Unfortunately the big egos go to all sorts of efforts to make sure their videos come up top when you do a You tube or google search.
As THEY are what is important , not your problem the videos are really about them showing you how smart they think they are.
With a hand held that does not rev as high as you think it should , the usual culprit is the exhaust screen or exhaust being blocked and choking the engine.
A blocked inlet screen causes the engine to run lean which on two strokes makes them run too fast and lack power.
If the screen on the carb was partially blocked then the filter in the tank requires replacement or the carb screen will block again.
Cube carbs are a pressure vessel and run at around 7 psi so a really filthy looking carb screen will still pass sufficient fuel to reach full revs.
Nearly every donkey brain on You Tube will show you them blasting carb cleaner through every hole to "clean them out" with gay abandon.
Very few tell you which ones to spray and which ones not to.
Depending upon the exact carb there is from 1 to 3 check valves.
Carb cleaner will destroy many of them and cause them to become stuck in the closed position.
That is why Walbro went to the expense of making the very expensive carb cleaner that is check valve safe.
When blowing out a carb, you should , where ever possible blow the passages out backwards WITH LOW PRESSURE AIR , not a dust gun hooked up to your sand blasting compressor running 150, PSI that will force the crud so tight that you will never be able to shift it.
Like you, when I started out I watched all of the clots on U-toob and did what they did as cube carbs were totally new to me.
However since then I have learned better and never pull one apart unless the diagnosis is pointing to an internal carb problem .
And over time I have come across some of the better informed presenters and of course gotton my hands on some of the better service manuals.
In your post you mention a lump of the gasket stuck on.
This always happens and when it does you fit a new one that is nice & soft so can conform to the surface and make a proper seal.
If you run a cube carb on a wet stone you will see that the machined surfaces are not smooth but contain machining grooves.
This is intentional and is there to allow the gasket to fill in the grooves and thus make a pressure tight seal.
It also provide an escape path for air that gets trapped by the gasket.
It is also why the gaskets stick and break up when you are trying to take the carb apart and also the reason why you should never reuse them.
So now days the only time I jump right in & pull a carb apart is when a customer comes in with a tool that worked fine last season, has not been used for months and now won't start.
On those you can be fairly sure the carb will be gummed up, but only around 1/3 will be able to be cleaned properly.
Around here I have become the "go to guy" for problem hand held tools and this is purely because I replace fuel lines, filters & grommets
So when I have adjusted a tool & sent it back, it works as it should for several years till it is time to replace the fuel lines again.
Now back to you and your problem
Pull the carb off the engine and leave the fuel lines attached.
Double check you have them on the right way round.
When you pump the primer bulb the line that blows out the fuel gets connected to the short fuel line that stops just inside the tank
Turn the carb sideways and blow air through the venturii and watch for atomised fuel mist coming out the engine side of the carb.
It should be a strong dense stream.
If not then you have probably wrecked the check valve, in which case it will be a lot easier & faster to replace the carb.
And Zama carbs have the work Zama casr into the body or pump cover depending upon where the pure bulb is located.
If it does not say Zama then it is not a Zama
