Kohler magnum 18

I picked up a craftsman mower with a kohler opposed twin on it knowing that it needed a fuel pump. Well that turned into a whole deal. Couldn’t get it pumping and now it does and runs but if it sits the fuel drains down into the filter and you have to crank it for a while. Also threw a coil on it because it was missing and eventually not running at all on the left cylinder (sitting on the tractor.) It ran better. I had to put fresh plugs in it because it fouled them out but it was still misfiring on the left cylinder. So now it doesn’t run at all because the plugs are black. Does anyone have experience with these that can tell me what I can do about the rich running? I’ve heard that they need regular valve jobs. I put a gas pedal on it and separate headers with small mufflers if that helps.

Check your idle adjustment, tune it in a little ways until it starts to sputter from running lean, then turn it back out until it again idles rough, then find the happy medium between the 2 (EG, runs rich at 3 turns out from minimum, runs lean at 1 turn from minimum, set to 2 turns for ideal performance) That was what I was taught at least. Never owned or worked on a magnum, but I can tell you that IMHO small engines just naturally make slightly more carbon than other engines and even a healthy engine can (not the best state to be but they do fine) carbon the threads of the plug a bit. Mine does it regularly and gas mileage seems acceptable. That said you definitely have another issue at play if it’s stalling. Are you getting more smoke than usual? Oil seepage is the best I can come up with. Also, have you tried cleaning the carb out? Hope this is helpful, not the smartest guy on here but hey, I try.

Yeah I know all about the tuning. It has way too much carbon. The Briggs 12.5 on my Murray and the Tecumseh 5 horse on my mini bike have excess carbon but not like this. No oil smoke but it definitely puffs a little from too much gas. My buddy blew out the jets when I first got it but it wasn’t really dirty. It was running great on gravity feed when the pump was bad but now it’s really rich. Maybe the float is set a little too low and it seeps a little extra gas. Idk. I gotta grab some plugs and see what happens. My first instinct is to put a smaller jet in it because I work on dirt bikes but I imagine I can’t get a smaller one.

Update: I torched the plugs yesterday and it fired up after a few cranks because the gas was way down in the line. It ran good for about 5 minutes but I think it started to foul the plugs after idling for a few minutes because it kept cutting out and shutting off. I pulled the carb, manifold, and other stuff off the front of the motor because I need to replace gaskets and there was quit a bit of crap in the carb. I’m thinking that the first time I cleaned the carb and ran it on a gravity feed tank it was fine but once I hooked up the new pump it blew a bunch of sh*t into the carb. Still doesn’t really explain the dying after a few minutes of running but the problem may have been there before and I didn’t know because I was running it on throttle. Also it’s idling pretty low because the gas pedal is set weird so that might be a factor. The low speed air screw may be set way out. I’m going to go into the carb tomorrow, I just dropped the bowl today.

I’ve seen it too where crap can come from the gas can and/or tank sometimes and mess with the carb that way too, but it’s rare with a fuel filter. I wonder if maybe the coil is producing intermittent or little spark and causing incomplete spark, thus not burning the fuel completely? Then again that’s just my 2c and it’s not a very good currency to invest in 

I already replaced the coil and it has pretty good spark with clean plugs. I am running autolite plugs rather than NGK but I’ve never seen an engine sensitive to plug brand. I did go into the carb and the air screws were at 3 turns out on low and 2-1/2 on high. Drained the oil too and it was very thin and smelled gassy. I’m going to pick up some oil and fresh gas and start it up. I’ll let you know how it goes. I’m wondering if it was just flooding out from the air screws being so far out…

Good news! She runs like a TOP. I guess I made this whole deal out of a dirty carb and bad air screw settings but now everyone can know for the future. I really need to get my throttle pedal working good because it’s just on or off.

MudMachine95 wrote:

I already replaced the coil and it has pretty good spark with clean plugs. I am running autolite plugs rather than NGK but I’ve never seen an engine sensitive to plug brand. I did go into the carb and the air screws were at 3 turns out on low and 2-1/2 on high. Drained the oil too and it was very thin and smelled gassy. I’m going to pick up some oil and fresh gas and start it up. I’ll let you know how it goes. I’m wondering if it was just flooding out from the air screws being so far out…

Not to bombard, but that sounds like a leaking needle and seat or a bad float. I’d look into the carb again if possible.

I was kinda thinking that. But it coulda just been because it was dumping gas into the cylinders before the air screw setting. I let it cool and started it again and it started up and ran, just took a minute to fill the bowl with gas. I’m considering a pulse pump swap.