M-18 running issues
 

So i noticed today after mowing for 20 mins my 1872 starts loosing power. Turn the deck off and its surging and spitting. Ive rebuilt the Walbro carb. Cleaned the lines and tank and put a fuel filter on it. It did great last Friday mowing but now it runs like crap until it sits there running for a bit it runs like normal. Any ideas? Never really had a magnum motor before

It sounds like it is starving for fuel. Try pulling the choke when it does that, and if it helps, then I would look @ removing the carb and looking for chit in the bowl, especially the main jet circuit. If it is a non adjustable type of carb, most replace them with the adjustable type.
Also look for water in your fuel. You could have fuel pump on it's way out or chit in the valves inside it also.
--------just some things to check.

It is not unheard of to get a bit of fuel hose in the fuel system when removing/installing/ working on the fuel system.
Let us know what you find.

I would clean everthing again and replace the fuel lines. After that sounds like it could be the pump.

Im gonna yank the carb off clean it again. Everyone said go with a carter style carb like on a single cylinder Kohler. It runs great no load but load it and it acts stupid. Really hope if it is the fuel pump it can be rebuilt or cheaper than what I've seen so far.

Electric ones are $50 at Napa.
Put in three now and like them.

You can get aftermarket fuel pumps on eBay for under $40.

Stens pumps are good. Installed them with good results. So are Prime Line pumps.


I personally prefer not to go electric, but that is an option. But Terry is correct also. Those will work well too.



I agree that it sounds like it's starving for fuel.... but I'm not convinced it is the fuel pump. How does it run when the fuel tank is full? Does that help it?

it runs fine full or close to empty. i did take the carb back apart and soak it for an hour in cleaner. i did find some trash that came from the pump after flushing it...i got it back together just didnt get time to fire it up. what i did find in it was some kind of fuzz or something wasnt sure....time to download the manual for the motor and find the settings for it and from there

It is not much money to change the lines, just a little hassle. I would still do that.

So ive replaced the lines. Rebuilt the carb again. Rebuilt the fuel pump using all genuine Kohler parts it runs better but it seems like the governor is not right. Any idea how its adjusted?

It is covered in the free service manual from kohler avail in out resources section, on page 3 near the bottom.:beerchug:

Im at wits end with this thing. Just started mowing again and not even 50 feet it starts falling flat again and started surging. Pull the choke all the way out it runs fine. It is just better to junk the walboro carb and buy a new one off the net?

I recently got my butt kicked by one of the non-adjustable carbs on a M18, I replaced it with a used adjustable jet style off a blown KT17 I have. The only thing I can figure is I did not pull the welch plugs out and there is still crap in there, although in my case it is possible someone else messed something up internally because the carb had been recently "monkeyed with" trying to solve a poor running issue. Not saying you need a new carb, just that I had a couple folks tell me they have no luck rebuilding the ones without an adjustable jet.
Best of luck.

Im looking online at some but im tired of messing with it.

Do you have a fuel filter on this thing?? You said you did in post #1, but what kind is it? Is it a filter, or a screen?


I do not understand why people have so much trouble cleaning out carbs. I just don't get it. I've had people bring me carbs off tractors out of junk yards to rebuild for them that literally were full of rust. Nearly solid full. Like all the passages full of rust and packed full of crap... and I didn't have any issues rebuilding it and giving it back to them and it worked on the first try. What can we tell you that will make it easier for you (and all the others that struggle with this process)? Would a video help? There are only so many passages on this tiny little carb, and they all have to be completely free of dirt. COMPLETELY. I spray brake cleaner into each of them and watch for it to spray out all the ports. You can't see compressed air, but you can see brake cleaner spurting out. (WEAR SAFETY GLASSES!!! Brake cleaner in the eye hurts like hell!!!) I just don't know what to tell you that will help. You don't have it clean yet. You need to flush the system again. You probably should buy another fuel filter, just to be sure that it's good.

Sure. Buy a new carb. Easier that way. BUT,,,,,, if you have junk in the fuel system, or a bad filter, or a bad pump..... it's just going to do it to that one too.

You are sure you have the direction for the filter going the right way correct? Is it allowing flow enough to feed the Mag 18??? Not to small or restrictive?

I had an issue near this and a new pump fixed it.... make sure your float and seat are set properly as this will alter the amount of fuel in the bowl...

Governor adjustment is easy for the surging issue once you get it running under load.

J Mechs comments above are spot on for the carb cleaning aspect....

Good point. Those mags drink fuel like there is a hole in the tank. Every part of the fuel delivery system needs to be working.

Never figured out if mine is still clogged internally or if the last guy working on it screwed something up trying to clean it out by poking drills and wires in places he shouldn't have. I mean after all, he glued the fuel bowl back on. :bash2: Anyway, I'll probably try it again one day--soak it out again, but remove the welch plugs this time. I do have a KT17 that needs a cleaner/better carb.:biggrin2: FWIW, I replaced all my lines, washed the tank, and replaced the pump.

If you pull the choke and it runs better, it's clogged up. If it is overfueling, then he may have gotten a hole too big. FWIW, I prefer the adjustable unit's also. But I also have lots of carbs sitting around, so all of mine are adjustable. May have been a regional thing too.... I don't know that I've ever had a Cub that didn't have an adjustable carb. Maybe I am just lucky. I've not ever needed to remove a welch plug on these little carbs. Not saying that isn't a good idea if you can't get it clean though.

So, not trying to derail the thread from the OP, honest. We couldn't make mine run correctly even with the choke on. Really are leaning toward something modified/damaged during prior repairs.

So regarding adjustable carbs, does anyone know a source of used ones--as in what engine? My M18 in my 1811 had a fixed jet. I have a parts 682 with 2 blown engines--the first was a series 1 KT17, it had a fixed jet. The replacement series 2 had the adjustable that I robbed for the M18. I have no idea what carb is original to any of the engines, other than the one on the series 1--that engine blew at 200 hrs.

Series 1's are adjustable from factory
and ebay has $20-25 NEW ones that seem to have a good reputation.
While I can make non adjustable ones run as they should, I still don't like them.
They are lean to meet emissions.

Now you got me wondering did the owner swap the series 1 carb over to the series 2, before that one blew? I do have a series 2 in a 782--non adjustable as well. That one runs OK, just needle isn't sealing--got to fix that.
I shouldn't say this, I have no idea whats on my 2072, but its been working proper since the day it got here!:bigeyes:

well j mech i took it back down to nothing. knocked the welch plug out and there was some trash in behind and so i got that cleaned out. as far as the fuel filter goes i have a pretty big one on it and it flows pretty well without it running turn it over and it sprays like no tomorrow...i think the pump is good cuz when i took the line off it had pressure on it and squirted out of the line fromthe pump to the carb. im gonna give it another shot...if i cant i get it to run right this go around im gonna drain the fuel tank again and go from there

If you found trash in the carb, I'd say that's your issue. Question is, did you get it all out....

I got it all out of the carb and also found out the emergency fuel shut off was bad (little plunger with the o ring) took it out and it has no issues now

OK, this is something I missed on mine evidently. :bigthink: Would you elaborate more on this please?

You mean a fuel shut off solenoid? Mag engines don't have one .....:bigthink::bigthink::bigthink:

What are you talking about? Need a pic of this.:bigthink:

The last of the magnums had a fuel shut off,and the later replacement engines also came with the shutoff in the carb.1991 2082 with 435hrs pic. of shutoff.

Thats it. Unhooked and no more issues

:bigeyes: That's what is good about this forum, always something to learn!
Wonder why Kohler wanted that? I've toyed with the idea of adding an electric fuel shut off so I don't have to worry about the needle not sealing and flooding the engine while sitting. As it is now, I have easily accessible manual fuel shutoffs on 2 magnums, 1 KT, and an Onan---yes we close them every time we are done with them.

John,
I think they used them to stop run-on after killing the ignition.
Also might be for emission reasons. :bigthink:

From what ive gathered it was to meet emissions and such. Ive mowed some lately but not really pushed it yet. I did over load the engine trying to turn speed up amd raise the deck all at once. But what i did mow was pretty tall and thick and never hit the governor on it.

John,
It does not stop the fuel into the carb like a petcock would.
It stops the flow from the float chamber to the venturi/idle system.
So no back fire into the muffler and lowers emissions.
Many engine/vehicle manufactures did that to lower the level.
As the standards got tougher, the engine design had to change.
We even gotten to the point of fuel inj on most everything.
Ya the air is cleaner,but @ what cost??
but that is for another topic @ another time.