Disagree with idea of tuning low-end first - subsequent adjustment of main needle can throw off the low-end. Here's my tuning method:

Step 1 : Warm up the engine (at factory settings if the tune is way off), run 1/2 tank. Refill.
Step 2 : Adjust main needle for power, good smoke at full throttle. Temp less than 250.
Step 3 : At idle, pinch fuel line at carb inlet. RPM should rise slowly, engine quits in 5 secs.
RPM's rise quickly - Low-end is too lean.
RPM's don't change for a while, then rise - Low-end is too rich.
Step 4 : Run engine at normal race pace, then let idle for a minute or so. Measure Temp.
Temp at idle rises - Low-end is too lean.
Temp at idle falls - Low-end is too rich.
Step 5 : Fine-tune main needle to keep engine temp under 250 at race pace.

Keep in mind that mixture will lean out as fuel tank empties - always tune on the rich side with the tank at least half full.