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79 gs550 won't take throttle

  • Thread starter Thread starter lrburke
  • Start date Start date
L

lrburke

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Hey guys, I just completed a complete carb overhaul on a 79 GS550E. I completely separated the carbs, soaked them in heated solution, replaced all o-rings with the Cycle O-rings kit from Robert Barr and set the float heights to 24 mm with the float bowl gaskets removed. I replaced the o-rings between the intake and cylinder head as well. The exhaust is factory and so is the airbox. The exhaust has a few holes in the mufflers which I know is a no no but I figured I could at least get it to run ok even with that. I set the side air screws to 2 turns out and the fuel screws to 1 turn out since someone had moved them from the notches that were there from the factory. The bike started right up with the choke and had a good fast idle. I let it warm up for a couple minutes and killed the choke. the bike seemed to idle ok but it absolutely refused to take throttle. I know all the air jets and the main jet passages are clear because I use a water pick to verify the cleaning. Don't worry I blow all the water from them! I haven't checked the points timing yet but plan on doing it. I am using an auxillary fuel tank with gravity feed so I am sure the bowls are all full. I also plugged the vacuum port on the #3 carb for the vacuum fuel valve since I am not using it at this point. All 4 pipes are getting hot at the same time. Compression is pretty even across the board. I hope it's just an air screw or fuel screw adjustment. Oh I forgot, It is real slow to return to idle which I know is a lean condition. I have rebuilt tons of street bike carbs but this is my first set of pre 1980 VM's. Does anybody have any ideas I can try? I am almost sure the bike is real lean. The jets are factory sizes. If you need any more info let me know. Thanks guys!!
 
Are your carb to head boots in solid, non-leaking condition and did you replace the o rings on them?

Plus might be worth tapping the float bowls - you might have one or more sticking floats.

Your symptoms sound too severe to just be an incorrectly adjusted air / fuel screw - they really only have a significant effect on very low throttle openings.
 
The intake manifols are in beautiful shape and the o-rings I put in were Viton and had a slightly thicker cross section so I know they are sealing excellent! There is no fuel leaks from the overflows even if I leave the fuel valve in the prime position. I set the float heights to 24 mm without the bowl gasket in place and I even make sure both halves of each float are the same and not twisted.
 
I'm having the exact same problem with my 79 550 too. Starts right up on choke and returns to a steady idle after revving. Cylinders 1&2 are running hotter than 3&4 though. My plan is to go through the carbs again and look for any blocked passageways. My points and plugs are new and compression is acceptable. I'll be watching this thread closely. Good luck to the both of us.
Willie
 
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