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Old 08-24-2010, 12:32 AM   #1
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I'm having trouble with my 4.5 hp lawnmower.. When I pull the starter rope it stops abruptly and nearly snatches my arm out of socket. If I pull the spark plug to relieve compression it pulls smooth. I've already bought a new mower but if this one can be revived I'll give it to my son. Any ideas would be greatly appreciated.
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Old 08-24-2010, 03:02 AM   #2
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Sounds like an ignition issue. Try pulling with just the spark plug wire disconnected (grounded if possible). If you no longer get the kick, the spark plug is firing at the wrong time. If you still get the kick, the valves are out of adjustment. Either fix is going to require some disassembly.
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Old 08-24-2010, 07:02 AM   #3
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Hope the motor hasn't seized up.
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Old 08-24-2010, 10:22 AM   #4
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Quote:
Originally Posted by daqq View Post
Sounds like an ignition issue. Try pulling with just the spark plug wire disconnected (grounded if possible). If you no longer get the kick, the spark plug is firing at the wrong time. If you still get the kick, the valves are out of adjustment. Either fix is going to require some disassembly.
Thanks for the feeback.. There is no kick with the plug wire disconnected! Would this mean the flywheel has slipped or something? If so, is the flywheel keyed?
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Old 08-24-2010, 12:13 PM   #5
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Not sure if that is your problem, but if you have to take the flywheel off this helped me. Sounded worse than what is was. Didn't take long at all.



How to Replace the Flywheel Key on a Briggs & Stratton | eHow.com

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Old 08-24-2010, 12:43 PM   #6
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Thanks again forum members. I don't claim to be a mechanic and I don't know what else could cause the plug to fire when it's not supposed to. If I'm not mistaken there's no points involved on a simple single cylinder. The magnetic part of the flywheel activates the spark through a coil or something. Please correct me if I'm wrong. What else could cause the misfire? Without any other feedback I'll pull the flywheel and look for a sheared key.
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Old 08-24-2010, 01:05 PM   #7
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That is exactly right about the magnet on the flywheel. First thing to check is the key that locates the flywheel on the shaft. Sounds like a timing issue if it stops when you disconnect the plug wire. There are no points unless it's 25 or so years old. The electronic ignition is located in the magneto. You'll have to pull the starter ratchet and remove the flywheel to change the key.
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Old 08-24-2010, 04:43 PM   #8
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Thanks again.. did have a sheared key. It's just finding the right one now. Went to the Tool Shack in Gulf Breeze who said they have them. He came out with two. One was too big and the other too small. Said the small one was the right size. I still had to modify it in to a half moon shape with the bench grinder. The mower started on the first pull ran for about 30 seconds and died. Sure enough the modified incorrect one sheared as well. At least I know what the problem is now. Thanks for everyones help.
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Old 08-24-2010, 05:11 PM   #9
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Glad to hear you at least found out what's wrong. I guess it's true that knowing whats wrong is only half the battle. Thanks for the end result, it'll probably help someone else.

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Old 09-02-2010, 04:42 PM   #10
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A1 small engine up 29 will have the right key
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