Motorcycle Repair: idle problem, screw nut, adjustment screw

Question
i just bought a '77 cb550 four.
the problem i am having is that to start the bike i pull the choke out and it revs high (up to 6000rpm) so i work on pushing the choke back in and calm the bike down. but i am never able to get the choke all the way in and the bike idling at a normal level. So then I have been riding it with the choke pulled out and when the bike seems to warm up the idle will start to go down towards a normal level but the bike always stalls. So i have to always be giving it a little gas to keep it above 2000rpm's otherwise it stalls.
thanks
timmy

Answer
Timmy, you could have multiple problems there....

First do a full tune up on the motor... adjust valves to .002 and .003 In/Ex, check compression.

Remove the point plate and check the mechanical spark advance for correct operation.. should spring back after being turned in the direction of advance. Lube the point cam and reinstall everything.

Clean the point faces thoroughly, set gaps so they are .012"-.014" at the widest point, then adjust point plates so the points just open at the F mark on the 1-4 and 2-3 marking alignments.

Drain the carbs at the float bowl screws and capture what comes out. I suspect that your idle jets are plugged up on one or two carbs, which causes stalling, forcing you to keep the revs up off the idle circuits to keep it running.
If a lot of water, debris or old gas deposits come out of the bowls, you have a couple of choices.
#1 overhaul the carb rack
#2 use Yamaha Carb clean solution as directed.

When you are working on carbs, check the choke cable down on the rack and watch where the "fast idle" section begins to raise the carbs during CHOKE operation. There should be a cam and an adjustment screw/nut that you can carefully set, once everything else has been done.

Note: when you drain the carbs and then try to refill them, often the floats hang down and the needles will cock in the valves, causing the carbs to flood. When that happens, just turn off the fuel, rock the bike back and forth and/or tap on the carb bodies with a plastic mallet a little. This will generally reset the floats and valves and it will stop leaking from the float bowl overflow tubes.

Bill Silver