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RFVC tune up problem

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by t_mike, May 12, 2009.

  1. I have a CBX 125 Custom that was never imported to Australia, in fact I don't think it was sold anywhere that has a language that uses our alphabet. This makes even the net a bit useless to find info. I'm a mechanic, but not a bike mechanic, and I am doing the work myself.

    The bike has a twin cam/carb version of the Honda RFVC motor. My problem is this, anything over 1/3 throttle and the thing dies. I've cleaned out both carbs with carb cleaner and compressed air, and all looks as clean as. The carbs are operating progressively as they should, but I'm unsure if the opening point of the secondary is correct, with no tech info I have no factory settings available to me. Both sliders hit full throttle at the same time. I don't have the correct ignition box in it, but I don't see that as the problem, I've had it to 9000 rpm on a downhill with no misfire. It does feel like fuel starvation. If anyone has any experience with one of these family of motors with twin progressive carbs, and can offer any suggestions, it would be appreciated. The whereabouts of any tech info would be good too.

    Thanks in advance,
  2. With only a few visits, and no replies, I don't know if anyone is interested, but I'll keep updates going just in case.

    Today I had a few spare moments, so I decided to disconnect the throttle cable that operates the secondary carb. This is done in a little box under the fuel tank on the left side of the bike. It has a dual lever set up in it that allows the cable from the grip to pull on a lever assembly that operates 2 separate cables that control the opening of both carbs. The speed at which they open is fixed, but the commencement of the opening of the secondary is adjustable. The secondary carb has no low speed circuit, only a needle jet main circuit. The idea was to disconnect it and see how the motor runs on just the primary carb with it's low speed (idle/progression) circuit. I allowed the motor to warm up and adjusted the idle speed to about 1200rpm, then adjusted the idle mixture to the point of smoothest running. The result was that the engine ran much better, allowing me to use as much throttle as I wanted. However, if I gave it sudden full throttle from idle, it would hesitate for a second or 2 before reving. All this was done in the garage with no load, and I didn't allow the engine to rev above 6000 or so. This leaves me with two questions, firstly, is the secondary solely responsible for the unwillingness to work above 1/3 throttle, secondly, is the flat spot in the primary partly or fully creating the problem when the secondary opens?

    Any suggestions would be greatly appreciated, and if anyone knows where I might be able to get a schematic of the circuitry of these carbs, that would be great too.

    The adventure continues...