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Rebuilt Fh680V approximately 300 hours ago. Running great for the last 250. Started to run a little rough at idle (sometimes stall) and now rough at wot. Went to a hotter plug NGK BPR2ES. Didn't work. Plugs are covered with soot after 4 hours of running. New carb, fuel pump, stator, coils. Still having the same issue. Oil seems to turn black with only a few hours of run time. Checked the valve clearances. Perfect. Forgot the mention the heads were completely reconditioned as well. Compression 115 on both. Black smoke from exhaust at when throttling up or engaging the blades. This engine is on a 52" Bobcat zero turn. No idea what to do next. Any help would be greatly appreciated!!!!!!

Black smoke is either rich or timing too far retarded or random missing
Both plugs equally sooty tends to point to the carb or timing key .
Does this engine have the tank vent plumed into the intake manifold ?
If so pull it off & plug the spiggot see if it is pulling fuel vapour from the fuel tank .

what conditions do you mow in? air filter clear of debris?

Make sure the choke is not stuck on all the time. Someone has done some engine work so things have been messed with.

Next check carb needle that is sticking half open or all the way open.

slomo said:

Make sure the choke is not stuck on all the time. Someone has done some engine work so things have been messed with.

Next check carb needle that is sticking half open or all the way open.

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Have found several with choke shaft clip broken and the only way to fix it to replace the choke shaft. Unless you get a 25 158 11-S Kohler bushing retainer and drill the choke shaft lever out so it will fit.

thanks for all the responses. Both plugs are equally sooty. Tried cutting today after replacing the plugs. The fouled in less than an hour to the point I couldn't cut anymore. I'm going to pull the cover to see if the flywheel key and flywheel are lined up. I don't know any other way the timing could be off. No tank vent to the manifold. Checked the choke and it works as it should and stays in place when cutting. Took the carb off (OEM carb, 100 hours on it) and it still looked new. Cleaned it and reinstalled. Air cleaner is fairly new. Took it off and ran the engine with no improvement. The choke shaft clip is good. I'm at a loss. I was going to pull the heads today just out of curiosity. I need the mower back up and running by ASAP. Please keep any suggestions coming! Kawasaki FH680v-cs05 23hp

Remove the carb. Turn it over. Pressure test the needle and seat at 7psi. Needle should hold 7psi for 30 plus minutes or more.

The below video is on a motorcycle carb. Still has most of the same parts as you have.

New or nearly new parts don't mean much if they don't work.

I did disassemble and clean but I did not pressure test it. I will tomorrow though. I'll post what I find. Thanks for the video.

does it have a smaller fitting than the fuel line fitting next to the fuel line fitting. If so make sure it is open. Some engines have a small hose running from it. Make sure the hose is open.

raisin1 said:

My symptoms also. I had bad fuel pump that filled crankcase with gas raising level of oil. Oil turned black and soot on plugs.

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More like a bad carb needle and seat that was stuck open allowing fuel to get into the oil.

Bad fuel pump wouldn't push any fuel. Unless bad meant it pushed out 20psi and overwhelmed the needle.

pulled the carb again and pressure tested it. good to go. didn't start leaking air until roughly 16 lbs. As to raisin1, I found the pipe (p/n 921917027) that goes from the bottom of the fuel pump to the left head was hard as a rock and loose. I do believe the oil smells like gas. As a matter of fact, when I checked it a few days ago it was above full a bit and I know I didn't over fill it. Even though the fuel pump is new. I'm going to change it and the pipe. Hopefully onto something. Thanks again for all the advise.

When fuel pump diaphragm ruptures fuel is sucked thru pulse tube which is under vacuum. Common problem. Sounds like your problem. About $11 on Amazon. New one wow! Don't know.

Thanks again!!! I have a good used one I'm going swap from my back up mower while I wait for the new one to come in. I'll post the results. Once again, thanks for the input

Changed the fuel pump with no improvement. Plugs fouled so bad in 20 minutes I couldn't cut anymore. Even though the OEM carb is fairly new, I'm going to disassemble and soak overnight. I already did this step minus the soak. Putting new spark in again for good measure. This one has me stumped.

OK, time to get serious with this one
Please post the full specification number so I can check exactly what carb should be there
The FH680 had 3 fitted over its life, 2 with a square cast float bowl and one with a round pressed float bowl
The service manual lists 2 different sets of main jets for the twin barrel carb body
One has an external vent the latter has an internal vent

Carb needle is obviously passing excess fuel.

I have one that pressure tests just fine. Funny but when you turn it over and install on engine, it will overfill the carb bowl and leak on the deck. Needs a new needle and seat like yours.

No other way to foul plugs in 20 minutes other than a carb needle hanging wide open. Unless you have some really weak spark??

Install an inline fuel cut off valve. Crack the valve partially open. Start and let the engine run. See if this cuts down the rich condition. Open the valve just enough to let the engine run.

Another way to test is carb right side up as installed on engine. Fill carb bowl and fuel line with fuel. Then attach your pressure tester at 7psi ONLY. See what you have.

SOLVED!!!! Put the carb back on, new plugs, new air filter. Runs perfect. Carb must of has something it it somewhere! The jets were spotless when I took it apart and cleaned it the 1st time. Very surprised it was the carb as new as it is. Thanks for all the help!

dawgslife5436 said:

SOLVED!!!! Put the carb back on, new plugs, new air filter. Runs perfect. Carb must of has something it it somewhere! The jets were spotless when I took it apart and cleaned it the 1st time. Very surprised it was the carb as new as it is. Thanks for all the help!

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Guessing you might have an intermittent carb needle and seat issue. I would replace with Briggs parts and call it a day. Not much money either.

Hope she stays running good for you.