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GS550 1977 accelleration problems at high throttle when under load

  • Thread starter Thread starter xxmagnus
  • Start date Start date
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xxmagnus

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Hello everyone, i just registered here on this forum, hoping you guys could help me out.
I have recently bought a gs550 1977 mod with the quad vacuum carbs, and im trying to get it in good running condition.
I have it running well at idle, and it performs well when not under heavy load (such as uphill or high speed) especially when i can coax it into high rpm,when i hit 6k rpm or higher it runs great whatever throttle setting. With full or close to throttle under load engine rpm slowly decrease like if the engine gets to little air/fuel.
I have cleaned and checked the carbs for leaks, adjusted fuel/airscrew to org
Specs,cleaned the airfilter and sprayed new airfilter oil,
sealed the airbox,
changed intake boots orings,
changed battery and i have ordered a new airbox boot(one damaged but seems to seal), and getting 12v the places ive checked. The bike has a 4in1 exchaustand electronic ignition mounted.
Its my first 4stroke bike, im a student at this time and im planning to use this bike as dayly driver.
I have some mecanical knowledge but mostly related to cars and single cylinder 2strokes, any help is much appreciated.
 
"....gs550 1977 mod with the quad vacuum carbs, "
Is this a typing error ? The 1977 had VM carbs not vacuum.
have you checked your petcock for good fuel flow? Carbs might be running out of gas as you load them?
 
Do you have an inline fuel filter? Have you stripped and dipped the carbs? Have you adjusted the valves? Did you over oil the air filter?

Just some thoughts.
 
Thanks for the quick answer, the frame number says its a 77 but i suspect that the engine might be from 79 parts bike. I have had the fuelcock open and cleaned it and there seems to come a good amount out of the hose when i tested it afterwards.I have also cleaned the fuel filter. Is there a way to measure if i have the correct flow!
 
Can you post pic of your carbs? Maybe you have a1980 engine. You mean you cleaned the in-tank filter? These critters don't seem to like additional filters.
 
I have inline filter, overoiled the air filter first time, then cleaned it and tried again with less.
I didnt dip the carbs because i was afraid to damage the float holders if i tried to take the float off and didnt want to damage float with the dip, so i removed all jets,dipped them and blew them clean.
Havent adjusted valves yet, im currently trying to figure out were i can get the right tools to do it but its next on my list when i have new gaskets and the tools neccesary.
 
okay. Ill try without inline then. Give me 10min ill go take a pic
 
Yep, inline filters of the wrong type can cause flow issues. I still don't hear of any carb cleaning nor any valve adjustments. Nor do I see anything about vacuum syncing the carbs.
 
You have CV carbs so the engine should be an 80+ model unless someone did some very creative intake plumbing. I do see some worm gear hose clamps that aren't very stock. Also not very reliable.
 
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Im just trying to take things step by step, im learning but this is my first real mc, please have patience with me:)
Do you think i should adjust valves and vacum synch them before i do anything further?

Edit: have bench synched them.

Edit2: one of the carbs had one of the float holders broken and glued back on, this is why i didnt want to risk breaking it again trying to remove floats to soak completely. float height seemed ok when i did basic measurements.
 
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That would be the first steps to getting the bike back in good working order. If you haven't done it yet, the a complete strip and dip of the carbs may be in order as well.

Here's a site with tons of information for you:
http://members.dslextreme.com/users/bikecliff/

You can find the CV carb rebuild tutorial there along with the valve adjustment procedure.
 
Thanks, ill try do those things then. Do you know any recommended parts sites for gs in europe?
I live in the Faroe Islands and it is hard to get parts locally.

Mid range under load is the problem, sorry if i wasnt clear enough. It runs well from idle to around 4000 and very well from 6-7000+ (this is why i was hoping there was a quick fix for it, i dont understand why it runs great at very high and low rpm)
 
"... It runs well from idle to around 4000 "
I'm a slowpoke ,so that's midrange to me! Others near you will have part sources ideas.
 
Aha, thought midrange was from 3/4k + seems ive got a lot to learn..
 
These bikes are designed to stretch their legs at higher RPMs. Look at your tachometer and see where redline is. That will give you an idea of where these engine should like to run.
 
Could be the 4-1 exhaust causing the dead spot in the midrange, especially if no jetting changes have been made. You mentioned cleaning the jets, did you happen to verify the size as compared to stock?
 
I will check when i try strip and dip them. (going to wait until i have the replacement airbox boot).
Is the size stamped on the jets?
Yesterday i discovered a leak on the exchaust in the joint between the muffler part and manifold part of the pipes, ill get some exchaust paste and try to get it fixed, read that open pipes is bad, maybe the leak is part of the problem.
 
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