Contrary to what some may believe, Cox reed valve engines are some of the most reliable engines around - once you master the technique of starting them. I've found that many people accidentally flood them. When all else fails, read the owner's manual. I ran a Black Widow for years and never had it fail to start. The last plane it was on was a fairly hot pattern-type self design RC job. I ran it with a TD head for a bit of extra oomph. After a year or so, I noticed that it was losing compression when I hand-flipped it during priming. Turns out the higher compression was forcing the con-rod THROUGH the top of the piston - there was a hole in the piston, but not quite big enough to let the ball go all the way through. It STILL started on the first try every single time!