Suzuki GP125 running problems

[Student]

Keep having to do repairs on this bike but I wont let it go
It's an 1984 Suzuki GP125 2 stroke.
Main problem at the moment is that it wont use all the revs, it wont go over 5,500 sometimes 6,000 and I basically have a top speed of 30 mph which I can do on a push bike :c
My friend has said it could be a the gasket in the float chamber is rotten and is letting air in so the float doesn't stay at the right level thus stopping any power coming through.
He's gonna try get some gasket paper from work and fix that but he's not a motorbike mechanic so I was wondering if there could be anything else that might be causing this problem?
Appreciate any advice (except to scrap it, I'm stubben and want it to work)
But thanks for your time
Pugs

[ms51ves3]

Spark plug.

Sucking air in from around the inlet rubber so running super lean and getting minimal fuel. Check for splits.

What did it used to run like?

[Student]

Spark plug's been changed since
And I don't know what the inlet rubber is or where to find it

When the thing would work it would go up to around 9k revs, could probably go up to the 12 but 9k is the start for the red line so never bothered taking it past that.
But after around 20mi the spark plug would stop working and come out black

[ms51ves3]

The inlet rubber is the rubber part in between the carb and engine.

Could be running rich or over oiling.

[Student]

We where told the grey cloud of smoke coming out of it was to do with the float by the guy from the suzuki garage, hence why we know the gasket is knackered.
And when my friends back I'll suggest the rubber inlet to him he'll have a better idea of how to get to it.
I'll let you know how it goes when we've fitted the new gaskets in.

[ms51ves3]

[Wozza]

If the float bowl gasket was gone, air wouldn't be drawn in - fuel would be pissing out!

Get a Haynes manual, clean the carb, check/adjust float level, check inlet rubber for splits (if it's not between carb & engine, it'll be between airbox & carb), check fuel tap filter and sediment bowl and clean where necessary, rinse out tank (with petrol) if there's crap in it, check cap for airflow, check fuel pump adjustment, decoke exhaust. After that if you've still got problems, you might want to check inside the engine to see if you need new rings, a new piston or even a rebore.

[Student]

I was told it was either the float or my oil pump adjustment that caused the grey smoke. all that happened when I looked at them is that I got to my current situation
The other thing I've looked at is air filter which was just completely replaced as it crumbled out of the vent
And the Carb is pissing fuel out :p Apparently as the fuel goes out it sucks air in, I don't quiet understand the logic but I still think the gasket needs to be replaced :p

P.S. And I have the Haynes manual for it. It just doesn't cover this problem, or if it does it's not easy to find

[ms51ves3]

[Student]

Bike now makes lots and lots of noise
And gets from Point A to Point B making more noise
and goes bloody fast

So yeah my guess it works, just need to get it MOT'd and insured before so I can tax it (Well it's got no MOT everything else last til the end of the month)
So gonna look at my bank on the way to work and see what I can do for it's MOT

Thanks for all the help guys (And encase your wondering, it was the gasket in the carb above the float chamber, going to look at those other things if it packs in again any time soon)
____________________
Current bike/project - Suzuki GP 125
Wish bike - Suzuki Gladius