>>>Typical lean conditions:

* Poor acceleration - feels flat
Engine doesn't respond when throttle is snapped open - picks up speed as throttle is closed
Engine runs hot, knocks, pings and overheats (end result- hole in piston)
Engine surges or "hunts" when cruising at part throttle
Popping/ spitting through carb when throttle is opened, or popping and spitting through pipe on acceleration with a closed throttle (classic lean pilot circuit symptoms)
Engine runs better in warm weather, worse in cool
Performance gets worse when the air filter is removed


>>>Typical Rich Conditions

* Acceleration is flat, uneven
Engine will "8 stroke" as it loads up and skips combustion cycles
Throttle needs to be opened continuously to maintain acceleration
Engine works better when cold
Black smoke from the tail pipe
Poor fuel economy
Engine performance improves when air cleaner is removed
If the pilot screw is overly rich, idle is rough and the engine won't return to idle without blipping the throttle
Black sooty plugs, sooty exhaust pipe

How do I diagnose faults "on the fly"
When you are limited to street riding, take note on how easily and quickly the engine reaches the proper RPM for shifting gears. The engine should accelerate smoothly and quickly through all gears. When the main jetting is to rich, the engine will feel sluggish and acceleration will 'feel' slow. You can check the main jet by quickly closing the throttle from wide open to 7/8 position when the engine's RPM is greater than 4500. If the engine accelerates slightly, the main jet is to lean. A larger main jet is needed. If the engine hesitates or misses slightly, the main jet is to rich. A smaller main jet is needed. If the engine just slows a slight amount, the jetting is very close to correct.
Another test is to accelerate through the gears at full throttle. If the engine backfires through the carburetor, misses, cuts out or quits running, the main jet is lean. Increase the size of the main jet. If the engine acceleration seems sluggish, does not react to the throttle or sounds flat, the main jet is rich. Decrease the size of the main jet. The main jetting can be set quickly at a 1/4 mile drag strip. For this test, you can ignore the ET (elapsed time). Making sure the engine is warmed up, make your run down the strip making note of your final MPH. Keep increasing the size of the main jet until MPH begins to drop. Then drop back one jet size. Your jetting should now be correct.

To determine if the bike is lean (to little fuel for the amount of air reaching the engine through the carburetor) at any given throttle opening, partially cover the air-filter intake with a piece of duct tape; if the carburetion improves, it's running lean. If you suspect the bike is running rich (too much fuel in the air-fuel mixture)), remove the airbox top or the air cleaner element; if the changes are for the better, the bike was running too rich. If your bike is equipped with a manual fuel shut-off (or you're clever enough to disconnect and plug the fuel lines), take the bike for a ride with the fuel turned off. If it runs worse as the float bowl drains, it's lean. If it gets better, it's rich. If you rev the bike and the revs hang up after closing the throttle this = Lean; if the revs dip down then come back up = rich.


How do I adjust the carb?
The backfiring indicates air/fuel mixture or pilot jet leaness. I'd start, as you correctly stated with the idling mixture as it's the easiest and cheapest. Remember there's another carb under your tank which you'll also have to do. Manufacturers specs are normally one and a half turns out from the slightly seated position - don't force the screw it's got a taper on the screw you're turning as well as in the carb. Start the engine and get it to working temp. Light a cigarette or whatever you smoke as you'll be busy from here on. You'll be letting the engine run for a while so do it outside where there's air circulation or put a fan on the engine and put the beers within reach. Adjust the idling speed to the spec or to where you can hear it's running at a constant speed (the idling speed is adjusted by hand by turning the brass screw with the spring on it sticking out of the back of the rear carb). Now turn the pilot screw out one quarter from the manufacturers spec. If the engine speed drops, return the screw to where it was and turn it in one quarter. If the engine speed drops, you're OK (and I'm OK). Drink the beer.
Don't go for a test ride after the beer. If the engine speed increases as you turn the screw out, keep going until you reach the point of max RPM. If it takes more than 3 turns for the engine speed to level off, the pilot jet is too large. Install a leaner one. This will probably not be your scenario. If the engine speed increases as you turn the screw in, keep going until it levels off. If the pilot screw ends up less than half a turn open, the pilot jet is too small.Trick : When you've found the peak idle speed, turn the mixture screw in one quarter turn. If it doesn't change the idle speed leave it there. If it does drop, return it to the last setting.