Hi everyone,
I'm new to the forum and new to nitro engines as well.
I just got my first nitro car- the thunder tiger mta4 s50
After going through youtube vids i believe my truck is tuned ok.
The issue worrying me is there is alot of unburnt fuel being discharged at the exhaust.
Can someone please tell me what is the right amount of fuel discharged if any?

There will always be fuel coming out. Especially the s50 as it has a big engine and the exhaust is not a Performance tuned resonator. So there will be more fuel coming out than other cars. and  do check tune if there is too much fuel coming out

Thanks pravesh.
I believe the low speed needle is tuned right as it passes the pinch test. The engine quits after about 5 seconds after pinching the fuel line.
is that right?

Pretty much.  Around 4 seconds on the pinch test is good. 

Also, if this is the first couple of tanks, then keep running the engine a bit rich. You can lean it out further beyond that.