Small Engines (Lawn Mowers, etc.): my strimmer, fuel vapors, grass clippings

Question
my strimmer wont work right. 1st thing is it will idel fine for a few secs then idel rough and cut out even does it when the thing is hot. 2nd thing is if i stop it for a few seconds to have a drink or something when i come back to finnish off the job its hard to start.

Answer
Toby

There can be numerous reasons for the engine to quit running when it gets up to operating temperature.. expansion of metal parts where bolts/screws aren't tight enough, breakdown of the condenser for the ignition points (if equipped), or a possibility of a crack somewhere. An overall inspection of the tightness of fasteners would be a good place to start.


If the miss is a miss, the problem probably has to do with ignition or the fuel mixture. Check the tightness of the carburetor mounting bolts and where the intake manifold/air-fuel mix tube fastens to the engine block.

If instead, the miss is popping through the exhaust, this might be caused by a bad exhaust valve or valve seat.

If there is puffing or popping near the engine head, the head bolts might not be tight.

If the engine spins over too freely when it's hot.. indicating much lower compression, check the torque of the head bolts.. if they were loose, the engine should now restart.

If it won't restart until it's cooled down, the exhaust valve (and/or valve seat) may be the problem. If you can remove and disassemble the engine yourself, this isn't expensive to have corrected. If not, the shop labor for tear-down and reassembly will be fairly costly. A common reason for exhaust valve failure is that grass clippings become embedded in the cooling fins around the exhaust port area.

If the engine is just failing to fire the spark plug when it's hot, there's a good chance that it's time to change the (points and) condenser. This can usually be confirmed by quickly removing the spark plug after it quits running, and grounding the sparkplug base securely to the engine (away from fuel vapors).. then spin the engine to see if there is a hot blue spark with an audible snap, snap noise.