kohler backfire....

[sailinstud420]

Quick question,

after runnin my 23 kohler hard for a while, when i back down on the throttle fast it backfires? Any ideas why?

[NCSERVICE]

Cut the motor off when it is running at full speed or 3/4 throttle. I dont remeber why but if you idle it down and then shut it off it back fires.

[richallseasons]

if i idle mine down and shut it off right away it backfires but if i idle down and give it four or five minutes of cool down no problem,so me and my guys are in the habbit of giving all the engines cool down periods before shut down.

[Restrorob]

Cut the motor off when it is running at full speed or 3/4 throttle. I dont remeber why but if you idle it down and then shut it off it back fires.

Do you shut your truck off that way ? It's best to idle for a couple minutes as richallseasons said.

[LawnBrother]

I know it's a different engine, but I had the same problem on a 15hp Kohler last year. I tried letting it cool down idle for a few minutes before shutting it off and that stopped the backfiring. Not long after the backfires started I ended up replacing a faulty ignition module. Not sure if they are directly related or just coincidence. I have heard of backfiring and ignition modules both being common problems with some Kohler engines.

[iluvscag]

this is what you do, turn it off at idle and write as it shuts down rev it up high. no backfire.

[Trinity Lawn Care, LLC]

We usually make sure that we wait a little bit before we shut it off (after idling down), and more time than not works like a charm.

[lawnspecialties]

Hey, Kohlers are notorious for that. People would duck for cover sometimes when I had to shut mine off in a hurry.:laugh: Just let it idle a little before shutting it down. Longer if it's hot outside or you've been working it pretty hard. Heck, all I run now is Kawasaki liquid cooled's and I even let them idle down before shutting them off to cool them down. Get in the habit of loading the mower and strapping it down, then shut off the motor.

[ed2hess]

Does an air cooled engine actually cool down if you put it in idle or does it cool better when left wide open? I am guess it is better to leave it at full throttle... I don't want an engine to backfire so I shut all Kohlers down at full throttle....

[puppypaws]

I have had two 27 hp Kohlers and they both backfired so I talked with the top engine tech for Chesapeake Engines and he said that Kohler air cooled engines need to be switched off at 3/4 to full throttle so that it would get all the gas and fumes burned out before it shut down. I tried mine at 3/4 throttle and it would still backfire so I started switching it off while it was running wide open and it never back fired again.

[whiteslawnservices]

i HAVE A 32 HP 2006 IT DOES THE SAME THING LET IT IDEL FOR A MINUTE THEN TURN IT OFF IT WONT BACK FIRE THEN BY THE WAY DONT FORGET THE RPMS YOUR RUNNING THEN IDEL IT DOWN COUNT TO 10 THEN TURN IT OFF IT WONT BACK FIRE THEN JOEWHITE

[puppypaws]

Does an air cooled engine actually cool down if you put it in idle or does it cool better when left wide open? I am guess it is better to leave it at full throttle... I don't want an engine to backfire so I shut all Kohlers down at full throttle.... I am sorry I did not see your post first but you are absolutely correct in your way of thinking, the only way a air cooled engine has to lower the temperature is by air movement over the engine so it actually becomes cooler by running faster.

[Brianslawn]

just put the choke on at same time as shut off.

[thecrankshaft]

For engines with a fuel shut down solenoid:

just put the choke on at same time as shut off.

That is definitely not what you want to do.

Do you shut your truck off that way ? It's best to idle for a couple minutes as richallseasons said.

Would it matter if you did shut your truck off like that?

These engines have an oil pump driven off of the crankshaft gear. Even while the engine is spinning down, you'll still have oil pressure (if not pressure, at least flow).

When you turn off the key, the spark is killed. These engines run lean (lean mixture = hot combustion temperatures) which cause the muffler to get very hot. If you shut the engine down at idle, there is enough manifold vacuum to draw fuel out of the idle circuit and pass it through the engine, where it can ignite in the exhaust. Keep in mind that these engines also have a fuel shut down solenoid which stops the flow of fuel to the carburetor venturi when the engine is shut off (however, manifold vacuum at idle will draw fuel out of the idle circuit, again). When you shut the engine off at full throttle, the governor will respond by opening the throttle fully when the engine is spinning down. This creates venturi vacuum, but will not draw it out of the carburetor fuel bowl because the fuel shut down solenoid has blocked the flow.

For engines without a fuel shut down solenoid:

Yes, then you can idle the engine down and shut it off.


If you don't believe me, read the owner's manuals.

And yes, these engines cool better at high speed than at idle. However, the muffler will be cooler at idle than high speed.

[Paradise Landscapes]

I shut mine down after idling for about 3 mins. I haven't had any problem with backfire.

[thecrankshaft]

Why idle it if you don't have to? No need to waste gas.

[lucforce]

"the only way a air cooled engine has to lower the temperature is by air movement over the engine so it actually becomes cooler by running faster."

Less air flow over cooling fins at low rpm-Yes.
Relatively lower temp at idle-Yes.

Generalized Thermodynamic effects: Less fuel burned=Less heat produced.

[Restrorob]

Does an air cooled engine actually cool down if you put it in idle or does it cool better when left wide open? I am guess it is better to leave it at full throttle


you are absolutely correct in your way of thinking, the only way a air cooled engine has to lower the temperature is by air movement over the engine so it actually becomes cooler by running faster.


And yes, these engines cool better at high speed than at idle. However, the muffler will be cooler at idle than high speed.


Have you Guys seen the show Myth-Busters ?
Well I performed my own experiment today.

Test engine; Kohler CV25S Spec. # 69511 Freshly Tuned and Serviced With 828 Hours, Mounted on Sears Garden Tractor With Hood Removed To Simulate Open Cockpit ZTR
Test Equipment; Raytek Raynger ST Non Contact Thermometer
Chepo Walmart Stop Watch

Areas Tested; Center of # 1 & # 2 Valve Covers.
Rear Center of Engine Block.
Center of Muffler.

Test Went as Follows;
Cold Start-Up and Idled 1155 RPM For 30 Minutes.

#1 V.C. 158 Degrees ---#2 V.C. 155 ---Block 192 ---Muffler 480

Engine At Full Throttle 3700 RPM No Load For 30 Minutes.

#1 V.C. 160 ---#2 V.C. 158 ---Block 198 ---Muffler 462

Engine Back At Idle 1155 RPM For 4 Minutes.

#1 V.C. 146---#2 V.C. 142 ---Block 190 ---Muffler 396

The full throttle Temperature most likely would have been a little higher had the engine been under load mowing but I could not perform that test on company time, Then Engine Was Shut Down With No Back-Fire.

I attribute the higher numbers on # 1 valve cover due to the muffler mounted on that side of the tractor just below the valve cover.

Just some food for thought; A higher RPM results in a higher number of detonations in the cylinder per minute with less time to dissipate heat in the cylinder. A lower RPM on the other hand results in a lower number of detonations per minute which would be more time to dissipate heat in the cylinder.

Crankshaft, You are right about the proper shut-down procedure.
Below is out of the owners manual.
Due to the results of this experiment, Myself will continue to idle cool engines as have for 15 yrs. because it works for Me, And everybody else should do what works for them.

[fly-4-fun]

Great job on the test Rob, I've often wondered what the actual temp of an engine was at full and partial throttle.

[NCSERVICE]

For engines with a fuel shut down solenoid:



That is definitely not what you want to do.



Would it matter if you did shut your truck off like that?

These engines have an oil pump driven off of the crankshaft gear. Even while the engine is spinning down, you'll still have oil pressure (if not pressure, at least flow).

When you turn off the key, the spark is killed. These engines run lean (lean mixture = hot combustion temperatures) which cause the muffler to get very hot. If you shut the engine down at idle, there is enough manifold vacuum to draw fuel out of the idle circuit and pass it through the engine, where it can ignite in the exhaust. Keep in mind that these engines also have a fuel shut down solenoid which stops the flow of fuel to the carburetor venturi when the engine is shut off (however, manifold vacuum at idle will draw fuel out of the idle circuit, again). When you shut the engine off at full throttle, the governor will respond by opening the throttle fully when the engine is spinning down. This creates venturi vacuum, but will not draw it out of the carburetor fuel bowl because the fuel shut down solenoid has blocked the flow.

For engines without a fuel shut down solenoid:

Yes, then you can idle the engine down and shut it off.


If you don't believe me, read the owner's manuals.

And yes, these engines cool better at high speed than at idle. However, the muffler will be cooler at idle than high speed.


Thank you! that is the long version... cut off the motor 3/4 throttle no back fire!

[Jman]

I say, with fuel shut off solenoid, wide open. As far as not shutting off a truck that way, does a truck have a governor to limit it to somewhere around 3600 rpm. As far as idling the engine down to cool it down, remember the words "air cooled". Would you take that same $40,000 truck, pull in from a 500 mile trip, jump out and drain half of the antifreeze out of the radiator and let it sit there and idle to cool down??? Just a thought.

[sailinstud420]

wow, thanks for all the insight, I didnt realize what a common issue this is.

Next question, will it do any harm to have it backfire? It is fun to scare the heck out of the nieghbors, they all think something blew up, plus that way you look like you are running old equipment, which means your not making a ton of money, which means you get the sympathy vote!! :drinkup:

[Restrorob]

Next question, will it do any harm to have it backfire? :

A backfire in a older rusty muffler could break loose a internal baffle causing a annoying rattle and the loose baffle could get into a position to restrict exhaust flow output causing higher engine temperatures and poor performance.

[thecrankshaft]

Severe and repeated backfire can shear flywheel keys and blow head gaskets, as well as cause damage to the muffler.