This started happening towards the end of last Summer. My Stihl MS 250 chainsaw engine would bog down at the strangest times. I can’t say there was one time in particular, but I guess mostly when I put the saw under a load. When I started cutting with it, it would bog down and then I would stop and rev the engine. I would get it going again and the same thing would happen. Since it was the end of the season, I put the saw in the garage and hoped it would heal itself by Spring.
Well, I had to use the chainsaw the other day. Guess what? It had the same problem. My sharp senses told me what the problem was. For some reason, I knew I had to clean and re-gap the spark plug.
When I took the spark plug out of the engine, I took a glance at the gap. The side electrode and the center electrode seemed to be pretty close together. Since I had absolutely no idea what the gap is supposed to be for a Stihl MS250 chainsaw, I looked it up. I found out that the spark plug gap is supposed to be .020 or 0.5mm metric for the Stihl MS 250 Chainsaw. Yep, I was right. When I measured the gap with my spark plug gapper, it was too small.
Now, .020 gap is pretty tight. It’s actually the smallest size on my gapper. Good thing too. I re-gapped the spark plug and gave it a quick cleaning. Then, I reinstalled it in the chainsaw. I started it up and problem solved. I love it when a plan comes together. Now, the saw is nice and strong when I cut through wood.
PS – I wanted to write a quick note about trying to diagnose small engines. For some reason, people seem to love jumping into the fuel system. I am not sure why this is, when the easiest thing to check is the spark plug. Take out the plug, clean it, re-gap it and see how that works. Don’t take out the carburetor and rebuild it if you don’t need to. Most of the time, this is unnecessary.