All of Danny's "tests" and conclusions have me a bit confused so I will put down some GENERAL steps for troubleshooting this issue. If any of these have been covered, I would still retry them in the order given so that these can be totally ruled out. I suggest testing to see if a plug is firing by taking a spray bottle of water and spraying the pipes after they have had a chance to warm a bit. After about 30 seconds, a hot pipe will vaporize water while it will run down off one that is mearly getting hot from proximity to the hot pipes but the cylinder isn't firing:
1. Compression check with gauge on all cylinders - Low compress WILL cause a cylinder to not fire. The MOST repeat MOST common reason for lack of compression is that a valve (or valves) have NO clearance and are partially open - this leads to FOULED plugs which will also cause the cylinder to non-fire
if compression checks OK then step 2
2. Electrical issue. If ONE cylinder is not firing, this imples the coil is OK but either the plug, plug wire, connection to the coil or the plug cap are at fault. FIRST - The coils fire in pairs. If #3 isn't firing, swap the #2 and #3 plug wires. If the problem remains on #3, then REPLACE or SWAP the spark plug. A bad plug DOES happen. If the problem moves, then check the seat of the plug wire in the coil. Remove the wire, cut off perhaps a 1/4" and reseat it. If that doesn't fix the problem, replace the wire and cap.
If this doesn't fix the problem, go to next step:
Step 3 is carburetors. Put in a clean set of spark plugs as the plug for the non-firing cylinder is likely fouled from the non-combustion. Start the engine and then rev it to perhaps 4K rpm. If the bike doesn't idle but "cuts in" when rpms rise, the pilot circuit has blockage in either an air path or fuel path. Clean the internal passageways completely and retry to see if the cylinder has combustion (water test on pipe) at idle. If it doesn't you might need professional carb help since whatever was doesn't didn't work. If the bike doesn't "cut in" when you rev the engine, reset the float level using the Service Fuel Level method (set the float level WET). There is little liklihood that the #3 cylinder fuel pipe is obstructed if #4 is getting gas. If the problem occurs on an OUTSIDE cylinder, there is the possiblity that the fuel pipe itself is plugged or obstructed. Another thing to check is that vent ports are free and unobstructed and that the carbs are drawing gas easily as there is no vacuum lock. In other words, if the vents are open, gas can be locked in the tank if the tank vents are plugged. Try opening the tank gas cap when the bike is running on 3 cylinders to see if the cylinder kicks in and starts running. It could be that one carb's float level is a shade low and the bike is having problems drawing in gas. The last thing that is unlikly but possible is that the carbs are so far out of sync that one carb is getting almost NO engine vacuum at idle but even then, all four cylinders should kick in once the slides are raised when revving the engine.
