Just to be fair -- the ZDZ40 RE--will on a JMB muffler turn 21x8 Mejzlic at 7200- and on pipe with 22x8 Bambula wood - at 6700 easily and that is one heavy load .
two different engines - also we have tried different carbs to reduce low end vibes --and it works -
On a good in cowl muffler on a third engine - a 22x8 Bambula at mid 6000-
Other 40's I have run were pretty much in same ballpark-
The carbs have been on some frankly a problem PITA --but it has always been--the carb -- not the engine .
The 26 Evolution is just plain ol one of the best really small gassers I have ever seen - mine likes to run over 8500/ aprox on the ground for all around best power and that ends up 9500 in the air - on the current Funtana - on the Showtime this setup was simply ballistic I have use the supplied pipe and header same results -
anyone who gets poor performance with this engine either has done something wrong - or somehow damaged the engine .