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I just bought a used lawnmower with a 4.5 Hp Briggs and Stratton engine. It doesn't really run properly. It starts fine, but then runs sporadically. The plug is the one that came with it and I can't find the proper gap or right plug specification. It's almost like there is a carburetor issue as it idles up and down. What can I do about it?
By MikefromGA from Raleigh, NC
The gap should be around .030. Replace the air filter and give it a tune up.
This is a page about diagnosing a mower with a Briggs and Stratton engine that won't start. Before you take your mower to a repair shop, here are some possibilities to look into. Diagnosing the issue yourself can save you time and money, so its worth a try.
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My Briggs and Stratton Weedeater push mower is not starting. It seems to not get any spark and I have a new spark plug, new gas, and oil.
Please help. My lawn is growing wild.
By Linda from Fayetteville, NC
Sounds like problems with the fly wheel, you would have to pull the fly wheel off and put a new key on it. If you do some searches online you can find the instructions on how to do this.
(assuming you are the same person who hit something with the mower, or ran something over), even if you aren't the same person, it does sound like the fly wheel. Hope this helps. (05/04/2010)
Try adding seafoam to the gas. (05/04/2010)
Check the key on the flywheel, if it's rotating freely and shaft does not move the key is broken. If it is still good then the gap between the magneto and the flywheel gap is off. Or it it is covered in rust, just clean with a wire brush, rest gap and key and your good to go. If still no spark the magneto might be bad. (06/16/2010)
By Daniel Garza
I have a 4.5 Hp Briggs and Stratton Engine on my lawn mower. It's only 2 years old, but has never really run properly. It starts fine, but then runs sporadically. It's almost like there is a carburetor issue as it idles up and down. What can I do about it?
Ham Bone from Denver, CO
Sounds like the same trouble we had with ours, we thought it was everything from carburetor trouble to the primer bulb. When we gave up and went to our local garden tractor repair shop they listened to our trouble said I know exactly what you need. Walked over and picked up a $5.00 carburetor gasket and said you may have to replace this every year or so. Now it runs just fine. Sounds like this is a common problem. Hope that this will help you. (05/23/2008)
By Michelle P
I have 17.5 Briggs and Stratton. I hit something while mowing the lawn and now when you start the engine oil mixed with gas pours into the carburetor. It does start, it runs for 5 seconds then trouble starts. It looks like it's coming from rubber tube connected to the side of engine that connects to the base that mounts to the carburetor. It is a riding lawn mower, if that matters. Please help I'm in a bind. Can it be the shear key?
By dudemay from LA