WHY DOES MY BIKE NOT REV THROUGH 6000RPM

pull your muffler off and see if it revs up, if it does then your spark aresster screen or muffler is plugged, from carbon or mud dobber hornets

Try a new spark plug and fresh fuel, clean/replace the air filter.

There are a few things to check, if the muffler has a spark arrester gauze in the out let this may well be blocked, remove the muffler and the gauze, does the engine now rev? if yes either the park arrester is blocked or the muffler itself is blocked, if this does not cure it, check the flow of fuel from the tank to the new carb, replace the filter in the fuel tank and try again, if this does not help try running the saw with the air filter removed, if it revs normally the filter is blocked.

If is runs better with full choke, then the bike is lean, check for air leaks at the carb manifold, vacumn cracked hoses, non standard exhausts, perhaps the mufflers have rusted out while sitting

Try changing the spark plug first and clean the air filter.

clean the carb,check spark plug and air filter

Check the air cleaner and muffler for plugging. Try turning the idle speed screw (not the L jet screw) CW one full turn. Does it now idle? If the chain keeps turning at idle, back off the speed screw until the chain stops after revving the engine. When the engine won't start, remove the spark plug and check for blue, snappy spark. If the plug insulator is black, try a new correct type plug. If sparks ok, then squirt some fuel mix into the plug hole, replace the plug and try to start. If you get a pop or two, then fuel delivery is a likely problem. If it again runs, the plug may have been the problem. Otherwise, check the fuel filter, fuel line, and carburetor for any loose fasteners. Finally, run the engine at full throttle--it should 4-stroke with no load, but immediately 2-stroke when cutting. Adjust the H jet needle to achieve this. hope this helps!

Target your inspection towards the 'spark arrestor screen' in the outlet of the muffler.

Overfuel or 'rich' condition
Basics to check:
1) Spark plug - brown or dark brown - OK
a) is it carbon or fuel fouled
b) is there spark

2) Muffler remove for inspection
a) exhaust screen clean or plugged
b) inspect cylinder wall/piston as the flywheel is slowly rotated
3) Check Air filter for fuel saturation
4) Allow engine to run for 5 minutes to excess fuel from muffler
5) Fuel mixture ratio: Make sure the oil mix is per your manufactures recommendations
6) If after the above the engine is still smoking and blubbering:
Adjust carb mixture screws to a 'less rich' setting
*NOTE: only move mixture screws 1/8 of a turn at a time,
and try operation before any more adjustment

I’m happy to assist further over the phone at https://www.6ya.com/expert/rolandw_c013176d62ee17ae

It might be a spark plug issue, when my DT175 fouls out a plug, it is gutless and only runs to about 5,500 or 6,000 RPM in gear or neutral or whatever, try changing out the spark plug, if you haven't already.

No, the rev limiter resets to 6000 rpms when the battery goes dead or is changed. You have to reprogram the rev limiter to allow it to rev to 11,500 or more, but i am sorry to say that i can't recall the sequencevof buttons to reset it, which shold be in your owners manual. This is not an upshift light!