This is taken from sohc4 site. It was a big help when tuning my carbs. Thought it might be of some help.
How is carburetion affected by throttle opening, temperature, humidity etc?
Throttle Position:
Idle Set at 1700 RPM + or - 100 RPM
Idle -> 1/4 Air screw Turn in for Richer out for Leaner
1/4 -> 3/4 Needle Jet Clip up =Leaner Needle Clip Down = Richer
3/4 -> Full Main Jet (bigger the number richer the mixture)
Conditions:
Air Temperature High = (less air so you have lean out the mixture)
Air Temperature Low = (more air so you have to richen the mixture)
Altitude High = (lean the mixture)
Altitude Low = (Richen the mixture)
Humidity High = (Lean out the mixture)
Humidity Low = (Richen the mixture)
How can I temporarily richen or lean my mix without fiddling the carbs
Colder Glow plug to Lean it
Hotter Glow plug to Richen it
I need to sync my carbs but have no vaccum meter. How do I bench-sync?
When I rebuild a set of carbs, I always bench sync them before I re-intall them. Basically, I use a 1/8" drill bit as a gage. Here's how you do it: Adjust the idle screw (the main one) until the 1 carb outside of it is open enough to just let the 1/8" drill bit through. Then adjust the _sync_ screws on the other 3 carbs until the drill bit just fits them as well. You'll probably want to close the idle screw before you bolt them back on the bike, 1/8" openeing is pretty big. This isn't a perfect sync, as there are other things that will affect the airflow to a given cylinder, but it will get you pretty close.
Comment from Bob Wessner:
I was reading the FAQ's, on carbs to be specific, about bench syncing. It's probably trivial and only affects those with pre-K1 750's, but they really can't be bench sync'd off the bike because of the four independent cable linkage. I must have read through I don't know how many earlier posts on this trying to figure out how it would possibly help on mine until it dawned on me that as described, it only works for models that have the carbs all linked via the bar, so to speak. Jus thought may a note to the affect that the described procedure is for K1's and later might be useful.
How do I tune the carbs?
1. Pick the main jet first. You can take a plug reading at wide open throttle. Accelerate over a long distance (preferably uphill) getting into 5th gear and keeping throttle fully open. When fully tapped out, grab the clutch and hit the kill switch. The motor should stop immediately, then look at the plug. Should be tan, but not too dark.
2. The pilot jet affects cranking, idle, and particularly acceleration from idle. If too lean, the motor will hesitate when accelerating (in neutral) off idle. If too rich, motor will smoke excessively, foul plugs, and be unresponsive off idle. Driving along in first gear just barely above idle, there should (actually MUST) be some blubbering, but it should clear up immediately at about 1/16 throttle. Air screw affects pilot jet somewhat. It is useful in 1 to 2 1/2 turns out and within the extremes of this range, is about like changing pilot jet 1/2 step (if that were possible).
3. Slide cutaway has a tremendous effect on throttle response. Its range of operation is approx 1/16 to 1/4 throttle. Too lean and the bike will be a bear to control. Too rich and throttle response will be sluggish. Slide cutaway and needle DIAMETER are very similar in their actual effect on jetting. It's usually easier to leave the slide stock and try to get jetting optimum with the needle diameter.
4. The needle is perhaps the hardest part of jetting. There are various aspects to selecting needles. Hopefully, the manufacturer was pretty close so all you have to do is change the clip position. This, however, only affects the range around 1/2 to 3/4 throttle. By selecting special needles, it is possible to tune any desired throttle position, but hopefully you won't have to do that. It's not as easy as picking the right clip position. If the clip is too lean, the bike will be VERY crisp but after warming up it will usually develop a hesitation when accelerating using mid throttle positions. If too rich, the bike will be slow and unresponsive and you may even get the blubbers
typical of extremely rich jetting.
5. Note we have been talking about throttle POSITIONS. It is useful to mark your throttle grip so you can SEE what position your hand is in when jetting. Remember, it's the throttle POSITION, not the engine rpm that you're using to jet the motor.
6. In general, lean conditions will overheat a motor. It might take a few seconds (main jet or needle clip too lean) or 30 minutes of woods riding (needle diameter too lean), but an overheated motor will become harder to ride, lose power, and hesitate on acceleration. If you're lucky and smart, you'll recognize this before you seize it. A motor jetted too rich (in any one area) will suffer loss of acceleration and responsiveness, may smoke, and may foul plugs. It is possible to have one jet too rich and one too lean. The bike could display both lean and rich characteristics depending upon where you hold the throttle.
7. To develop your skill at jetting, you need to experience too rich and too lean with EVERY jet (pilot, needle diameter, needle clip, and main jet). Only after you FEEL what too rich and too lean is will you be able to jet your bike perfectly. Start with the main and go way too rich and feel it blubber at full throttle, high rpm with low load. As you come down, you'll feel the power and responsiveness build considerably and the bike will begin to rev out cleanly.. About the time that the plug starts saying "too lean" you should begin to notice hesitation on full throttle acceleration and a reluctance to rev very high. Don't press your luck. One main jet size or one needle clip position is often the difference between a bike that's unpredictable and miserable to ride and one that always has great power whenever you twist the grip.
What happens when I turn the airscrew out - richer or leaner?
If your airscrew is on airbox side of carb, turning out will lean mixture; opposite if airscrew is on engine side of carb.
