Small Engines (Lawn Mowers, etc.): small mower repair, plug gap, metal tab

Question
Matt
I just put a tune up kit on my Craftsman mower.A 21" mulching,not self propelled. #917388360.
It still runs rough. The throttle can't be turned up and it runs at such low rpms and is not cutting very well.Though I also put a new blade on.
Any suggestions?
Thank you
Jeffrey

Answer
Hi Jeff,
  There should be a spring attached to the carburetor stem located at the top the carburetor. This stem operates the butterfly inside the carb. The spring runs from the plate on top of the stem to a metal tab. By bending this tab and putting more tension on the spring the rpms will increase. maximum safe speed for a mower is 3200 rpm but without a tachometer you will just have to play it by ear dont over do it with the speed its not safe and you could damage the engine.
  As far as it running rough... if you have a new plug in it first check the plug gap make sure the electrode wasnt smashed down. The factory gap is fine for the plug just make sure everything looks square. If the mower is skipping or sputterin you should check the flywheel key. you will need to remove the metal shroud over the top of the engine. Remove the starter cup on top of the flywheel. Where the crankshaft comes up through the center of the flywheel you will see a groove cut down one side of the crank. This groove should line up with a groove cut on the inside of the flywheel and a metal key is inserted to keep the flywheel positioned properly so the plug is firing at the correct time. The key will get bent from hitting objects with the blade and this throws the timing off. if the key needs to be replaced you will need to pry the flywheel up with a prybar or large screwdriver. Tapping on the top of the crankshaft with a rubber, fiberglass, or wood mallet helps loosen it, but be carefull not to damage the threads or you wont be able to get the nut back on. the nut should be torqued to 40 foot pounds when it goes back on. If you have the engine running at speed and the mower is no longer running rough but is vibrating badly then you may possibly have bent the crankshaft by hitting something. hope this helps you out let me know how it went.