Briggs & Stratton 6.5 HP engine (123K02-0181-E1) suddenly stopped while mowing and I could not get it re-started. I took the carburetor apart and cleaned it; replaced the spark plug, fuel line, changed oil and air filter. It started up for a few seconds and then stopped. I could not get it to start again. Does anyone have any idea as to what might be wrong? Thank you. Fvt