I bought the 'K' bike a couple months ago. At the time of purchase, it was not firing on #2. Since purchase, this is what I've accomplished:
1. Loose #2 spark plug wire @ boot, trimmed and fitted into the boot
2. Removed the carbs and found #2 carb float was WAY out of adjustment... was effectively shutting off fuel flow except for fuel that may pass the valve when it was sitting... explains why it started and seemed to run fine until it emptied the float bowl and #2 would shut down...
3. Leak @ fuel line entering #2 carb. Found the see-thru hose (no clamps) was not seating well on the carb inlet. Added hose clamps. Leak reduced but not eliminated. Added correct ID fuel line and clamps... no more fuel leak.
4. Set points using static method. Both 1-4 and 2-3 points were practically closed where they should have been @ .012-.016 gap.
At this point, I was hopeful the flat spot would have been resolved. Granted, it was improved (given a number of ills were removed from the overall driving/running experience). The spark plugs are all now a nice light white/tan.
5. Replaced points/condensers and set @ .014. Was thinking it was the condensers not discharging properly. Spark advance opens freely (removed the points plate when I installed the new points). The advance weights and springs do not appear to be binding/hanging up.
The 'K' has a MAC header and canister muffler. Also, the air box was removed in favor of POD filters. PO replaced the main jets.
The bike runs great 1,000-5,000 up through the 1st four gears. Then, if I'm gradually accelerating in 5th gear through 4,000-4,100, it hits a plateau. It doesn't fall flat on its face but it sort of hits a flat spot. If I put a little more accelerator into it, it runs through that rpm point. At 45-55mph and 4,500-5,000rpm, the engine is running fine (as it does before reaching 4,000rpm in 5th gear). If I were to be perfectly honest, I get a sense of the flat spot in 4th gear at about the same point (4,000rpm).
I suspect a transition circuit issue in the carb bodies. It is hitting a 'lean' spot on the point identified in my description of acceleration behavior.
I am considering re-installing the OEM air box and filter. PO said it was missing a 'lower cover'. I have the items save for the missing lower cover. If this doesn't sort the issue out, I am considering dis-assembly and cleaning of the carbs with close attention to the cleanliness of the carb bodies/circuits as well as cleaning the jets with a fine metal (#1?) guitar string.
If after the air box and carb cleaning, I still have the issue, I am thinking that perhaps replacement of the main jets was either to an incorrect main jet size or was insufficient to resolve the issue. Perhaps other jet components need replacing. Oh, PO also replaced all four needle valves on the carbs. I have the OEM main jets on hand.
A question: 550F has an air box and 4-into-1 header setup. I have a buddy that, save for installing a MAC 4-into-1 on his '75 CB550F, he didn't have to touch the jetting and kept his OEM air box. Should I considering installing the same jets that a CB550F runs (along with the OEM air box re-install)?
Picture attached.
