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Location: East of Seattle since 1992, 615' Elevation, Zone 8b - originally from SF Bay Area
44,570 posts, read 81,147,605 times
Reputation: 57793
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While I have done a lot of my own repairs on cars and small engine for many years this one has me stumped. I have a Sears riding mower, model 502.255070, with 10 HP Tecumseh electric start. Last weekend it ran just fine. Today it cranks just fine (until I ran out the battery) but will not fire even a little.
The gas is full, oil fresh and full, the fuel shutoff is on, there is gas in the bowl, and good spark. The fuse is good, and I had it in neutral, mow lever off, and was sitting on the seat. When I pull the plug, it smells of gas and looks wet. I held the plug to ground and had my wife crank it and got a nice spark (and shock). Are there any other safety sensors/switches that I may have missed, or any other ideas?
Possible bad gas. but sounds like it is/was flooded with the spark plug being wet. you can burn the fuel off the plug with a lighter or match but don't get burned in the process. Or replace it with a new one. Sounds like all is in order......
Best of luck
I'd also first try removing spark plug and put a little lighter fluid directly in cylinder then replacing. If it doesn't fire then you likely have firing problem.
While I have done a lot of my own repairs on cars and small engine for many years this one has me stumped. I have a Sears riding mower, model 502.255070, with 10 HP Tecumseh electric start. Last weekend it ran just fine. Today it cranks just fine (until I ran out the battery) but will not fire even a little.
The gas is full, oil fresh and full, the fuel shutoff is on, there is gas in the bowl, and good spark. The fuse is good, and I had it in neutral, mow lever off, and was sitting on the seat. When I pull the plug, it smells of gas and looks wet. I held the plug to ground and had my wife crank it and got a nice spark (and shock). Are there any other safety sensors/switches that I may have missed, or any other ideas?
I just want to clear up one point: Did your wife do anything different than you did? Did she make sure the tractor was in neutral and did she completely hold down the brake/clutch pedal? I presume that she sat on the mower while you were doing the old shock test? Is it possible that she depressed the pedal harder than you did? Many tractors have all kinds of safety switches. Some even have thermal and low oil cutoff switches. I am just surprised that you cranked so long until your battery went dead and the engine did not even attempt to fire - but you had spark when you tested the spark.
It could be bad fuel or water in the fuel, a bad spark plug, carburetor way out of adjustment or you never took off the choke? However; I would still go with a safety switch first - check your oil (just in case).
Let us know what was the matter when you find out. Good luck!
Location: East of Seattle since 1992, 615' Elevation, Zone 8b - originally from SF Bay Area
44,570 posts, read 81,147,605 times
Reputation: 57793
Yes, I made sure both of us pushed the pedal all the way down, Same with the switch that won't let it crank when the mow lever is on. The oil is full. My first thought was oil level since I have run into that with my generator before. When no one is on the set it won't crank, so the switch is OK. The fuel should be OK, since I filled it last week before mowing and it's still 3/4 full. I tried bypassing the seat switch and same result. I also tried squirting fuel into the head through the spark plug hole with no change, so the choke is something to check. The cable moves at the lever but may have fallen off at the carb end, I have to take off the whole air filter assembly to see.I would think that it would still fire but not stay running with the choke stuck closed, but I'll see later. The fuel filter is new (June) and the bowl is full so it has fuel to the carb. I think I'll go get a new plug anyway.
Location: Democratic Peoples Republic of Redneckistan
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Not sure if your 10hp has the type of carb that has the wire runnning to the bottom of the carb to shut the fuel off,but if it does you can check that...I have a 20hp that failed to start after doing good the last time I used it..I tried everything like you have and finally decided to pull and clean the carb...when I got the air cleaner housing off I noticed the wire had somehow came disconnected..hooked it back up and 5 seconds later it was running like a swiss watch again..hope this helps as I know how aggravating that crap can be.
While I have done a lot of my own repairs on cars and small engine for many years this one has me stumped. I have a Sears riding mower, model 502.255070, with 10 HP Tecumseh electric start. Last weekend it ran just fine. Today it cranks just fine (until I ran out the battery) but will not fire even a little.
The gas is full, oil fresh and full, the fuel shutoff is on, there is gas in the bowl, and good spark. The fuse is good, and I had it in neutral, mow lever off, and was sitting on the seat. When I pull the plug, it smells of gas and looks wet. I held the plug to ground and had my wife crank it and got a nice spark (and shock). Are there any other safety sensors/switches that I may have missed, or any other ideas?
You have a bad plug.
When the plug fouls, it accumulates dirt/oil/fuel on the insulator tip. The dirty insulator tip then conducts the spark to ground (through the threads) instead of making it jump the gap. Many people overlook the insulator when they look at the plug.
Replace the plug, and on the off chance that the dirty air cleaner actually caused the problem by choking off air, clean it, too.
Yes, I made sure both of us pushed the pedal all the way down, Same with the switch that won't let it crank when the mow lever is on. The oil is full. My first thought was oil level since I have run into that with my generator before. When no one is on the set it won't crank, so the switch is OK. The fuel should be OK, since I filled it last week before mowing and it's still 3/4 full. I tried bypassing the seat switch and same result. I also tried squirting fuel into the head through the spark plug hole with no change, so the choke is something to check. The cable moves at the lever but may have fallen off at the carb end, I have to take off the whole air filter assembly to see.I would think that it would still fire but not stay running with the choke stuck closed, but I'll see later. The fuel filter is new (June) and the bowl is full so it has fuel to the carb. I think I'll go get a new plug anyway.
If it was flooded; you could simply let it sit or take the sparkplug out let it dry out. Just a little moisture could cause these problems. Are you getting any engine wheezing from stuck valves? When I had my shop I did have some bad spark plugs right out of the box - but that was years ago and I really don't suspect that in your case.
If it was a safety switch you would not have fire or even be able to turn over the motor. I'm kind of puzzled.
Talking about getting a shock. Years ago I was adjusting the carburetor on a snow thrower. I leaned over the unit and touched the tip of my nose to the sparkplug. It put me right back on my butt! It is bad enough getting it on your arm of fingers - don't ever try it on the tip of your nose!
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Is it possible that she depressed the pedal harder than you did? Many tractors have all kinds of safety switches. Some even have thermal and low oil cutoff switches. I am just surprised that you cranked so long until your battery went dead and the engine did not even attempt to fire - but you had spark when you tested the spark. 
