[QUOTE=Rhansen]I've read this before when searching but no one says why the 1406 is not recommended. Jetting/squirters etc can all be changed, and the throttle bores are the same - so why not the 1406? Fuel passages different or something?
The comment the tech made to me was the 1406 would not "keep up" with the manifold. He did not explain and I did not ask him to elaborate at the time. But seeing that the RPM Air Gap is supposed to perform up through 6500 rpm I would think the carb might be somewhat stretched out to feed the engine on the top end and also built to run lean as well. The recommended 1405 is the same cfm rating so it doesn't look like a VE constraint. Sorry I can't shed more light on the issue.