Is it time to make the change?
For God's sake, YES, it was time to change 40 years ago. And it hasn't been a mainstream competitive stunt engine for about *50* years. It was never a very good sport flying engine compared to many far easier-to-deal with alternatives.
People used it for sport flying because it was a pretty good competition engine for a brief period in the 50's and then (just like now, to a degree) people wanted to be able to brag about it even if it didn't make any difference for what they were trying to do. It's the same phenomenon that drives every sport flier and casual competitor into buying a "Joe Blow 40LA" instead of a stocker - it has nothing to do with the performance (which is usually much worse than stock), it has to do with wanting to tell their pals they have a "Joe Blow 40LA". This is the result of a second problem, where many competition aspirants can't grasp a similar situation, where ST46/60s and the like ALSO aren't mainstream competitive stunt engines, not for about *30* years.
At this point, we have people out there in the field torturing themselves for hours trying to get it to work, burp-quit-crash or shaking the airplane to bits in 3 flights, and then claiming how great the engine is.
These endless problems were potentially worth putting up with because when you got it working right, it was the best you could do in the mid-50's, and about even compared to most of your competitors through most of the 60s unless you were going to take on McFarland/Gialdini etc. Geiseke managed to hold on through most of the 70's but it eventually became too much even for him to overcome. A lot of the alternatives were not tremendously better in terms of performance but you don't have to be a lot better, just a little.
And don't move on to "McCoy/Enya/ST" because they are hardly any better for the most part. Enya now occasionally makes a modern-quality products on a very limited basis, ST makes more-or-less nothing too useful, and McCoy has been out of business far longer than Fox. OS is still in business but doesn't make CL engines, and if you convert a OS-35AX to CL, it has 5x the power you need to fly a Shoestring. Get a few year old 25LA or 20/25FP, convert it to CL with factory parts.
Note also that the same problem infests budding stunt competitors, still trying to hold on to the 80's to avoid anything "complicated" like a 40VF - which is ironically the EASIEST of all the recent generation to deal with. You bolt it together and go fly it, you need to know very little compared to the old days, it just goes and goes.
Expect my two cyber-stalkers to descend upon this thread to "correct" me and to claim they have advanced knowledge and that I am un-American, but I am trying to break you into the reality of the year 2017 instead of desperately hang on to 1956. Get a used 25LA from an RC guy, put in a stock venturi and a APC 9-4, and move on with your life.
Brett