Have a 1980 suzuki gs550l w/o tank, got a new tank but dont know which lines go together theres four lines on the carb

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

are you sure you don,t have a shut off , should be on the left or right side under fuel tank , if you do need one go to any motorcycle shop ,be sure to get one with a off , on , reserve , the reserve is for when you run out of gas in the on position flip it to reserve and hope theres enough gas to get you to gas station

sounds like a vacuume leak

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My name is Bruce

May I suggest a trip to your local library. Cycle repair books should be in 646 stacks of reference.

Does both ports let out fuel?
If not , thn the one which doesn't could be for connecting to the intake for automatic activation for the fuel flow.

Shoot WD40 into each cylinder to get them wet.
Change gearbox oil and oil filter. Use 10w40 motor oil in the gear box. Don't use any synthetic oils, oil marked "EC", or oil with "special" additives. Stick with the major brands; Pennzoil, Quaker State, Mobil or Shell. How bad is the rust inside the gas tank? I would consider a liquid tank liner if rusted. Google “ kreem fuel tank liner “ or go to www.http://www.4secondsflat.com/Fuel_Tank_Sealer.html

• Lube chain or get a new chain (if needed)
• Lube Throttle, clutch and front brake cables
• Lube Speedometer cable
• Grease the swingarm, axle and steering stem bearings.
• Install a new battery
• Clean, and balance the carbs. This will be the problem area. They will likely be gummed up pretty good. Be sure to install an in-line fuel filter before starting the bike.

the needle and seat in the carb isn't seating. First, shut off the petcock, and drain the fuel bowls with the screw on the bottom of the bowls. Let all the gas drain out of the bowls.Tap lightly on the carb with a small hammer, the refill the carbs, see if it still leaks. if it does, you need to pull the bowls off, remove the float and clean out the needle and seat, and put it back together

u need new needel and seats in the carbs . u can check the old ones with a vaccum gauge the should hold pressure at about 5 psi

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.