As mentioned in several other posts, FUEL is the biggest problem. I am in charge of all equipment maintenance for US Lawns of Lakeland, a complete property maintenance company, so I'm maintaining every thing from two cycle trimmers, edgers, blowers, weed eaters, chain saws to ride on spreaders, Dixie Choppers, Ex Mark, Scagg's Lesco and just about every type of truck. The biggest problem with *ALL* of these is the effect of the ethanol fuel.
The symptoms...hard starting, rough running, stalling, low power, bogging at WOT, especially on the two cycle. It all comes back to the fuel, emptying the tank and running the engine until the fuel is gone is the best protection.
One thing you have to keep in mind, the fuel we get from the gas stations is not fresh, when it is shipped it usually spends, some times, two to three months in storage tanks before ever being shipped to the stations. The other thing is, when you pump gas the first five to ten seconds of pumping, you're getting what the last person pumped, if it was the 93, more power to you, but in most cases, now days, it's most likely going to be the 87 or 89, plus the time the fuel spends in the can during storage. I have seen the cylinder broken completely off the block on two cycle equipment due to bad gas causing detonation just trying to start the engine. This stuff causes the the fuel feed and return lines to become hard and brittle, it also causes the diaphragm to become stiff and unpliable, I rebuild carbs on a regular bases.
On mowers, after sitting, drain and replace fuel, clean plug and air filter and oil changes are crucial, over time fuel blow by will cause the oil to become as thin as water, crank case pressure will cause it to blow by the piston rings and building up in the combustion chamber, which causes hard starting and can build to the point where it will seem like the engine is seized up, the best remedy for this is to pull the plug and turn over the engine several time, in extreme cases the fuel oil mixture will spurt out like a fountain, drain and replace oil.
Another thing that happens is the contact points between the ignition coil and the magnets on the fly wheel become rusty causing poor contact, a little light sanding with 200 grit paper will fix this problem. In actuality the fuel, carburation and ignition systems on mowers and two cycle equipment are the same as what was used fourty years ago, simple, reliable and it works. Hard starting is always a simple problem, fuel and spark.
