SOHC.co.uk Forums > CB750
Carbs Install
K2-K6:
--- Quote from: Martin6 on March 16, 2023, 09:13:21 AM ---
--- 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.
--- End quote ---
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.
--- End quote ---
To clarify as its doing the same thing, but possibly different interpretation.
Starting with the adjustment screws as you've set them (1 turn out) turn further out and revs should rise as it will get leaner on these carb. Keep turning very slowly and small increment, then that cylinder should go too lean and you'll just hear it start to falter/miss a little (this confirms you're at balance point of decent mixture) now turn the screw back inwards slowly until the revs just start to drop (honda say this should be 100 rpm drop) which makes it's just a little richer to finally set the position there.
Each carb can have a different final set to give even cylinder burn, this is the low speed synchronisation method for these carbs.
If you now put the vac gauges on them, they should show as in tolerance noted in the manual, not needing any more adjustment.
Martin6:
Thanks everyone. Switchgear's all back together and a nice snap on the throttle. Now for a quick run, so i can tweek the carbs. :)
Martin6:
Happy with the run :D. Not happy with the corroded spring on the starter button. A Google search took me to Julie's ebay store. Replacement on order. :)
Martin6:
My starter button was very loose and wobbly and the starter actually came on when I pulled out from getting fuel. It was ok if I pulled it back out, not a long term solution. On inspection, the spring around the button's brass plunger was in several pieces inside the switch and doing very little. A new button and spring arrived today (thanks Julie).
I've spent about 6 hours trying to get the starter switch back together. It looks like the one in Julie's picture and the button is identical to the original, so the new parts are right. I cannot get the two contacts into the switch whilst the button and spring are in there. I've managed to break the solder joints a couple of times trying to get it assembled. How I laughed...!
Is there a knack to this?
Nurse Julie:
Are you trying to do it with the switch gear still on the bike? The knack is to take the switch gear off the bike and do it at the kitchen table with a cup of tea 😁😁😁😁
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