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carb runs perfect until 5000 rpm

  • Thread starter Thread starter stanski68
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stanski68

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1980 GS550T, CV carbs, New Petcock, carbs cleaned 4-5 times, tank cleaned out, I put 102.5 main jets on 2 inner cylinders, I am running 2 pods, K and N specific for my year. Standard pilot jets.
My problem is that it will only run on prime, once i get it started, which is hard to do, it will idle and run perfect until 5000 rpm, and then it just stops and starts bogging down, like I said if I short shift it and run around town it is perfect until 5000 rpm, I do not have the carb vents hooked up, it seems to run worse with them on. The choke does work. It revs nice in neutral.
I cheked the plugs and they are all on the tan/lean side, pretty equal on all four cylinders. I have not raised my needles. Is that my next step?
I have never done that on any bike before. Any help will be appreciated.
Thanks, Stan
 
Good chance the bike hasn't been jetted right for those pods. But I don't know why the bike only runs on prime, especially when the petcock is new.
If your petcock is the type with a screwdriver slot adjuster and only run and prime positions, BOTH positions require vacuum to initiate fuel flow, so it shouldn't be a bad/cracked vacuum hose, nor would it be because the vacuum hose has been hooked up to a vent nipple instead of to a vacuum nipple. If either of these common mistakes were happening here, then BOTH run and prime positions should give the same results.
But if you have a new petcock that requires vacuum when on run, but requires NO vacuum when on prime, and it only runs in the prime position, then you DO have a bad hose or incorrect hook up.
You have to first be sure you're getting correct fuel flow through the petcock to feed the carbs.
Have you compared the new petcock to what your model uses? What does it look like? Are you sure it's the correct type? Have you checked/cleaned out the gas cap vent? Very important to flow.
Your over 5K problem could be a result of the same fuel flow problem. Right now, it sounds like you're not getting enough fuel.
 
Ok I Re Cleaned My Carbs This Time, Taking Off All The Bowls, Needle Valve And Seats, They Came Out Hard An I Have Alot Of Rust Debris I Put It All Together And The Bike Ran The Best It Did So Far .....around The Block, Reving To 7-9 K, I Idles Fine .......but Gas Poors Out Of The Vents And The Overlow Hole In The Back Of The Carb, On All The Carbs, Those Adj Screws On The Back Of The Carbs Are Turned All The Way In ( If They Ard Adj), I Did Not Change The Float Levels Ever, I Unhooked The Main Gas Line And Ran It Unhooked And Leaked Gas All Over My Driveway... So I M Getti G, Gas Alot Of It Help,!!!! All Other Carb Work Will Be Peanuts After This One....
 
Rebuild

Rebuild

Get a K&L rebuild kit for your carbs and replace your float needles and seats. Check your float adjustment when done.
 
Well I Lower All The Float Bowls And Now It Only Leaks From The Right 2 Carbs And It Runs Alot Better. I Guess Those Need New O Rings And Needles/seats On Those Carbs.
 
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