What type of fuel are you running it on, you want to be using 15% - 20% and a quality brand such as Blue Thunder.
Also replace the glow plug with new just to eliminate it and fit a new copper sealing washer at the same time, again use a good brand such as O S.
Give the engine a once over and make sure that all the screws are tight and that everything is sealed properly and clean the air filter.
Set both the low end adjustment and top end adjustment rich, then with the car on a stand you want the car to idle for 9 seconds and be clean to rev up, at 10 seconds it should bog a little. Thats a general rule for the bottom end.
The top end really needs to be set whilst using the car so as to avoid over revving it, drive the car about and you should always have smoke coming from the exhaust even when running flat out and then just lean the mixture gradually. Keep checking the engine temperature by spitting on the cylinder head and it should slowly evaporate, if it jumps off and bubbles away instantly the you need to richen the top end back up.

One other thing, how much fuel has the engine had run through it as they don't last forever and you could be looking at a re-build, also make sure that your fuel and pressure pipes are ok and have'nt got any small holes in them.

Sorry about the essay mate but check these things first, hope it helps