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1980 gs550 carb problems missfiring at 4500

  • Thread starter Thread starter Mjaven
  • Start date Start date
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Mjaven

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I bought a used 1980 gs550l . The carbs were removed when purchased. After cleaning carbs and reinstalling them there is a problem with missfiring above 4500rpm only when driving. Will rev up fine when not moving. If I crack the throttle when driving and backoff of it will run up to about 6k


Now found out that the plugs that were over the pilot jets are missing. Was wondering if that would make it run super rich?? All the spark plugs look the same which is dry but black and sooty. I already replaced the spark plugs, orings on needle valve , set float height, checked that suficent spark is present, stator and regulator were fried so they were replaced and charging is fine now 14.5v at 5k. Also done a compression and leakdown test and every thing looks good.

Will also replace the intake orings even though at this time doesn't appear to be any leaks. Also was wondering the carb boots on the air box the two inside ones seen too short and are extremely hard to stretch over the carbs and want to slip off when tightened??? Seems that since they were the carbs were off they may have shrunk up a little.
Been pulling my hair out so any help would be appretiated
 
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It's critical to make sure the airbox is sealed properly. Sound like you need new airbox boots. The bike will not run properly unless the air filter and airbox is in place and every thing is sealed. And yes, you need those plugs over the pilot jets.

Regarding the rich condition, sounds like the float height may be too high or something is leaking. GS bikes are lean from new so rich running indicates a problem.

Good luck.
 
pilot jet plugs are essential for a proper operation of these carbs

unless you are referring to the caps on the top of the pilot mixture screws - they are not essential
 
Another confirmation here.

The rubber plugs in the float bowl that cover the pilot fuel jets are mandatory. With them in place, all fuel for the pilot and needle jets is drawn through the main jet. Without them, fuel can also be drawn in from below the pilot jet, meaning it is unregulated. This will affect all the carb circuits; idle, pilot, needle and main.

The metal discs over the idle mixture adjustment screws should have been removed when you cleaned the carbs. One, this allows you to remove the adjuster screw and its o-ring, and, two, it allows you to adjust the screw for proper mixture when you put it back together.

.
 
Really nice to hear the plug covering the pilot jets are so important. When I cleaned the carbs there were no plugs present, wish people would just leave things alone. The long hours of head scratching because of this. During a test ride I figure I got just about 25 miles a gal. I set the float level, vent hoses, vacuum fuel valve, and choke. So when all the plugs looked black and sooty didn't know where to turn. Bike runs ok to about 4500 rpm and then it's like thats all it got.

Will order complete set of o rings for carb and intake. Also will soak the carb boots to soften them up. Any tips on reinstalling carbs??? I slid the carbs into the intake first but then on the air cleaner ones the midlle two are almost imposible to even touch or get a hold off. May have to replace the two inner air cleaner boots as they seem a little shorter than the outer ones. When I get them on they are just barely long enough.
 
its a real wrestle putting the carbs back on even when all the rubber is soft let alone when its not
people claim it gets easier the more you do it but i didnt really experience that :o
 
Just ordered complete o ring set for carbs and large ones on intake, new screws, pilot jet plugs and while in there replace the float valves and seats. Will keep you all posted on my progress. What is the recomended float level, I believe it is .84-.92 in.? Thanks again for the help you guys are the best!!
 
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Mjaven said:
Just ordered complete o ring set for carbs and large ones on intake, new screws, pilot jet plugs and while in there replace the float valves and seats. Will keep you all posted on my progress. What is the recomended float level, I believe it is .84-.92 in.? Thanks again for the help you guys are the best!!
Click to expand...

Check here... http://www.thegsresources.com/gs_carbrebuild.htm
 
The rubber plugs are mandatory? I could have sworn the consensus was that they weren't important. Not arguing, just puzzled. I had the same symptoms and posted them up, but didn't ever mention the fact that the rubber plugs weren't there. Where can you buy some replacements?

I swear. I've been reading the GSR for months and never saw that the rubber plugs were important at all. I must be losing my mind.:-k
 
fishman, you never read about those plugs prolly because of everyone's assumption that they would be there, like the jets, etc are

there is a set of plugs on ebay right now!
 
The pilot jet plugs are also available on Partsnmore.com they are $6.00 for all four and the inlet needle and seat are $8.00 each. There is a $35.00 minimum order and shipping is only a flat $5.00. Very fast shipping have had good luck with this company in the past.
 
I replaced all the o rings on carbs and intake, also the missing plugs over the pilot jets and new needle and seats. Now the bike runs as it should. Will sync the carbs when I get a chance, do have the vacuum gauges with the dampers.
Thanks to all for the input!!!!!
 
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