I like your basic engine setup with after market head & Dellorto style carb. I've used these two item's on all my 2 strokes since 2012 & know they work. The "Miami" style expansion chamber + a higher compression ratio head probably does lean you out and normally an "up" jet for the carb is needed & should really improve performance. Check your plug to see if you're currently running lean, my guess is you are. Pushing more air through the carb will demand more fuel as well (depends on the 21 mm carb jetting) if you do change to a different carb. Keep in mind my altitude is about 1500 ft. above sea level so if you are near the coast you have higher air pressure so more fuel, larger jet, is often required; even on a stock kit motor. Higher elevations just the opposite. Read the plug and adjust accordingly.
My 5+ hp engines pull an extra half a horse on the dyno by just removing the air cleaner, same style air filter you're running, but when we read the plug it showed lean, with a up jet it gained a bit more, 2/10ths. hp. with air cleaner off and the plug read perfect, but put the air cleaner back on and the dyno showed about a 1 hp loss, just over 4 hp and the plug reading was really wet. Any effective engine mod will alter the fuel flow requirements. Major changes require a lot of patience to get right. When I changed from piston port to reed valve engine setup the addition of a third transfer port and a piston window; getting the right plug and carb jet setup was not easy and this was made more difficult by my addition of a different style expansion exhaust halfway through the process. I stuck with the Dellorto carb & it now runs great. Would it run better with a larger Mikuni carb properly jetted and set up? Possibly, but I like the street manners of this setup so I'll probably not experiment...right now.
I often run a 48 tooth for town riding & yeah the pull is really amazing though it limits cruising speed a bit compared to a 44 tooth.
Have fun with it & my guess is it runs quite well as it is.
Rick C.
