My 1980 GS550 Suzuki idles to high, about 3 to 5000 rpms. how do i adjust the idle.

It's a guess, but looking at the wiring diagram, very loose contacts inside the starter relay.

https://www.justanswer.com/motorcycle/1dzu4-anywhere-online-diagram-1983-suzuki.html

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it sounds like to me you need another carb gasket. It is leaking vacume past the gasket and causing the bike to pull more fuel to accomadate the air so it is running to fast. If that doesnt fix it check out throttle cable to make sure it is adjusted right

could also need a idle jet, idle screw, could be muck in the float bowl.

Don't ask such questions here is advisable to you, as setting your vehicle on anybody else's remote instructions maybe of harm to you and your vehicle, I'll suggest you to contact a Professional Mechanic to do so, he'll need your own experience at both RPMs and then will set one to your choice, according to your Test Drive at both.

some bikes have idling screw on carb.have you check to see if your carb booths are seated and not sucking air.

the idle adjustment screw is located between the number 2 and 3 carburator float bowls bottom rear. I can bairly get my hand on it, but found that a flat blade screwdriver works fine for making ajustments. backing out the screw lowers the idle speed, while running it in increases it. To adjust make sure the motor is warmed up and the choke is off. Make adjustments from the right side (looking at bike from the back), by pushing with the screwdriver on the knurals of the adjustment knob, pushing knurals up backs the screw out, conversly down runs it in. Try for around 1000 rpms for your set speed. You want it to idle smooth and low, but you want it set so it won't die out when you come to a stop when you are riding. If you can not get the idle in this range, then there is some other problem needing attention. However, the idle at times may run a little bit higher than normal when you come to a stop after a hard ride, and should return to normal set speed after it cools down some. You should also make sure that the throttle cable is set at the proper tenion, if too tight, you won't be able to lower the idle. you may have to make adjustments a few times to get it right.

If the bike starts up and the idle speed creeps to high revs all on its' own, this indicates an air leak somewhere between the center throat of the carb and the cylinder head. This is normally a rubber seal or rubber manifold that is old, hard and cracked. I am sure the carbs need to be cleaned, remounted and adjusted. This is a nightmare for the novice mechanic. Replace all rubber fittings and seals including hose fittings and hoses.

either a vacuum hose has come loose or is worn/cracked, or you might have a leaking head gasket.
when engine is running at a normal idle,... spray some carb cleaner around hose fittings and the intake manifolds one carb at a time..if the idle goes up..there's your problem.

the thumb screw is not your problem adjust it at the carb

I also own a 1980 GS550L that had a similar problem, first thing I did to fix it is to add a can of seafoam to a half of tank of gas or less. The bike can run on pure seafoam if needed. Let it run for 3-5 minutes and shut if off. Let it sit for another 5 minutes then start the bike and take it for a ride. After 20 or 30 miles go ahead and fill the tank up with gas. Within a tank or so you should start noticing it idleing better and more power. On the GS550 the choke self adjusts as you use the throttle. There is no need to push it in the rest of the way. Even if you are extremely hard on the bike opening the throttle all of the way it will never go all the way in unless you push it all of the way in. I own two GS's and niether of which prefer to idle if I push the choke all of the way in. Once I did this and learned just to leave the choke alone and let it stay where it self adjusted as I rode the bike it has never stalled since at a light. You should be able to pick up a can of seafoam at any local autozone or advanced autoparts. Most likely your idle circuit on the carb is currently gummed up and the choke circuit is all that is that is working. Myself and freinds have used Seafoam to solve this problem and just about anything with a motor that was parked with gas in for an extended amount of time without any stabilizer added. It's well worth the $8 versus pulling the carbs apart.