1996 917.256591. Kohler CV-15s. Was flooded yesterday. Died in middle mowing. Has a Nikki carb 12 053 68/12 853 68 that does not look to be the most common animal. It has been replaced once and the old one hunted real bad. Here's my issue now. I will be mowing for any amount of time 15 mins to over an hour and it is fine. I bag so when I stop to empty I either throttle down all the way and leave running or shut down to go light up pr grab a drink. Usually seems fine - I throttle up and engage and go on with the job. Common episode is after dumping last bag I do not engage and throttle up and it starts hunting/sputtering and dies. Sometimes it does this in the middle of mowing.

Initially when issues started airbox/carb looked dry and worked for a short second w/a shot of starting fluid. Replaced cap as appeared might be a vent and went without issue for a few weeks. Yesterday ran for about 20 mins and died in middle mowing and the airbox was flooded with gas??? Should not have anything to do with the solenoid, but swapped out the old one, changed oil as it now smelled like gas, and mowed just fine until done (1hr) and let idle 5 mins when dumping. Then throttled up again without engaging to put away and here comes my hunt again. This is what usually happens. Was too ticked to open the airbox to see if starved or flooded. Does this sound like a carb issue? Intermittent flooding or starving??
1. If carb I can find no rebuild kit for Nikki. Also recall reading that these have something in needle seat that do not respond well to rebuilding if a float/needle issue?
2. I have read of an "atmospheric vent" on a carb getting clogged?? What is it and where is it on this carb?? Why can't I find any info about this dang carb???
3. Any possibility that this can be a spark or coil issue?? Why would this cause flooding?? Or drying for that matter?
4. Would love to swap this carb out to Walbro or something else as these have a ton of info but not Nikki and the SOB is $100 if I have to replace again. Have been told it is not a possibility to change out carbs to different make?
Can someone please help??? This is driving me nuts.

The atmospheric vent is simply and external vent into the float bowl of the carburetor. It must be open or pressure will build up within the float bowl and hold the float down allowing fuel to continually flow through the carburetor. If the carburetor is flooding enough to contaminate the fuel, then the engine should be running poorly, and you should have a great deal of soot on the spark plug and out the exhaust. A dirty air filter can cause this, but should also make the engine run poor.

Does the engine smoke when running?

Is there any indication that fuel is leaking out of carburetor, when the unit is parked and not running?

30 Year,
Thanks for responding. Yes I changed the oil because it smelled like gas yesterday. Does not right now but it is brand new so if there is any fuel contamination it is minimal.

I did start it up this morning and ran an fast idle and looked fine. Then moved to slow idle with the airbox open and saw small amount of fuel blowing back from the small vent hole in the air box that comes from the vent tube on the front valve cover if that gives any more hints. Coming from there seemingly does not sound good. I left for a couple of hours and it was still moist when got home but not pooled. It does not smoke when running at full when running OK but does when it surges before dying. It does sometimes gett the Kohler Command puff at startup sometimes. iAny other thoughts with that info?? Thnx much.

Blow back from the breather tube, could indicated a bad breather valve, or a blown head gasket, or simply overfull crankcase. Usually this will cause an engine to smoke. If the engine is running good then it's hard to imagine a carburetor that's flooding, as this would cause the engine to run poorly.

30 yr couple more questions relative to your answers. The new oil is getting faint smell of gas.
1. can a bad fuel pump contribute to and flooding on this model? it is mounted on the other side of the engine and lookd like it gets diaphram pulse from crankshaft?
2. can a feasible compression test be done on this motor. reading tells me has some kind of safety compression release? How check for a bad head gasket?
3. Would a bad breather valve cause an issue with gas to the oil?
4. found a carb rebuild kit for this pup. 12757 27s. It is $47 for a rebuild kit??? wow. any experience with these nikki's? am i better off buying a new carb?

honest - it seems to run fine with blades engaged and mowing for sometimes over an hour. this just happens sometimes but now I am worried about gas in the oil and want to do something before I lose the motor. though the sound of a new broadmoor vanguard sounds sweet...........thnx for all your help

1.) Yes, It can also be the source of fuel in the crankcase. A leaking pump diaphragm can allow fuel to enter the crankcase via the pulse hose, by passing the carburetor altogether.

2.) Cylinder leak down test.

3.) No

4.) Limited experience with Nikki on this engine, much more experience with Walbro. In either case, I don't think the carburetor needs a rebuild, a new float and needle seat at most, if it's actually flooding. I would take a closer look at the fuel pump at this point.