My 3.5 hp B&S walk behind mower was surging. I cleaned fuel cap & carb and that did not help. I then chaned the carb and that did not help. I then changed the magneto and that did not help. So as a last resort I pulled the flywheel and changed the alum key and now the mower will not start. I now have no idea where to look. I need MAJOR help
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Walk behind surging and now won't start.
- Thread starter dmole
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Export threadThe original problem was "surging" up and down in rpm called 'hunting' and that is caused by the engine not getting enough fuel. Some of these engines are "constant speed" and have no speed adjustment and many don't have mixture adjustments either. Carburetors made out of plastic! The older ones(Non-Plastic) did have adjustments , in which case I turned the mixture screw counter-clockwise about a 1/16 turn to enrichen it and see if that helped any. If improved I'd go about the same turn again. Once it levels out then stop. As for the not starting, I assume you put the coil and key back in the right positions. The coil has to be gapped properly to generate the spark. It is possible you may have gotten the kill wire going to the coil grounded out somehow. Pull the kill wire clip going to the coil and then crank the engine over and see if it gets spark. If so, then you've got a ground someplace from the coil to the kill switch. I don't see how putting the new flywheel key in would make a difference. When you check the flywheel again make sure the slots on the crankshaft and the flywheel align EXACTLY as that is what keeps it in time. I have seen new keys put in and the engine kick back and shear one or crimp it and cause problems.
1- Recheck the coil gap. You can loosen the coil, move it back, snug the 2 bolts, put 3 sheets of notebook paper between the coil and the flywheel magnet, loosen the coil and allow the coil to be pulled against the magnet, and tighten the coil bolts. 3 sheets of writing paper is about .009 - .010". This gap will work fine.
2- Use a NEW plug. Connect the plug wire and ground the threads of the plug to the head, and pull the rope. You are looking for a spark.
3- No spark, either a bad coil or a kill wire grounded. Check to be sure the kill cable, its the cable that you hold down to start and to mow, has an air gap when it is fully pulled down. Check by looking at the cable being pulled and right near the carb.. There will be a small gap when the cable moves and creates an air gap where the kill wire from the coil is connected. No gap, no spark.
4- Got a spark? Shoot a shot of quick start fluid in the carb, pull the rope. If the mower starts, and I am 99.9% sure it will fire up, and then dies in a couple seconds, you have a fuel supply issue.
2- Use a NEW plug. Connect the plug wire and ground the threads of the plug to the head, and pull the rope. You are looking for a spark.
3- No spark, either a bad coil or a kill wire grounded. Check to be sure the kill cable, its the cable that you hold down to start and to mow, has an air gap when it is fully pulled down. Check by looking at the cable being pulled and right near the carb.. There will be a small gap when the cable moves and creates an air gap where the kill wire from the coil is connected. No gap, no spark.
4- Got a spark? Shoot a shot of quick start fluid in the carb, pull the rope. If the mower starts, and I am 99.9% sure it will fire up, and then dies in a couple seconds, you have a fuel supply issue.