John Deere GX 335 runs rough, excessive black smoke

[elmrfudd]

I have my mom’s JD GX 335, with a Kawasaki engine, 8100 hours, (FH601V-CS04, ENO FH601VB29323), and trying to troubleshoot the rough running and excessive black smoke pouring from the exhaust. My brother was mowing my mom’s yard, and after about 20 minutes of mowing, all of a sudden he encountered the black smoke, and the mower barely ran, so he put it away. Both spark plugs had electrodes that were completely covered with black soot. My first thought was that both coils usually don’t fail simultaneously, and each plug was spark-tested successfully. Once it’s running, at idle it runs just fine until I begin to throttle it up, then it struggles with the excessive rich-running symptoms, eventually choking off the engine until it quits. I did drain the fuel tank, which did have some water in it, and added fresh gas, to no avail. I did an ultrasonic cleaning on the carburetor, so I made sure all internal ports were clear, and used compressed air to remove cleaning solution. I welcome an suggestions as to what I can look for next that may cause the “choke and smoke” symptoms. And yes, the choke is wide open and working perfectly. All input is greatly appreciated! Thank you!

 

[Rivets]

Check your oil level and if it smells like gas. If so you have a carb flat needle that is not sealing properly. If not the problem I would be testing for blown head gaskets on both cylinders.

 

[hlw49]

Make sure the air filter is clean and the choke is working properly.

 

[elmrfudd]

Check your oil level and if it smells like gas. If so you have a carb flat needle that is not sealing properly. If not the problem I would be testing for blown head gaskets on both cylinders.

That was my suspicion when my brother explained the symptoms from the get-go, and I changed the oil anyway just in case that was the issue. Oil level then was just slightly over the full mark. I just checked the oil level, and it’s a little below the full mark, and just smells like pure oil, so I’m ruling out the leaky carb. I’ve seen the leaky needle/seat situation before, where the crankcase was way over the full mark, oil super-thinned out, and obvious gas smell coming out the filler tube. This is not the case here. I’ve also changed many blown head gaskets over the years, and there are none of the obvious symptoms of such, like the hissing sound or heavy blue smoke. I do have some shop experience, and have seen similar symptoms, but I suspect something deeper going on here. I don’t have a ton of experience with Kawasaki engines, so was wondering if this issue might be more common with the brand. Also, the air filter is not brand new, but reasonably clean. What my biggest question is, is why was it running great for my brother for twenty minutes, then all of a sudden it was like someone put it into full choke mode? Thanks for your input guys, and I really appreciate it!

 

[bertsmobile1]

probably crud stuck under the float needle
The dim witts in the EPA decided that the carb bole overflow / vent had to be internal so when the float bowl overfills the fuel flows out of the hole in the back of the carb and directly into the engine manifold giving you an effective main jet of .125" about 50 times the actual main jet size .

 

[elmrfudd]

Well, because of my suspicions that the gas was making its way into the oil, the first thing I did was remove the carburetor, strip it down, and put it in my ultrasonic cleaner for two hours at about 160 degrees. Needle and seat were extremely clean when done, so there’s no crud. I searched the web for a carburetor kit for this engine, with no success. Plenty of cheap aftermarket carbs out there, and found some OEM carbs for $300+. That’s an expensive part to put into an old mower to risk a possible hit and miss repair. The internal carb bowl overflow/vent does make sense regarding making the mixture super rich, but this mower will sit running at idle all day long, purring like a kitten, with not even a hint of black smoke. I would think with that much internal fuel in the carb/intake, it wouldn’t idle at all. So bertsmobile1, this could very well be a design flaw common to Kawasaki engines, in your opinion? I am open to an additional cleaning and new needle and seat if I can find a kit anywhere for this carb. Typically, after cleaning the carbs, I polish up the inside of the seat with a Q-Tip with a little toothpaste, and make sure there’s no lint or toothpaste left in the seat when I’m done. I’ve always had great success with that process. Thanks a bunch!

probably crud stuck under the float needle
The dim witts in the EPA decided that the carb bole overflow / vent had to be internal so when the float bowl overfills the fuel flows out of the hole in the back of the carb and directly into the engine manifold giving you an effective main jet of .125" about 50 times the actual main jet size .

 

[elmrfudd]

Well, because of my suspicions that the gas was making its way into the oil, the first thing I did was remove the carburetor, strip it down, and put it in my ultrasonic cleaner for two hours at about 160 degrees. Needle and seat were extremely clean when done, so there’s no crud. I searched the web for a carburetor kit for this engine, with no success. Plenty of cheap aftermarket carbs out there, and found some OEM carbs for $300+. That’s an expensive part to put into an old mower to risk a possible hit and miss repair. The internal carb bowl overflow/vent does make sense regarding making the mixture super rich, but this mower will sit running at idle all day long, purring like a kitten, with not even a hint of black smoke. I would think with that much internal fuel in the carb/intake, it wouldn’t idle at all. So bertsmobile1, this could very well be a design flaw common to Kawasaki engines, in your opinion? I am open to an additional cleaning and new needle and seat if I can find a kit anywhere for this carb. Typically, after cleaning the carbs, I polish up the inside of the seat with a Q-Tip with a little toothpaste, and make sure there’s no lint or toothpaste left in the seat when I’m done. I’ve always had great success with that process. Thanks a bunch!

I did find a 16030-7002 float needle valve on eBay for $23. It may or may not resolve the issue, but will hold off a bit until I get more input from the fine people on this forum. I have a full plate the next couple of weeks, which would allow a little time to gather some more comments. Again, I’m very appreciative of any insight that’s shared here. I really enjoy the knowledge and expertise I see on this forum.

 

[SeniorCitizen]

Can we eliminate a air filter problem by running it without the air filter for a few minutes ?

 

[elmrfudd]

Can we eliminate a air filter problem by running it without the air filter for a few minutes ?

Absolutely did that. As a matter of fact, right after reinstalling the carb after cleaning, I left the air filter off. Runs the same with or without the air filter.

 

[Tiger Small Engine]

I have my mom’s JD GX 335, with a Kawasaki engine, 8100 hours, (FH601V-CS04, ENO FH601VB29323), and trying to troubleshoot the rough running and excessive black smoke pouring from the exhaust. My brother was mowing my mom’s yard, and after about 20 minutes of mowing, all of a sudden he encountered the black smoke, and the mower barely ran, so he put it away. Both spark plugs had electrodes that were completely covered with black soot. My first thought was that both coils usually don’t fail simultaneously, and each plug was spark-tested successfully. Once it’s running, at idle it runs just fine until I begin to throttle it up, then it struggles with the excessive rich-running symptoms, eventually choking off the engine until it quits. I did drain the fuel tank, which did have some water in it, and added fresh gas, to no avail. I did an ultrasonic cleaning on the carburetor, so I made sure all internal ports were clear, and used compressed air to remove cleaning solution. I welcome a suggestions as to what I can look for next that may cause the “choke and smoke” symptoms. And yes, the choke is wide open and working perfectly. All input is greatly appreciated! Thank you!

A Kawasaki engine with 8100 hours on it should be in the Hall of Fame.