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Kent

Walbro carb on Kohler Magnum 12

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Kent

No,it's not on a Simp, but rather a Gravely...

Tried to mow yesterday, and the tractor would sputter and die every time it was pointed downhill. Sounded like a fuel starvation issue to me. I'd wrestle it sideways on the hill so I could put it in neutral, and it would start back up. Did this at least a dozen times before I quit in frustration and was running short on time. I'd quickly checked fuel flow by pulling off the gas line on the carb side of the fuel filter -- it seemed fine.

Today, I removed the gas tank and rinsed it out as best I could -- getting a few grass clippings out, but nothing really significant. Replace the black plastic fuel filter with a clear, see-through filter so I could watch the fuel flow. Pulled the bottom bowl off the carb and removed the small amount of sediment in it, then reinstalled it. While I had the air filter off (which was quite clean), I dumped enough Sea Foam in it to kill the engine, then let it sit per the instructions. Then restarted it, and ran about a quart or so of gas (which was fresh) through it, with a higher than usual mixture of Sea Foam in it. Finally, I added the 1 oz of Sea Foam per gallon of gas to a full tank, and finished mowing the yard.

I was reluctant to do anything more to the carb because (a) I know NOTHING about Walbros, and (b) I didn't have a gasket set on hand.

While I was mowing, the symptoms were reversed -- today it wanted to spit and sputter when pointed uphill. Downhill or around the slope was fine. When it was sputtering, it was puffing black smoke, and the new fuel filter seems to always have sufficient fuel in it. The engine didn't die quite as often, and I was able to finish mowing the yard. It may be my imagination or wishful thinking, but I THINK the symptoms got a bit less the longer I mowed.

Any ideas what's causing this?

It certainly doesn't seem to be a fuel starvation issue:

-- fuel filter shows good flow,

-- when the mower is pointing uphill (like today), that's optimum for gravity feeding the carb from the gas tank

-- puffs of black smoke would tell me it's getting fuel

I'm guessing it's something with the carb, but I know nothing about these...

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HubbardRA

Sounds like the float is set just a little too high. Probably will always run good on the level. On the slope it is flooding the plug and getting it wet. When you go back to level the missing will start to die down and eventually go away when the plug is completely dried out.

Another thing to check is the plug number. I think the Magnum 12 is basically the same as a K301 and should have an H10 Champion plug in it. A plug that is a little too cold will also start to miss just from fuel slosh on a slope and will not clean out quickly.

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Kent

Thanks, Rod. I'll check the plug first. If that doesn't do it, I'll reset the float. It had been running fine, since the spring servicing. I'd mowed my yard twice before, without issue.

It's always had the tendency to rumble/stumble intermittently at 1/2 to full throttle, especially if not under a heavy load, but most Kohler singles I've seen seem to do that -- kind of like an occasional misfire. The governor linkage would move and it would immediately recover. Under load, it ran fine. It did and still does idle quite smooth.

Like I said, I know nothing about these Kohler singles. My only other Kohler is the CH25 twin, and it's a totally different animal.

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motorhead110

Kent,

Just last week a had a VERY similar probler with my K-181 with a Carter on it. i tore it apart and cleaned the crap out of it. Then I tuned to factory specs and runs like new.

Hope this helps!

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HubbardRA

Kent,

Check the choke plate to make sure it is completely opening up. Also some of these carbs had a small spring-loaded vent in the choke plate. Those tend to come loose and go into the carb or even into the engine. The carbs are relatively simple.

Check the governor to make sure it is moving smoothly and not hanging up. I adjusted one and pushed the arm against the block too tightly and it would hang up. Just loosened it and pried it out just a bit and it worked very well. You adjust the Kohler governor same as the B/S.

Make sure you still have the lightweight spring on the governor linkage to eliminate movement from vibration. Not having that spring will cause an occasional missfire. If you do not have that spring, then any very light spring that is hooked between the governor link and the throttle plate will stop the movement of the throttle plate from vibration and the looseness in the linkage.

Working on a Kohler is essentially the same as working on a B/S. Nearly everything is done the same way. Just a different type carb and the governor linkages are different. Also the old K-series Kohlers had external coil ignitions and no magneto.

Hope I have helped you in some way.

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powerking_one

Kent,

Is this a Kohler M-12/K-301 engine on the Gravely? Rod implies that it is. Late models of Walbro carbs use a plastic/nylon float and usually are not subject to failure/leaking fuel into them; but that is still a possibility. Also, I would check the fuel bowl vent (a drilled passage I think around the choke plate area. You could have a small piece of debris lodged in the float valve needle/seat also. This has happened to me a few times with the Walbro WHG carb on my Gravely/Tecumseh OH-160 (even with inline filter); gas dripping out the bowl vent. Seems these carbs are not very tolerant of any tiny pieces of debris getting into the fuel supply. I've been getting Walbro OEM parts through Jacks and prices are very reasonable.

Just my 2 cents worth....

Tom (PK)

PS let us know what you find....

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Kent

Tom,

Yes it's an Magnum 12. It was originally a 10HP, but the PO put a 50" deck on it, and the 10HP wouldn't run it to his satisfaction, so he had a Magnum 12 put on it. This is the beast that I got to mow my steep hillsides - without the sulky of course... The steering brake lets me crab it and keep in on the slopes, while the duals (now with snowblower tires) let me climb them and keep it shiny side up...

gravely_left.JPG

I'll have to get a carb kit and gaskets, so I can remove the carb and check it. I'll report back...

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powerking_one

Great machine you have there Kent; my 546 (Commercial 12 class like yours) is my New Hampshire life line for snow blowing with the "Snow Cannon" MA-210 blower. I custom re-powered it in 1996 with the Tecumseh OH-160 and it is unstoppable. Gravely designed this gear transmission to handle like 35HP way back in the 1930's. This tractor will no doubt outlive you (LOL). Now compare this to the MTD, etc cheese-master crap at the big "box" stores.....

On a side note my 1963 Sears/Whirlpool washing machine is still going strong after a co-worker gave it to me in 1984 and I rebuilt it. Kind of like NASA grade mil-spec stuff back in "old" days.....

Tom(PK)

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powerking_one

Kent,

On a side note, since these Walbro carbs can be cantankerous with problems you are seeing, I would suggest replacing it with one of the old tried and true Carter model N carbs; lots of them out there; fully adjustable Hi/Lo circuits; Kohler had it "right" before they were transitioned over to the fixed jet Walbros.

JMHO

Tom(PK)

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motorhead110
quote:Originally posted by powerking_one

Kent,On a side note, since these Walbro carbs can be cantankerous with problems you are seeing, I would suggest replacing it with one of the old tried and true Carter model N carbs; lots of them out there; fully adjustable Hi/Lo circuits; Kohler had it "right" before they were transitioned over to the fixed jet Walbros.JMHOTom(PK)


id="quote">
id="quote">Tom, A Walbro Model N will not fit on a magnum 12. In fact, last week i took a Kohler adjustable jet carb off of a K-301 and tried to put it on my K-181, The bolt holes are different (Where it goes into the motor.). I suppose you could create some type of boot/bracket to make it work.

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HubbardRA

Brenden,

Being that the K-181 is much smaller than the K-301, it uses a much smaller carb. Yes, the bolt holes are different, and the K-301 carb is much too large.

A K-301 carb should, however, fit on an M-12. They are the same size engine, so the carb should work great on this engine. Tom was correct.

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powerking_one

Brenden,

The Kohler/Carter Model N carb was a generic body in that they share the same overall bowl & float dimensions. There were at least 3 variations of mounting flange geometries that I know of; namely the little "guy" K-90/K91, the K-161 through K-181, and the K-241 through K-341. The intake bolt patterns were all different in these famililies. Thus you cannot take a K-181 carb and bolt it onto a K-301. Also, Kohler/Carter stamped the venturi sizes in (32nd's of an inch) above the choke plate into the casting. Thus 26 for a K-241, 30 for a K-301; etc.

Yeah, so no surprise in your attempt to fit a K-181 carb onto a K-301/Magnum-12 not lining up.

Tom(PK)

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Kent

Just remembered that I hadn't closed the loop on this...

A good cleaning seems to have solved the problem. I still may need to tweak the float setting a bit, but for now it's back to running great under load. Still rumbles/stumbles occasionally at higher throttle settings with no load, but it's always done that...

Thanks everyone!

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powerking_one

Kent,

I'm not surprised you have midrange "stumbling" problem with this Walbro, my OH-160 does a similar thing (and why I don't like these Walbro's). A good healthy Carter N (tight throttle shaft, proper float height/etc, properly adjusted)never exhibit this type of performance problem IMHO.

Tom (PK)

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