I started to have trouble stating my engine. It is a Tanaka 32 with 2500 miles, and it would usually start on the first try. But several times in a row it took many tries and then did not start at all, I replaced the spark plug and it then started just fine. Should a spark plug fail after only 2500 miles? Its appearance was a light brown/rust like color. No oil on it. However, with the new plug I lost 2 mph in speed and the engine was louder. Is that normal? After about 200 miles, I have regained 1 mph and the engine has quieted down. Is that normal for breaking in a new plug?