So I recently purchased this buggy and to get it to run for the break in procedure I had to have the HSN and lsn right much richer than break in settings (both flush) with the carb opening set way less than 1mm, almost closed.

So I assumed I had an air leak but continued with break in since I had some raw fuel spitting out of the exhaust, before tearing it down to sealed it up.

I also checked the needle o-rings and they look to be fine.

Now here's the current issue...

When tuning for performance the only balance I can seem to get between off the line and top speed is with the lsn 1 -1.5 turns richer than flush and HSN about 2 turns lean from flush. Which to me whatever runs best doesn't bother me where it's set, just giving as much info as possible.

So I can tell the engine isn't reaching top speed/rpms, it just kind of lays flat at the very top end. 1/8 - 1/4 turn lean on HSN from here I get lean cut-out, 1/8 - 1/4 turn rich and I get even more reduction in speed/rpm. Idle lays down good, smooth, and stable so i havent been messing with the lsn.

Tryed the stock hpi R5, o.s. #8 & #9, and McCoy Mc9 glow plugs without affect. Which I do know they're similar ranges.

Nothing in drive train is in a bind, it'll roll forever.
Also no fuel/oil coming out from the front bearing.

Sorry for the long post, didn't want to say hey I can't get my car tuned.

What can i do next??

Your plugs might be way too cold unless you're running in really hot weather. Try a P3 plug from O.S or Protek. I'm assuming that engine takes a turbo plug. If not turbo, then whatever the hotter version plug is that fits that engine.

Went back to tuning with the os #8 instead of the stock hpi cold plug, got SLIGHTLY better performance but still can hear it being limited in upper rpm.
I hope it's just not just the way this engine is. I know it's not a race mill, but the 2.5 in my rustler screams compared to this thing, by sound.

Seems to have adequate pinch & running vp 20% master basher

Edit: going to try a traxxas long reach plug to up the compression just to see, calculations shows enough clearance not to worry