Exmark engine bogging under load?

[fireman32]

52 inch commercial exmark, Koehler two cylinder engine, think it’s a 27 hp.
New plugs, fuel filter and air filter. Cuts fine until you get into thick grass and it has a little miss while idling. Whenever it bogs, it’ll have a good bit of black smoke exit the muffler. It will return to full throttle pretty quick after you stop for a second. It’s always been ran with non ethanol fuel.
I’m guessing the carb is going bad? Or would a coil pack cause this problem? The old plugs weren’t fouled just a little black.
It’s about 10 years old and has never had carb work done on it.
Thanks for any help.

 

[NE GA Pappy]

it is flooding a bit. When is the last time you changed the air filter?

 

[fireman32]

Seems to be flooding little, air filter is new. That’s kind of why I was thinking the carb diaphragm may be getting worn

 

[NE GA Pappy]

Seems to be flooding little, air filter is new. That’s kind of why I was thinking the carb diaphragm may be getting worn

carb diaphram? Usually a bad part = less fuel, not more.

If it is a new air filter, the first thing I would check is to make sure all the jets are seated well and not vibrated loose and allowing gas to go around the metering orifice. While I had it off, I would check the float real close. Make sure it is not gas logged or has a crack in it allowing fuel inside. That will make the fuel level high, and cause it to flood

 

[Bigtimber]

Whats the model number and spec? Should be on a white sticker on motor.

 

[fireman32]

It’s over at my in laws, I’ll get the numbers in the morning.

 

[DRBugman85]

Whens the last time valve lashed was checked, adjusting the valves has a lot to do with the performance of any lawn mower engine.

 

[fireman32]

Whens the last time valve lashed was checked, adjusting the valves has a lot to do with the performance of any lawn mower engine.

Never been checked

 

[Hillbilly stalker]

You might wanna check the govoner linkage. It sounds like it's throwing the choke to it when it gets in a bind. First thing I would do is pour some Sea Foam in it and run it. Very likely you might need to adjust or re-seat the valves. Does it back fire any when you shut it down ?

 

[fireman32]

It takes awhile to completely shut off after the key is turned off. Doesn’t normally back fire, just does what I call dieseling.

 

[Hillbilly stalker]

That sounds like the valves to me, but I'm just a shade tree mechanic working on my own junk . When you shut it off hot, does it have trouble starting back up while still hot ?

 

[fireman32]

No it starts right back

 

[fireman32]

Im a shade tree too, just hate spending money guessing sometimes.

 

[Hillbilly stalker]

I'd try that Sea Foam in the fuel first, and pretty stout. It will clean a lot of impurities and old carbon exhaust off the valves. That would be the cheapest and easiest first step and it cannot hurt anything. Just make sure you get the can that says " fuel treatment". They have a transmission treatment can that looks a lot like it. Advance auto, Napa, Oriely's and Wal mart has it. It's great stuff. If your old plug was fouled up pretty bad, that would be a tell tale sign too.

 

[DRBugman85]

Never been checked

Check the valves,run Sea Foam fuel treatment,I use non-ethanol fuel cheaper than a new mower.

 

[rayjay]

Sounds to me like it's running rich. Pull the spark plugs and see what they look like. Maybe the choke is not fully open. Usually ope engines run lean not rich.

It's also common for ope twins to be running only on one cyl due to a bad coil or plug. You would think it would be obvious but the governor compensates.

 

[NE GA Pappy]

It's also common for ope twins to be running only on one cyl due to a bad coil or plug. You would think it would be obvious but the governor compensates.

usually you can hear the dead miss at idle speed if it is a bad coil or plug, but not always. I like to run the engine up to around 1800 rpm or so, and pull the spark plug wire off each cylinder. You will hear a huge drop or kill the engine if only one plug is firing.

The Kohler engines are not as bad to have bad coils as the Kawasaki engines in my experience.

I still think it is a over fuel issue and not a firing issue, but I've been wrong before.
Check the choke plate to make sure it is all the way open, then I would check the jets and the float in the carb

 

[rayjay]

I forgot to say pull a plug wire one at a time. I've never messed with a Kohler twin only the Command singles. I HAVE had Kawi and Briggs twins with a bad coil.

What I used to do on car motors with a dead cyl was when starting from cold I had a spray bottle of water and I would go around spraying the ex manifolds and pretty quickly you could find the dead one. Of course, don't work if the motor is already hot.