When my 450 is idleing it will knock or clunk every once and a while. What is causeing it to miss like this? I just changed the spark plug.

 

Is the idle speed too low? Its supposed to be 1300 to 1500 rpm.

 

how do u check the idle without a tachometer. Also i just had my valves ajusted for the first time after 7,000 miles!

 

If you dont have a tach, then youll have to guess. There are a few inductive type tach/hourmeters out there, for about 40 bucks new, but if you dont have one, try bumping up the rpm a bit at a time, and see if the noise goes away. If it wants to creep forward in first, or it gets hard to shift into reverse or first, then its too high. The centrifical clutch is all in at about 1800 prm.
I assume youve checked the oil level (with out screwing the dipstick in), and the proper viscosity oil is in there.