I've just added a new page entitled Advanced Tuning & Maintenance.  I'll be adding more details as I proceed with tuning the engine. 

I found that after altering the Air Filter system the engine was bogging down - this is a good thing!  It indicates that the engine is now getting more air. The trike started, and ran smoothly up to about 20mph, and them lost power - lack of fuel in the mix.  This means that the main jet is too small!  The first 1/4 of the throttle is controlled mainly by the needle jet, and the main jet takes over after this.  This would be why the engine is OK up to about 20mph, and has problems after that with the new air filter system.

I can now go ahead and start carb tuning.  The main jet is a 107 and I'm going to start out with a 120 to see if I can improve the performance.  It will probably involve several attempts to get the correct main jet for best performance without foulin gor burning the plug,  and then I may also have to play with the other jets, needle etc, to get smooth operation across the full engine rev range.  Watch this space.