# Lawn tractor carb problem



## begreen (Aug 22, 2010)

We've got a 4 year old Craftsman lawn tractor with an 18hp CV492 Kohler motor. It's been running great up until today. Suddenly it is cutting out, like fuel starvation when not on the level. On the level or slight incline it still runs fine. But as soon as I am on a hill, either sideways or heading uphill, it starts cutting out. 

I don't know much about carburetion on these motors and unfortunately the Sears documentation on the engine is weak. Are there some good sites or information locations for carburetor repair? I am hesitant to start tinkering without some good detailed diagrams and guidance.


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## semipro (Aug 23, 2010)

Tear into it but check your fuel supply to the carb first (check filter then pump).  Look for water in the filter too.  If you have plenty of fuel getting to the carb you'll need to disassemble the carb.  The carb is likely to be really simple and I can tell from your posts that you possess the common sense needed to figure it out.  I don't know that particular carb but I'm betting its either a fuel level issue (float, needle, seat) or water in the fuel bowl.  The float, needle and seat work like the valve in a toilet to maintain a certain fluid level.  Water in the system can cause some crazy problems.  If for some reason you suspect water got into the system you can add some gas dry, basically ethanol or methanol to the fuel tank.  

Oh yeah, check you engine oil level first.  You mower may have a kill switch activated by low oil pressure.  If the oil is low enough the incline will starve the pump and result in a pressure drop.  

Good luck.


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## begreen (Aug 23, 2010)

Pump? This appears to be gravity fed from the tank. The filter seems fine. Good steady flow through it. By the way it is affected according to tilt, I suspect the float/needle valve, but not sure. Water in the gas seems unlikely. I'm about halfway down on a 5 gallon can and it hasn't rained here in a month. Did check the oil level, it is right up to snuff. But that is a good suggestion and fits with the hill problem. I may add a little just for yucks to see if that affects anything because it runs just fine on the level.


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## benjamin (Aug 23, 2010)

I don't know anything about Kohlers, but most small engine carbs are pretty simple.  Just take the plug off the bottom of the float bowl, usually 7/16", that's usually some kind of drilled jet, check that to see if it's clean, and pull the bowl off and check if there's any crud in there.  On a bigger engine like this it's usually not as bad as the small ones that have tighter tolerances and go through a lot less gas.  

I have no idea if the carb is your problem, but that's how I'd check it if that's what you suspect.  Just make sure to be careful if you mess with the float and the spring that holds the needle in, PITA  to get back together.  

I know old gas, ie gas that's gotten to hot in storage for even a short time, will make two cycles run terribly, it's a stretch, but it could be causing this.


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## Captain Hornet (Aug 23, 2010)

My Craftsman was doing the same thing.  It was really noticeable when there was a half tank  or less fuel aboard.  Fix was a new fuel filter.  They are inline ,usually hanging on the side of the engine.  I also had problems with the weight on seat switch that is under the drivers seat.  I finely got rid of the switch, bypassed it, but I don't remember if it was a open or jumpered together.  Good little tractor mower when you finely get the bugs worked out.  David


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## begreen (Aug 23, 2010)

The tractor has been great, this is the first serious issue with it. I just checked the schematic and there is no low oil cut off. I switched the filter out in spite of good gas flow through the old one. That doesn't seem to be the issue. I went out and tried again and now the tractor won't run at all. Either there is a screen in the carb that is plugged, a stuck float or I am wondering about the fuel cutoff solenoid. It's what stops the mower if the seat is unoccupied, etc. If this fails, then all bets are off. I need to get a meter on it to see if it is getting voltage. If so, it is prime suspect. If not, then I need to find the errant switch or perhaps it's the operator presence relay that has failed. Such fun.


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## boatboy63 (Aug 23, 2010)

I am a certified outboard marine tech and have owned my own part time business at home doing this and also worked for a $tealership for a few years. Contrary to what many mechanics do with customers, I have always tried to give my customer a simple suggestion to try before bringing a motor to me for a simple carb issue. I will normally tell them the little trick I am going to share with you and if that doesn't take care of the problem, then I tell them to bring it in. Get a can of concentrated fuel injector cleaner just like what you would buy for your car. Most of the time, a bottle of this will do anywhere from 15-20 gallons of fuel. I tell the customer to just mix a tank at about twice what it calls for and try it. Typically, this would be around an ounce or so per gallon. Mix this in with a tank of fuel and run the engine as you normally would. I have always used the injector cleaner instead of regular carb cleaner, as I feel it is refined a step further. 

Another thing to look for is to keep an eye on your oil level carefully. If you notice the oil level starts rising, don't run the mower anymore. What is probably going on is that your inlet needle/float assembly is stuck open. When this happens, the fuel continues to gravity feed into the carb and the float will not shut it off when full. The fuel level will continue to rise and eventually, it will run out from the "throat" of the carb and into the cylinder/s. When this happens and the engine is not running, it will drain into the cylinder on top of the piston. Since you have a small ring end gap in the piston rings, the fuel will find it's way thru the gap and drain down into the oil. As this happens, it will thin the oil down and can actually wash down the bearings, as the oil has thinned out too much to lubricate.  

This was a common problem at one of the $tealerships I worked at as they sold 4 wheelers and over half of the ones we sold had this common problem. We would typically have 4-wheelers stacked in crates for 4-6 months at a time before they were ever uncrated. When we did uncrate them, they ran fine for a day or 2 then developed this problem. I called the manufacturer and discussed the problem. Come to find out, they would start a new model year somewhere around March and not release them until August or Sept. At the time they were assembled at the manufacturer, they would put around a quart of gas in them, test fire them for 1 minute and then shut them off. Let's say this happens in March and we didn't uncrate them until November. This is nearly 9 months that the fuel has been in the carb and has began varnishing by then. As the fuel evaporated from the carb in the months, the varnish would happen faster and start causing problems. Because of this, I either added injector cleaner to them after starting them up, or the ones that already had signs of problems had a carb cleaning done before ever being sold.

What I would suggest with any lawn mower, tiller, chain saw, outboard, jetski, or anything that is going to be stored for several months...Add fuel stabilizer to the fuel tank and run the motor for at least 10-15 minutes before storing it so the stabilizer can mix with the fuel and be distributed thru the engine. Don't do the old "grandfather trick" that has been passed down for years. This involves shutting the fuel valve off and letting the motor run until it runs out of fuel. Truth of the matter...you didn't run it out of fuel. You ran it down so the fuel level was so low (lean), it could not run anymore. The reduced amount of fuel in the float bowl will now evaporate faster, leaving varnish deposits in the process. When this happens with a 2 stroke engine, you also managed to rob the internals of your engine of the oil that lubricates the engine and protects it from rust thru it's winter storage. 

Last tip...Trash that metal fuel storage tank and buy plastic instead. The metal will cause condensation at the bottom of the tank due to hot/cold changing temps from day to night. This condensation can cause the tank to rust and contaminate your fuel system. Fuel also tends to varnish faster in a metal tank than what it does in plastic. The plastic also has less condensation as plastic is a better insulator than metal.


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## begreen (Aug 23, 2010)

The tractor has been great, this is the first serious issue with it. It was last run just a couple weeks ago and was fine. The oil level has been constant, no issues there that I can find. I just checked the schematic and there is no low oil cut off. I switched the fuel filter out in spite of good gas flow through the old one. That doesn't seem to be the issue. I went out and tried again and now the tractor won't run at all. Either there is a screen in the carb that is plugged, a stuck float or I am wondering about the fuel cutoff solenoid. It's what stops the mower if the seat is unoccupied, etc. If this fails, then all bets are off. I need to get a meter on it to see if it is getting voltage. If it is, this may be the prime suspect. If not, then I need to find the errant switch or perhaps it's the operator presence relay that has failed. Such fun.


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## benjamin (Aug 23, 2010)

Congratulations!  now that it won't start it should be easy to find something wrong.  

Hope you don't spend  an hour finding out that the blades aren't all the way up or it's not in neutral, hate it when that happens.


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## boatboy63 (Aug 23, 2010)

BeGreen said:
			
		

> Either there is a screen in the carb that is plugged, a stuck float or I am wondering about the fuel cutoff solenoid. It's what stops the mower if the seat is unoccupied, etc. If this fails, then all bets are off. I need to get a meter on it to see if it is getting voltage. If it is, this may be the prime suspect. If not, then I need to find the errant switch or perhaps it's the operator presence relay that has failed. Such fun.


I am not sure how your mower is set up, but are you sure it is a fuel cutoff solenoid? Most of the seat switches only have 2 wires underneath them and you can simply jumper over the 2 wires to bypass it. At least with mine, that is how you do it. I can't see them spending the money on an actual solenoid when they can simply break a circuit on the ignition alot cheaper. Instead of checking voltage on the seat, I would disconnect both wires and check continuity across the switch. Typically, if nobody is on it, the circuit would be open, but when you sit down, it closes the switch, and completes the circuit. Also, KISS...have you checked the spark plug?


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## begreen (Aug 23, 2010)

I went on the Walbro carb site. It looks like the solenoid is an anti-backfire device for when the motor is shut off. It cuts the fuel off to prevent backfiring. The voltage check I need to do is at the solenoid, not at the seat. The seat switch doesn't engage unless the attachment (mower) is engaged. This problem is before that circuit.


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## festerw (Aug 23, 2010)

1st I'd give it some starting fluid if it starts it's a fuel issue if it doesn't it's an electrical issue.

If it's electrical pull the white kill switch wire off the ignition module and see if it starts, if it does you've got a short somewhere in the safety switch wiring.  You can run it without the white wire connected, just be aware that none of the safety systems will work until you find the short however it will still shut down via the key switch.


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## Jags (Aug 23, 2010)

BG - I think fester is on to something.  You can cut your troubleshooting in half by doing the ether trick.

Give the carb a shot of either - try to start mower.  If it pops or briefly runs, it is a fuel/carb issue.  If it does not pop or run, you are probably on the right path of electrical/ignition breaks.


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## Lucky Phil (Aug 23, 2010)

I bought a used JD tractor last year, and after a while it would stop on the hilly part of my yard.  I would disconnect the fuel line and blow through it, and it would start and run again.  I even put a filter inline, but it kept doing it.  The breather hole in the fuel tank cap had gotten plugged, and it was pulling vacuum on the tank.  It had to be a coincidence that it always died on the hilly part.  No problems since.


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## benjamin (Aug 23, 2010)

boatboy63 said:
			
		

> BeGreen said:
> 
> 
> 
> ...



I goofed in my earlier post,  on riding mowers the plug I was talking about is usually a shut off solenoid that also holds the little aluminum fuel bowl in place.  Pretty easy to check with the tricks mentioned above: starting fluid or disconnecting the ignition wire-most ignition systems are a magneto that is shut off by grounding it through the seat, switch, low oil switch etc, disconnect the wire and it should have spark.


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## begreen (Aug 23, 2010)

Good tips all, thanks. As of last night the mower would not start at all. It was getting late so I decided to sleep on it. This morning I went out and checked and ding ding ding, I think we may have a winner! On close inspection I did find bit of brown gunk in the tiny fuel cap vent hole. Yesterday I missed this because I had the fuel cap off when I checked the fuel filter. Just now I pulled the cap and she started right up. I only ran it for about 5 minutes, but it went up and downhill without complaint. I'll give it a better test, with the fuel cap vent hole cleared, later today. Lucky Phil, looks like I owe you a beer! Boy do I like simple fixes.


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## Jags (Aug 23, 2010)

Whoo hooo!  Now when are ya gonna drop over and mow mine?  I'm tired of it.  It never quit growing all year.  Dang monsoons.


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## semipro (Aug 24, 2010)

BeGreen said:
			
		

> Good tips all, thanks. As of last night the mower would not start at all. It was getting late so I decided to sleep on it. This morning I went out and checked and ding ding ding, I think we may have a winner! On close inspection I did find bit of brown gunk in the tiny fuel cap vent hole. Yesterday I missed this because I had the fuel cap off when I checked the fuel filter. Just now I pulled the cap and she started right up. I only ran it for about 5 minutes, but it went up and downhill without complaint. I'll give it a better test, with the fuel cap vent hole cleared, later today. Lucky Phil, looks like I owe you a beer! Boy do I like simple fixes.



I've experienced the same problem (and fix) before but it never coincided with operating on a slope.  Glad you got her fixed.


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## begreen (Aug 24, 2010)

I think the whole slope thing was a red herring. Mostly the lawnmower was running because I would pull the fuel cap and check for any water or junk in the gas tank. I cleared out the blockage in the vent and now she is running great! Nothing much to mow here, just weeds until we get fall rains. But it's good to know it's ready. I use the mower to pick up and mulch leaves too, so I want it to be working well in fall.


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