Small Engines (Lawn Mowers, etc.): Murray 5 hp lawnmower problem, timing light, fuel cap

Question
Mower starts, runs rough. Moving governor, mower will idle smoothly, but when  moving governor for a faster speed, it begins to labor, missing and struggling to attain a faster smooth speed. I clean the carb, no help, replaced carb and still have the problem. What would you suggest I do next?

Answer
If you are sure the problem isn't related to the carb, you need to check the fuel tank vent.  Try loosening off the fuel cap and see if the problem still happens.  If this solves the problem, replace the fuel cap (vent is usually in the cap).  If not, you may have an ignition problem at higher RPM causing this.  You can use a battery powered timing light hooked to the spark plug lead, point the light at something dark and visually verify the strobe from the timing light doesn't show an ignition miss (you will know exactly what I mean if you have a miss).  If neither of these are the problem, let me know exactly what you found and I'll try to help further.  Hope this helps.