have a 1980 Suzuki TS 125 with a Mikuni VM type 'round' carburetor.
It did not start this spring, so l took the carb out and apart, and
cleaned it complete (never been done).

The bike now starts (after lots of trying, ultimately tow starting it
by pulling it with a car).

But in only takes 1/4 throttle, than chokes and would die if not
closing the throttle immidiately.

l had tightened all interal screws, and no start to think that there
may be a mix screw inside that adjust the air/fuel mix.

a) can someone please let me know if that is the case?
b) what screw it is?
c) how to set it to get the bike going again

well it could be a main pin and gas pin mix up coz they both look almost similar,take the carb apart again and check that all is in place..since its a two-stroke bike l advice ya to check on the spark-plug and the fuel pipe lines.

sounds more like there is still trash in one of the jets or passages. did u remove all jets & thoroughly clean those too? needle jet, pilot jet & main jet.

these had very simple carbs on them & not much other than clogged passages to mess with. l do not even recall there being an air screw, could merely raise or lower needle for adjusting.

http://powersportspro.com/pages/parts/viewbybrand/1/Suzuki.aspx

did u also drain the gas tank, flush the tank, remove & flush the petcock screen?

also clean the air filter, put in a fresh spark plug along with fresh gas / oil (unless the oil pump is still intact).

very simple design.

A clogged pilot jet in the carb is the most common problem.
The opening for the pilot jet is as small as a pin and is easily clogged with bad gas.
Remove the pilot jet and hold it up to the light - you should be able to see through it.
Clean it until you can.
Inside of the float bowl, the main jet is in the center, the pilot jet is to the side of it.