Mower start problen and questions

I have a Scott SP walk-behind mower with a 6.5 HP Tecumseh motor. The last time I used it (about 2 months ago) it seemed to run fine. Now it apparently makes no attempt to start (after priming it and after many pulls). In addition to this problem, while trying to start it the engine sometimes jerks the starting rope out of my hand (backfires?). Can anyone suggest what might be causing this and what to do about it? Thanks for any help. Art Replace deadspam with yahoo to reply.
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I have had similar occurrences, though I can't recall the specific cure. Here are some basic troubleshooting steps I usually take:
1) Since the mower does not want to run even when primed, I doubt that the carb is the main issue. If it was the carb, you would at least be able to run the mower by constantly pressing the prime button when it starts. This is good when the carb bowl has no gas in it.
2) Check the spark plug. What color is it? If it is black, then you have a fouling issue. Is it wet? If so, then it means that you are getting fuel, but no ignition. Clean the plug (or replace it). Make sure the plug is dry when replaced.
3) Check the air filter. Make sure that it is clean. A dirty filter will cause your mower to run rich and foul the plug. In extreme circumstances, a clean plug can foul in five or ten minutes.
4) If you are still not having any luck, remove the spark plug and reconnect it to the plug wire. Have the metal part of the plug touch the engine and pull the start cord. Do you see a spark? If yes, then you have a fuel delivery issue. If not, it could be the plug or the coil. Keep working with the above steps to see if it will run. If you still can't get it going, take it to a small-engine mechanic.

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Likely no spark or no fuel. You dont know if you are getting any fuel, remove air filter and squirt gas or starting fluid in. If nothing happens remove plug and ground it with the wire attached. If you get spark backfiring indicates a timing problem and a sheared flywheel key. If no spark you have to trace it back but start with a new plug. You need 3 things to run air, fuel and spark. No spark is plug, plug wire, coil -points-condensor, or coil ignition module. Or broken wire or stator. Backfire is timing , flywheel key. Maybe no compression also.
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Andrew,
Thanks for your comments and suggestions. When time permits, I will try to check out a few of those things. Meanwhile, do you (or does anyone else) have any opinions regarding the "backfiring" problem (where it jerks the rope out of my hand)? To me this suggests that the timing is off and that the spark is occurring too soon. Is this possibly correct -- and is there any cure for it? TIA again. Art
On Wed, 6 Apr 2005 16:23:29 -0400, "Andrew Neilson"

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Hit one rock and you can have a timing issue, common on some motors, a sheared key.
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Most likely Timing is not at issue. "Timing" is rarely an issue with 4-cycle engines. In fact there are really no timing adjustments. However there are Condensor point gaps that can be adjusted, and only after some serious hours of operation might the "Gaps" need adjustment. Altogether Comprised within The term- "Spark" is your issue. Change or clean your spark plug. A fouled spark plug would exhibit your precise condition.
Always good practice/preventative maintenance to change gas if old, using fresh clean gas and of course making sure to keep the air filter clean ALL of time..
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HI Art,
My first suspicion would be a broken flywheel key. I have the same engine in a Craftsman lawnmower and the damn thing breaks about two keys per season.
The key is an aluminum/pot metal sorry excuse, all you need to do is hit a rock, tree root etc, and it will partially shear, ergo engine timing is out.
There is no easy way to check short of pulling the top sheet metal, remove the recoil mechanism, remove flywheel nut and check alignment of flywheel to crankshaft. If not dead on, this may be your problem. WARNING, do not attempt to pry flywheel off, it will break, replacement worth more than mower! Use puller, apply heat to flywheel at crankshaft and the apply pressure. Fly wheel is mounted on taper.
Dave
Art Renkes wrote:

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