.

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SABL

Hi KB,

Never heard of doing a shutdown at anything above a low idle.... I might have to actually READ the owner's manual on that one. Is there a reason for shutting down at mid or high speed?? I may be wrong but I do not like the thought of "flooding" the cylinder with unburned fuel which can wash down the cylinder walls and possibly contaminate the crankcase oil.

K-B

That is exactly what was happening. Shutting the engine down at idle was causing fuel to flood the engine and contaminating the oil. Kohler pounded that into us the last few Technical sessions, but equipment MFG's are refusing to advise their customers of it.

I have a bulletin about it somewhere, I'll see if I can find it and post more details.

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MrChooks

Guys - I would be really interested in this also -

I was always taught to run air cooled engines at idle for a little while after working it, before shutting down, so that the built up heat had a chance to dissipate. But if the makers are now saying shut down @ 1/2 throttle - I will just have to break with my old ways

The air cooled Lycoming IO 360 in my Piper aircraft most certainly requires a period of idle after flight - although aircraft engines are shut down with the mixture control - thereby starving the engine of fuel - so I guess there isn't any in the combustion chambers at shutdown

SABL

I can see some merit in shutting down the engine at higher RPMs if shutdown is achieved through turning off the fuel valve and not with the ignition switch...but then you must remember to turn off the ignition lest you run the battery down. Of course I am talking about larger engines....perhaps Kohler is making their recommendation with the smaller engines??....or is it with all engines. Like I said, I don't know but will see what happens if this is what they recommend.

Thanks KB ......keep us informed

SABL

I found this at Kohler:


Why does my engine backfire when I shut it off?

Your owner’s manual has proper shutdown procedures to avoid this occurrence. If your engine is equipped with a fuel shut-off solenoid, be certain to set the throttle between half and full throttle before turning the key switch "off."

Still kinda hazy but sheds some light on the matter.

SABL

OK, I found better info directly from Kohler. KB was correct with his info but only for certain engines. It is best that the owner read and follow his manual for the proper operation of the model he/she owns.

Again, Thanks to KB for the info.....for many of us, any kind of information only increases our knowledge.

Thanks to Chooks also, I can tell he has used a wrench or two.

K-B

That sounds right. Nearly all modern rider engines come equipped with fuel solenoids, and EFI engines are found mostly on high-end commercial equipment.

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MrChooks

Yes that sounds right - as the "fuel solenoid" would starve the engine for fuel hence shutting it down with no fuel left in the combustion chamber - similar to the Lycoming shut down procedure