The best dyno graph.  Really the only way to determine the best tune..  Without a dyno most just tune so it doesn't have any major problems(backfiring, detonation, fuel fowling, etc).  But trial and error with horsepower and torque graphs.  And then it also depends on your goals.  Best power for performance driving can be different from cruising can be different from getting most peak horsepower just for the sake of the number.

well tuned can mean a lot. You can tune for low end, peak HP, high MPG, etc.    
  I assume you mean how can you be sure your carb is tuned properly.    
  Only way to really do that is check your plug at idle, midrange, and WOT. If you're stock and properly tuned you're lucky. Idle for a few minutes, then check your plug (and all that that process entails). If its white you're lean, adjust idle mix screw and/or go up one jet size. If its black you're rich, adjust idle mix screw and/or go down one jet size. Idle a few more minutes, check the plug again. Etc until the plug is a light brown.
   For mid range (after you've got the pilot circuit right) run around a few miles. A short distance from home (or where ever if you want to bring tools) get in 2nd or 3rd and twist the throttle to 1/2 and run at a steady 1/2 throttle for 5-10 seconds. Simultaneously pull the clutch lever and hit the kill switch, then coast to home or where ever and check your plug. Again, white = lean, black = rich. If you're lean shave down the white needle spacer or replace with 4 or less #4 washers. Check your plug each time you make a change and adjust accordingly. If you're rich (on a stock machine) you'd be the first. IF that is the case, add a #4 washer and check your plug. Keep adding or removing space and checking your plug until the plug is light brown.
  Main circuit...get in 3rd-5th and run at WOT (after you've got the pilot and needle spacer/midrange right) for 5-10 seconds and simultaneously pull the clutch lever and hit the kill switch. Check plug. Lean, go down one size on the main jet. Rich, go up one size on the main jet.
  Once you think you've got it right...start at the bottom and do it all over again. After the second run through you'll be dam near perfectly tuned.
  Yes...its a super tedious PITA.

For more info on the air mix screw, white needle spacer, and jets...just search. Links and answers are everywhere. For a stock or near stock bike buy a jet set from Lancer. Has everything you need to do the above and get it right.

It's a big guessing game w/o a dyno, air/fuel meter, and a lot of time.

To me, "properly tuned" means it pulls as hard as I can get it to at the top end and a smooth pull from idle on up. That means no flat spots, bucking, popping or other rude behaviors It sounds so simple but it is a pain.

As a side note: I've had a lot of success tuning from the top down. That means getting the main jet right first, then the needle(s), then the float(s), then the pilot system. Every circuit  will affect the one below it so it just doesn't seem right to start w/ the pilot when the float level will affect that, and the the needle will affect it some more, ect. Of course, this only works if it close enough to run at the low end to start w/. That can be a whole nother headache if you have a seriously modded bike.

Here's some of the best tuning advice I've been able to find:
http://www.factorypro.com/tech_tuning_procedures/tuning_carbtune,CV,lower_rpm...

onelunger wrote on 06/14/10 at 04:33:49:


that article is good but i don't get the section on main jet selection  it sais to select the main jet that performs best at high rpms, by seeing how the engine behaves when its cold or hot. i dont know about you but WOT when the engines cold is always a bad idea isent it?

How to test your main jet....

"To test the main, accelerate from 30 or 40 mph, in 4th or 5th gear at full throttle for several seconds, then reduce throttle by about 1/8,...if power increases for a second, you are lean on the main jet.  Go up one jet size and test again"

Its easy to know when  its "Right". Ya get more tickets in less time.

jabman wrote on 06/15/10 at 03:50:21:


The other side of the coin for a quick and dirty test of the main jet it to try step by step larger main jets until you get to the one that causes the engine to stumble at wide open throttle; at that point you are too rich, so back down one size and you are good to go for the main jet.