Small Engines (Lawn Mowers, etc.): Lawnmower not working, starter cord, valve problems

Question
Hi,

I am trying to start a small lawnmower that I got from a friend. First I did some maintenance work: cleaned the air filter, exchanged the oil, filled up the gas tank with new gas, replaced the spark plug with new one. Checked for spark and it is OK. The lawnmower just doesn't want to start easily. After pulling the starter cord for about 30 times, it started, and it worked for about 15 secs and it stopped. Once it worked for about 2 minutes. But when I want to restart it, the same story repeats again. I need another 30 pulls on the starter cord.

While trying to start it, the mower is backfiring every now and then, or some smoke is coming out from the exhaust, but the engine doesn't pick up power.

What else should I check?

Thanks,
Eugen

Answer
Hi Eugen,

It could be either:  A lack of fuel flow to the engine or low compression/valve problems.  Check the fuel flow by squirting fuel into the carb opening to try to keep it running.  Set the carb jets at:  Large, high speed mixture = 1 & 1/2 turns out.  Small, low speed mixture = 3/4 turn out.  If all that doesn't help, check the compression.

Let me know what you find.
Michael