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Mike's CB550 Project
Mike_Berkshire:
--- Quote from: K2-K6 on March 15, 2025, 07:08:42 PM ---
--- Quote from: Mike_Berkshire on March 15, 2025, 06:34:44 PM ---I didn’t Ted as I have dual fuel lines from the fuel tap and I thought there wouldn’t be room. Maybe a poor decision!
--- End quote ---
If you wanted to do this temporarily even, you can buy more pipe and route down under the carbs, site the two filters there in clear space, then route back up to the carb inlets.
It could be a pragmatic workaround while you deal with getting residual unwanted bits out of the system.
All mechanical things being in order ..... it's "always" fuel restriction against air supply that gives this hanging effect.
--- End quote ---
Can I check the meaning of " fuel restriction against air supply“. Do you mean something is happening to make mixture too lean when throttle is in closed position ie in the idle circuit?
McCabe-Thiele (Ted):
Does this PDF file help at all?
Mike_Berkshire:
--- Quote from: McCabe-Thiele (Ted) on March 15, 2025, 09:28:50 PM ---Does this PDF file help at all?
--- End quote ---
Thanks Ted, it all helps. Incidentally mine is. ‘76 K2 and I also have the hollow tip cross drilled air screw in my carbs.
K2-K6:
--- Quote from: Mike_Berkshire on March 15, 2025, 08:33:54 PM ---
--- Quote from: K2-K6 on March 15, 2025, 07:08:42 PM ---
--- Quote from: Mike_Berkshire on March 15, 2025, 06:34:44 PM ---I didn’t Ted as I have dual fuel lines from the fuel tap and I thought there wouldn’t be room. Maybe a poor decision!
--- End quote ---
If you wanted to do this temporarily even, you can buy more pipe and route down under the carbs, site the two filters there in clear space, then route back up to the carb inlets.
It could be a pragmatic workaround while you deal with getting residual unwanted bits out of the system.
All mechanical things being in order ..... it's "always" fuel restriction against air supply that gives this hanging effect.
--- End quote ---
Can I check the meaning of " fuel restriction against air supply“. Do you mean something is happening to make mixture too lean when throttle is in closed position ie in the idle circuit?
--- End quote ---
Yes, exactly that.
The idle circuit, both air passage and it's paired jet act as, effectively, a tiny carburettor within the main carburettor. It gives these carb and engine the fine control necessary to have very smooth tickover and linear response as you modulate the speed at very low rpm.
The passages in tbat circuit are, by necessity, pretty small. Any impairment makes quite significant change in mixture as it's metering such tiny amounts of fuel at idle.
Ultimately any blocking of the fuel jet scuppers that fuel to air ratio that needs to be in place to work. And so, you get very annoying effects from just small or partial blocking.
I'd expect to see the fuel jets having debris in them here.
In essence if there's air going through the air control route (the screw you adjust and it's route into carburettor vehturi) but low or no fuel being drawn up from float bowl, then it'll run lean and not want to slow down sufficient to give stable rpm. They will, when set correctly, run slightly rich at no throttle idle point. Its only very small amounts of change we are considering here, frustrating nevertheless.
DomP:
So is that why I have a hanging idle yet also symptoms of running rich like sooty plugs and strong fuel smell? Sounding like another carb off job
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