This is my second season with a yr2000 Johnson 115. I did not change the impellar last year, but was thinking I should do so this year. I plan to buy a manual. But, in the meantime, any suggestions or tricks of the trade I should know about? I've never changed an impellar before on anything other than a 2.5hp small nissan engine. For a guy who basically just changes his own plugs and fogs the engine, but nothing too much more intense than that, is it a job that I should be able to do myself? Thx, sd