This is an old post so probably wont get a response. I started with the same problem on a bike i got up in Austin. A 1975 CB550F Supersport. I have replaced, rebuilt, check so many things and still get the fine on the stand, lousy on the road issues. It will sputter to third gear and suddenly start to build speed but once in 5th it loses power and struggles. I downshift and let off the throttle a bit and then apply and will start to gain power again. Coming to a stop almost always stalls the bike. I have 110 mains and 40 pilots per classic Octane and velocity stacks. Original owner lost it and treated the bike like garbage. Found pennies in the gas tank. Carb is rebuilt. Needles set to middle notch. Replaced both coils. It has Dyna S coils of undetermined model. The rotar was on backwards and firing wrong so corrected that. Using a light to set the timing in the F mark made it worse so i adjusted by hand while it was running very carefully and improved idle but same main problem. I cleaned up some ground wires and electrical lazyness from the last owner and soldered and shrink wrapped the parts that needed it. New plugs, new rectifier, new coils, carbs re synced. But today i sprayed throttle cleaner at the intake manifold boots to the carb and it stalled while idling instead of reving up. So too much fuel. Yet turning the A/F mixture made no difference. I replaced the o-rings where the metal intake attaches to the engine and resolved the vacuum leak. Im wondering if i need to re-sync the carbs again. I have been working on this bike for a year or more trying to get it running right. I even replaced the oil pump that leaked and the head gaskets as they had a slow oil leak as well. Replaced the clutch plates and springs. Replaced the petcock, seat, signal lights with LED, headlight with Halo LED and other none engine related parts. I have lost a lot of money at this point and i cant afford to pump anymore money into it. So after my carb sync this week, if it still has problems I'm junking the whole bike. I learned a lot and one of those lessons was that buying a bike used is the worst thing ever. My first bike which i still have runs great and i fixed it up no problem but it is an 02 Shadow spirit VT750. Same mechanics except for a computer to run the fuel pump. But this CB550F is a headache. I rebuilt the forks twice due to leaking, replaced the front brake rotor twice do to a constant squeeling, rebuilt and replaced the front brake and lines also. But the stupid spring push adjuster only stops squealing if in a perfect position. This bike has been a nightmare for me. So right now, i have this stalling problem when coming to a stop and problems keeping speed/power in 5th gear. My problem sounds a lot like the original posters and i read through every post here. But im at a loss. I even re set the valve tappets. Anyone else have any other ideas before i take a sledge hammer to this pain in my ars?
