Kohler Magnum

[Dennis C. 142]

I have a 1986 312-8 with a Magnum 12hp engine. This is not the original engine so I have no idea how many hours on the engine.

From 1/4 to full throttle the engine runs OK but below 1/4 to idle there is a occasional miss. Is this normal?

[pfrederi 18,660]

Have you tried adjusting the idle mixture needle.

[Maxwell-8 4,367]

No, probably the carb is a bit dirty. 

 

 

[The Tuul Crib 7,339]

I would suggest doing a complete tuneup including valve adjustment and new head gasket. And yes even the carb!

[clueless 3,232]

My 1989 312 magnum has a slight miss even at full throttle, had it since I've owned it ( 14 years) might be the nature of the beast. You should run it at full throttle all the time so not really a big problem.  If you don't like the miss, pull the carb and rebuild it.

[953 nut 59,912]

If you are using gas with ethanol STOP!  You can find a station that sells ethanol free gas here     https://www.pure-gas.org/

[The Tuul Crib 7,339]

40 minutes ago, 953 nut said:

If you are using gas with ethanol STOP!  You can find a station that sells ethanol free gas here     https://www.pure-gas.org/

[Dennis C. 142]

1 hour ago, The Tuul Crib said:

I would suggest doing a complete tuneup including valve adjustment and new head gasket. And yes even the carb!

 I have no idea how old this engine is as the engine is not the original engine.  It starts up no problem, governor works and  there is no miss above 1/4 throttle. All new fuel lines, fuel shutoff with filter, secondary filter before carb and the previous owner rebuilt the carb before I bought it. Valve adjustment and head casket removal is not my  forte. No one in my area works on Kohlers which means I would have to travel.

 

1 hour ago, The Tuul Crib said:

I would suggest doing a complete tuneup including valve adjustment and new head gasket. And yes even the carb!

 

[The Tuul Crib 7,339]

49 minutes ago, 953 nut said:

If you are using gas with ethanol STOP!  You can find a station that sells ethanol free gas here     https://www.pure-gas.org/

How often do they update this list ?

[953 nut 59,912]

10 hours ago, The Tuul Crib said:

11 hours ago, 953 nut said:

You can find a station that sells ethanol free gas here     https://www.pure-gas.org/

How often do they update this list ?

Much like RedSquare the pure-gas site is a user driven site. A new station can be added or one that no longer has ethanol free gas can be removed to keep the site up to date. If a station listing in your area isn't up to date you can do everyone a favor and correct it.

[peter lena 9,255]

@Dennis C., you never mentioned trying a cleaning agent like SEAFOAM , similar problems solved with the nozzle extension into a running engine , backed up with a hand covering carb under speed , forcefully sucking and cleaning its way thru , has done it for me . also agree with others on the carb rebuild , not knowing its past . add , STA-BIL gas treatment with your gas , never an issue , pete 

[clueless 3,232]

1 hour ago, peter lena said:

@Dennis C., you never mentioned trying a cleaning agent like SEAFOAM , similar problems solved with the nozzle extension into a running engine , backed up with a hand covering carb under speed , forcefully sucking and cleaning its way thru , has done it for me . also agree with others on the carb rebuild , not knowing its past . add , STA-BIL gas treatment with your gas , never an issue , pete 

The only reason to run it at 1/4 or less throttle is to let it cool down after using it awhile on a hot day for 10 or 20 seconds before you shut it off. So the slight random miss is kind of a moot point. 

[The Tuul Crib 7,339]

38 minutes ago, clueless said:

moot point. 

??

[Stormin 9,984]

3 hours ago, The Tuul Crib said:

??

 

Debatable!

[Dennis C. 142]

6 hours ago, peter lena said:

@Dennis C., you never mentioned trying a cleaning agent like SEAFOAM , similar problems solved with the nozzle extension into a running engine , backed up with a hand covering carb under speed , forcefully sucking and cleaning its way thru , has done it for me . also agree with others on the carb rebuild , not knowing its past . add , STA-BIL gas treatment with your gas , never an issue , pete 

Carb was rebuilt by previous owner, a Wheel Horse guy. I use 93 oct in all my mowers with Sat-Bil added. Since I'm not an engine guy I'm reluctant to check valve clearances or replace a head casket.

[peter lena 9,255]

@Dennis C., thanks for the added detail , since your issue is so small and concentrated , in addition to removing those carb  adjustment needles and blowing in some carb cleaner or sea foam, then putting them back in the same spot , see how they react to any adjustment. I would also look over your fuses and electrical connections , for any possible corrosion , usually problems come in multiple areas , just tinkering around you might suddenly gain on your issue. not going to be spot on for any problem , they are all  different , good luck , pete  

[tunahead72 2,543]

On 5/24/2021 at 3:53 PM, pfrederi said:

Have you tried adjusting the idle mixture needle.

 

@Dennis C. This might solve your problem, and it's easy.  Can you send us a photo of your carb?

 

[clueless 3,232]

Depending on the magnum, the later ones had no adjustments, EPA.

46 minutes ago, tunahead72 said:

 

@Dennis C. This might solve your problem, and it's easy.  Can you send us a photo of your carb?

 

[The Tuul Crib 7,339]

I'm going to say the carburetor is going to be a walbro. I have a magnum 14 and that is what carburetor is on it with only one adjustment. A good thorough cleaning wouldn't hurt a bit ! I just had to do that to mine. I soaked it in Chem dip for at least three or four days washed it out and then set it to the micro vibrator as I

call it!! 

The magnum is a great motor and with a little maintenance she will run like a champ!!!

[Dennis C. 142]

On 5/25/2021 at 3:21 PM, peter lena said:

@Dennis C., thanks for the added detail , since your issue is so small and concentrated , in addition to removing those carb  adjustment needles and blowing in some carb cleaner or sea foam, then putting them back in the same spot , see how they react to any adjustment. I would also look over your fuses and electrical connections , for any possible corrosion , usually problems come in multiple areas , just tinkering around you might suddenly gain on your issue. not going to be spot on for any problem , they are all  different , good luck , pete  

Thanks Pete. Yesterday I took the mower out  and started it up cold, no missing at idle but after 10 minutes of running the miss starts. So it appears that when the engine is warmed up, the miss starts. Sadly, although this tractor looks nice, the wiring has been butchered.

[Dennis C. 142]

On 5/25/2021 at 5:23 PM, tunahead72 said:

 

@Dennis C. This might solve your problem, and it's easy.  Can you send us a photo of your carb?

 

No, but I did notice that the miss only occurs when the engine is fully warmed. Doesn't happen when cold.

[Dennis C. 142]

On 5/25/2021 at 6:09 PM, clueless said:

Depending on the magnum, the later ones had no adjustments, EPA.

meant to say, yes I could send you a picture of the carb.

[peter lena 9,255]

@Dennis C. think that butchered wiring is your issue , have done a lot of recovery on those engines , and have always found a related short or related chafing issue,  especially at those multiple  Oregon connectors , had a strange one on  a horse i picked up , had a related amperage gauge issue . removing dash and verifying as I went found a cracked multiple connector as well as corrosion . bet is a chafing movement brought on by engine heat /movement. get some small alligator  clip jumper wires , to by pass the areas , once it stops  missing , you have found your problem. for what's involved you might also plan on a harness swap. you can do it , pete 

[Dennis C. 142]

On 5/27/2021 at 12:03 PM, peter lena said:

@Dennis C. think that butchered wiring is your issue , have done a lot of recovery on those engines , and have always found a related short or related chafing issue,  especially at those multiple  Oregon connectors , had a strange one on  a horse i picked up , had a related amperage gauge issue . removing dash and verifying as I went found a cracked multiple connector as well as corrosion . bet is a chafing movement brought on by engine heat /movement. get some small alligator  clip jumper wires , to by pass the areas , once it stops  missing , you have found your problem. for what's involved you might also plan on a harness swap. you can do it , pete 

Thanks for all your input Pete. Yesterday I took the tractor out and let the engine warm up since the miss isn't present cold. Sure enough after about 10 minutes the miss started at just above idle. So I took my screw driver and adjusted the idle mixture screw until the miss disappeared. Didn't need much maybe a 1/4 turn. Transition from idle to full rpm is smooth, no stumble. So after mowing season, I'll buy a rebuild kit and thoroughly clean the carb.   The tractor really had issues when I bought it, wrong size tires and wheels all the way around, so much water in the tranny that the dipstick looked like thick heavy cream when I pulled it out. I installed all new tires and the proper wheels at all 4 corners, drained and flushed the tranny several times with ATF until everything was clean. Tranny still has some squealing and lurching though. As for the wiring, I spend a full day looking into it. Seems one of the several safety switches failed and instead of replacing them, someone  cut the wiring off from the offending switches and installed a push button starter switch. You'd have to be good with a wiring diagram to fix all of this and at what cost? Yeah, I would like all the safety switches to work and all warning light on the dash to work but she's a working tractor not a show tractor.

[953 nut 59,912]

3 hours ago, Dennis C. said:

took my screw driver and adjusted the idle mixture screw until the miss disappeared. Didn't need much maybe a 1/4 turn. Transition from idle to full rpm is smooth, no stumble.

                     Gad to hear it!