What I'm trying to say is that there's no knowing whether four sizes is enough until you test everything out.
A "plug chop" is the testing process. Basically it involves running the bike at given throttle position for about a minute and then immediately killing the engine with the clutch pulled in. You pull out the spark plugs and take a look at them. The ceramic portion below the electrode should be a light tan color if everything is perfect. Dark brown or black means you're running too rich. White means you're running lean. White with metallic flecks means you're WAY too lean and about to toast your engine. It's best to do this process with new, clean plugs, each time. If you don't have too many plugs laying around or can't afford a dozen new ones, try to clean them as best you can with a wire brush between uses.
To begin with, it helps to have a rough idea as to whether you're running rich or lean. Lean symptoms include the following:
- Poor acceleration
- Slow response when you snap open the throttle (less applicable to CV carbs) but engine may pickup for a second or two when the throttle is snapped closed (oversized main jet could mimic this as well)
- Engine is hot and pings or knocks
- Uneven running when cruising
- Performance suffers when the air filter is removed
- Popping sound from the exhaust when decelerating or popping sound from the carbs when accelerating
- Better running in warm weather and/or high altitudes
Rich conditions will look/feel like this:
- Engine won’t return to idle without blipping the throttle
- Idle is rough or lumpy
- Poor fuel economy
- Smoky exhaust
- Poor acceleration
- Performance improves when the air filter is removed
- Better running when cold or at low altitudes
You repeat the plug chop at least three times to get a basic tune. First you get things dialed in at idle. This means ensuring that the carbs are synced and then getting the bike up to temp. Turn the dial of each air mixture screw until you get the maximum RPM out of the engine and then adjust the idle screw to get you at 1200 RPM or so. You should be running a good A/F ratio at idle now.
Assuming your bike feel pretty close to target or perhaps running a little rich, it's time to move on to a plug chop at Wide Open Throttle. This step is not advised if you're running very lean, so take a look at the lean symptoms above and decide if you need to go up a jet size or two before you try this next part. Anyway... find yourself a nice long straight section of road without too many police around. A straight uphill run will work quite well for this, too, without getting so much speed. Get going in top gear and open the throttle all the way up. Run at WOT for a minute and then hit the kill switch, pull in the clutch, and come to a stop. Pull out the plugs and read them. This will tell you if you're running rich or lean on the main jet. Switch out main jets until you get a good reading from a WOT plug chop.
With your main jet sized correctly, you can now do a 3/4 throttle run and check the plugs. This will tell you how closely your needle jet is sized.
After getting the needle jet dialed in, do another run a 1/2 throttle. This will tell you the necessary adjustment on your jet needle. If you're running lean, you want to raise the needle. If you're rich, lower it. Most needles will have five notches in the top than you can use to raise or lower it. You can also use small washers to get more height if necessary. A new needle is not usually needed, but can be required if you can't get a good tune out of the one you have. Needles also have varying degrees of taper. The sharper the taper, the fast the fuel starts flowing.
Finally, do a 1/4 throttle run and this should tell you the state of your slide cutaway. Lean means you need a small cutaway section whereas rich means you need more.
What size do you think for this job? I'm thinking 145... that's 4 sizes up... Please let me know your thoughts if you are so versed. Many thanks! Cheers 
