SOHC.co.uk Forums > CB750
Carbs Install
K2-K6:
--- Quote from: Martin6 on March 15, 2023, 07:07:45 PM ---So, that was the dull bit. I was naughty and removed the return cable and went for a short ride. Fantastic. Handles better than I expected, sounds great. The bike is starting, ticking over, running on all 4. Idle below 1500rpm is lumpy but smooth above that and I sense it wants to pull more at 4-5,000rpm. Pretty sure a carb tune would sort it. However, the rear brake pulses badly. So that's next on the list ::)
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Assuming the carbs are balanced, the low speed setup is essentially the same as your "single Amal" in that the routine for idle mixture adjustment is to wind the screw to give highest rpm, then a bit more to see that cylinder start to falter as it gets too lean, finally back it down (richer) to give 100 rpm drop and that's the set point. You've just got to do that 4 times, one after another to set the low speed mixture as manual describes, they can be different one to another rather than set them all to X turns out . Its all fairly simple in reality.
Martin6:
--- Quote from: Nurse Julie on March 16, 2023, 08:11:06 AM ---I've taken a photo, this is our UK K2 but the routing is the same for the UK K6.
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Thanks for the photo. That's interesting. The route is the same, but my current throttle opening cable is much longer and curves out further. I have replacements on order.
Looking at the DS parts, the part no.s are different for the closing cables between K3 and K6, so I assumed they are different? Be great if they're the same. I ordered the K6 versions, so I'll give them a try. If they are wrong, I wonder if I can cut a section of the outer sleeve, to increase the bare cable length, "cut'n shut"!
Martin6:
--- Quote from: K2-K6 on March 16, 2023, 08:37:56 AM ---
Assuming the carbs are balanced, the low speed setup is essentially the same as your "single Amal" in that the routine for idle mixture adjustment is to wind the screw to give highest rpm, then a bit more to see that cylinder start to falter as it gets too lean, finally back it down (richer) to give 100 rpm drop and that's the set point. You've just got to do that 4 times, one after another to set the low speed mixture as manual describes, they can be different one to another rather than set them all to X turns out . Its all fairly simple in reality.
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I've only balanced them off the bike. The gent I bought the bike from has given me the 4x vacuum guage kit for 'Dynamic balance'. I have an itch to use it, but it could be a maze I get lost down!
All 4 are set at 1 turn out of the pilot screw, so that will need checking when I get it warmed up next. Hopefully it is fairly obvious when one of 3 cylinders starts to falter. I don't follow the 100rpm drop bit in bold? On the Amals it's also an air screw. Bike fully warmed through and I wind in until it falters then back out until stable (revs rise) and leave it there. = the point of richest smooth running.
Thanks for your help. Appreciated.
Martin6:
New throttle cables have arrived and I've installed them. What I've found is the right hand side handlebar switchgear is not seating cleanly. I think the two wires that connect to the starter button are being squashed against between the handlebar and the swirch casting. As a consequence, the two halves of the switchgear casting don't come together evenly. There could be extra pressure on the throttle slider, which may be enough to resist the throttle returning by itself, possibly. Plus, the wires are getting damaged from being pinched.
That said, I can't see how they could be routed differently. The manuals are silent!
Does anyone have (for a K6) a photo or diagram of how the wires are soldered onto the starter button?
Struggling to explain this. The starter button pushes a pin (which is inside a tiny spring). There's a white plastic part with a brass insert, that the pin pushes onto. A wire is soldered to the top of that brass piece. That is the wire that seems to be trapped when I try to screw the two halves of the switchgear housings together. On mine, the soldering looks old, but not factory. So im wondering if an old fix has introduced a problem? Should the wire be soldered to the top of the brass piece? If it is, I can't see how it can leave enough room to cleanly clamp the two halves of the casting together.
Thanks, Martin
Nurse Julie:
Martin, I think you've already said as your K6 is a UK model, your handlebars are the UK style, being lower than the USA model ones. Do you have UK K2 switch gear fitted and are the cables you've bought the short type needed for UK models and not the longer cables needed for USA models. USA model K3-K6 parts are different than UK model K2 parts and the parts aren't interchangeable.
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