# Kohler CV16S Backfire Issue



## fireflyer141 (Nov 22, 2017)

2002 Craftsman L1000 with the Kohler 16.5 hp engine, has been the best mower ever, until now. I was mowing recently when it started backfiring like crazy. Loud as a gunshot. Tried a different, not new plug, with no change. Gradually got worse and wont start at all now, even with starting fluid. Seems like a weak spark. Any help tracking this down would be appreciated!!! I am a new follower of the forum, Thanks!!!


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## sixbales (May 18, 2011)

Howdy fireflyer, welcome to the tractor forum.

You may have a blown head gasket. Also, you are supposed to periodically clean the carbon off the head. Pull the head, clean it up, and install a new head gasket. Not a big job.

Another possibility is a partially sheared flywheel key. This throws the timing off, can cause backfiring. And eventually timing gets off enough to the point that it will not run.


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## jhngardner367 (Apr 5, 2011)

The Kphler Command series uses a steel flywheel key,....however I would agree with Sixbales that it more than likely blew a head gasket.
Another possibility,is loose pushrod adjustment.


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## fireflyer141 (Nov 22, 2017)

Thanks, I’ll pull it off soon and repost the results. Thanks!!!


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## Bill Kapaun (May 8, 2007)

I would expect you would be getting excssive smoke if a head gasket.
Some of the Kohler powered tractors of this era had multiple ( 1-3) Operator presence Relays.
A poor connection could be causing the kill wire to get grounded erratically
.
Provide the Sears 917.xxxxxx number so one can look at the CORRECT schematic out of the more than 200 craftsman schematics.
It MIGHT make troubleshooting simple.

Think along the lines of an erratic seat switch.


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## jhngardner367 (Apr 5, 2011)

Not always....I have one,here, that never smoked a bit,when it blew a head gasket.
Also, the switch would simply kill it,not cause it to backfire,unless it were repeatedly shorting/connecting .


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## Bill Kapaun (May 8, 2007)

"Also, the switch would simply kill it,not cause it to backfire,unless it were repeatedly shorting/connecting"

Exactly my point!
Some of these have a relay powered by the seat switch that completes the ground for the PTO OR grounds the kill wire. A bad connection and engine vibration could possibly cause this. Temporarily removing THAT relay would eliminate the no/bad spark cause IF that is it.
Makes a lot more sense to check for that than immediately pull a head gasket to look.


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## fireflyer141 (Nov 22, 2017)

Bill Kapaun said:


> I would expect you would be getting excssive smoke if a head gasket.
> Some of the Kohler powered tractors of this era had multiple ( 1-3) Operator presence Relays.
> A poor connection could be causing the kill wire to get grounded erratically
> .
> ...


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## fireflyer141 (Nov 22, 2017)

Checked the keyway, it’s good. Reading the replies it seems that a relay is cycling quickly when the key is in the run position. There are 3 relays there. I switched them 1 by 1 with no change. Reset the coil gap just in case and ran out of light. I’ll get back on it tomorrow. Thanks for the leads!!!


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## Bill Kapaun (May 8, 2007)

IF you don't have an Owners Manual-
http://www.managemyhome.com/mmh/lis_pdf/OWNM/98120014.pdf

The schematic is on page 33/60.
OPR 1 Kills the spark if power is removed from pins 85 & 86.
OPR 2 shorts the stator leads to act as a "stator brake"....
OPR 3 disconnects the Voltage Regulator output from "the system".
So, you could simply remove all 3 for testing purposes.

However, if you have a flaky connection on the key switch OR seat switch OR related connections to them, you can have an increasingly intermittent (until completely open) connection.
A "marginally adjusted" seat switch could also be a culprit. Maybe it finally got enough "slop".....

I think you get the idea. Check the free stuff first.

A BASIC thing I forgot to mention is to make sure the coil kill wire hasn't rubbed through the insulation somewhere and is grounding.To really verify, you have to remove the shroud and disconnect it from the coil.

Also, "some" Kohlers had a "Smart Spark" system that IIRC, required a 12V feed. This ISN't shown on the schematic, since it's "engine". You might check the engine connectors. I "think" that system has purple? wires??
Also check the connection to the carb fuel solenoid while you're down there. It's basically a relay too.
With all 3 relays disconnected (and carb solenoid accounted for), any "buzzing" would pretty much have to be a bad connection arcing.


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## jhngardner367 (Apr 5, 2011)

True,..it would be easier than pulling the head.
However,I'd be more inclined to check the coil,or the CDI(Digital Advance Unit) ,if it has weak spark.
Seems I recall,they had a tendency to act this way,if the Digital advance unit was failing.


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## fireflyer141 (Nov 22, 2017)

jhngardner367 said:


> True,..it would be easier than pulling the head.
> However,I'd be more inclined to check the coil,or the CDI(Digital Advance Unit) ,if it has weak spark.
> Seems I recall,they had a tendency to act this way,if the Digital advance unit was failing.


How would you check the coil and CDI?


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## jhngardner367 (Apr 5, 2011)

You can't rely on checking spark with a spark plug.
Use a spark tester.
You should have a strong ,blue spark.
If not remove the cooling shroud,and check to see if there are any visible cracks on the coil.
Next,check to see if the air gap between the coil legs and the flywheel is 0.010".
If you have an ohm meter Check for resistance between the plug wire,and the kill wire tab,...should be 3k,or less.
If the coil checks out,ok, and all safety witches are good, move to the CDI,..if it has one,,as some did,and some didn't.
Can you post the exact model #,of the tractor?
It can then be determined if it DOES have a CDI .


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## Bill Kapaun (May 8, 2007)

fireflyer141 said:


> How would you check the coil and CDI?



I'd suggest looking in the Service Manual to get the CORRECT procedure.
See attached pdf for HOW.

This is your engine-
https://www.partstree.com/parts/koh...fhp-16hp-11-9kw/ignition-electrical-5-27-210/


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## fireflyer141 (Nov 22, 2017)

Bill Kapaun said:


> If you want to follow the guy that suggested you change the head gasket-
> I'd suggest looking in the Service Manual to get the CORRECT procedure.
> See attached pdf for HOW.
> 
> ...


I'm going to try to isolate the electrical interlocks before digging deeper in the engine. I think you are on the right trail with that suggestion. As I understand the information, I only have to remove the kill wire from the coil to check if it works or not.


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## fireflyer141 (Nov 22, 2017)

jhngardner367 said:


> You can't rely on checking spark with a spark plug.
> Use a spark tester.
> You should have a strong ,blue spark.
> If not remove the cooling shroud,and check to see if there are any visible cracks on the coil.
> ...


Model # is 917.271121


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## jhngardner367 (Apr 5, 2011)

The "other guy",Mr.Kapaun,realises there may be other causes,.just as I realize,how on the other forums,you're on,you pretty much control them,...being an "engineer",and all.
I'm stating things from 30 yrs of working on them,not sitting and reading about them.
He is free to take,or leave any advice.
Just as you're free to .
Perhaps not trying to be a know it all,would get you further,eh?
As for fireflyer141,good luck,with whatever you do.


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## Bill Kapaun (May 8, 2007)

fireflyer141 said:


> I'm going to try to isolate the electrical interlocks before digging deeper in the engine.....
> I think you are on the right trail with that suggestion...
> As I understand the information, I only have to remove the kill wire from the coil to check if it works or not.


Not sure what you mean by "isolating the interlocks".
Start simple & work back.

Disconnecting the kill wire removes the possibility of anything other than the coil being the problem.

Removing the relays (temporarily) will at least indicate if they are the problem. OPR1 is the one that matters, but I'm not sure how easy it is to identify it from the other 2.

The seat switch provides power TO the relays. A problem there would act just like a bad relay.


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## fireflyer141 (Nov 22, 2017)

No offense meant, just exploring all options.


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## Bill Kapaun (May 8, 2007)

Check out this forum where they made me a featured member of the month because of my electrical expertise with Craftsman tractors.
http://www.mytractorforum.com/267-mtf-featured-member-month/531057-march-fmom-bill-kapaun.html


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## FredM (Nov 18, 2015)

it only takes a few drops of water in the carby to cause backfires and too much water in the fuel will kill the engine by blocking the main jet, pull the stop solenoid from the carby bowl and do this easy check, place a small container under the carby and catch the fuel and check for water.


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## fireflyer141 (Nov 22, 2017)

Did some checking recently and found that the coil was not checking out. (I did buy a spark tester). Replaced it and the engine runs a lot better, but... Surging RPM. I do believe my next step will be the head gasket. Thanks again!!!


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## Bill Kapaun (May 8, 2007)

I think I'd try some fuel system cleaner with FRESH fuel first.
Unless you are getting a lot of white/blue smoke, a head gasket is unlikely the problem.

Surging tends to be caused by a lean condition.
A passage in the carb might be slightly gummed up.
Vacuum leaks in the intake system can also be a culprit.


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## jhngardner367 (Apr 5, 2011)

Despite my immature reaction to Bill's posts,I HAVE to agree,with him.
It's not the head gasket!
Follow his advice!
You may,also put 2 oz of SeaFoam ,in the fuel.


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## wjjones (May 28, 2010)

Seafoam is a very good product.


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## pogobill (Jan 31, 2012)

Any resolve to your backfire issue fireflyer141?


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## fireflyer141 (Nov 22, 2017)

Finally put a head gasket on it yesterday, it runs like a champ! I did clean and blow out the carb, not much to them really, and removed the limiter cap from the mixture screw so I can adjust as needed. The rear intake gasket looked suspect as well. Mowed really good until the left mandrel broke! Removed the deck and a bracket on the left side of the frame is broken too. It’s a pretty stout bracket, can’t imagine why it broke too! I think it is a pivot bracket, but I can’t find it in any schematic anywhere! Any ideas? 
Thanks again to all the responses to my issue! It’s nice to know us DIY’ers can get answers.


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