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Doms CB550F1 project
K2-K6:
--- Quote from: McCabe-Thiele (Ted) on October 03, 2024, 08:14:53 PM ---Why don't you start a new post yourself under tricks & tips or do you want me to do an opener?
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I don't mind Ted, conscious of not wanting to muck up Dom's project thread, but obviously it'll be useful to have discussion containing this topic.
I'll start one in the anorak section and see how we get on.
DomP:
Im now beginning to realise how much I don't know or understand about carburetors, thanks again chaps, I need to read that all over again slowly to try and get my grey matter around it all. Much more going on than I thought.
Laverdaroo:
Phones always on Dom if you need confusing or just need a rant or even just to offer a theory mate
I know how frustrating it can be buddy
Sent from my iPhone using Tapatalk
Sesman:
--- Quote from: K2-K6 on October 03, 2024, 08:09:51 PM ---
--- Quote from: Sesman on October 03, 2024, 06:41:48 PM ---Appreciate the “hanging idle†discussion, but does this explain sooty plugs? I thought the idle jets played an insignificant role above 1500 rpm or so.I appreciate there is an element of transition phase.
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I'll try to pick the right wording to describe what their influence is.
Its situational rather than hard rev band or throttle position. This because the engine is responding to volume of ai, while the carburettor responding primarily to vacuum (the drop below atmosphere via venturi design) therefore it'll flow differently for different situations.
Example is if you rev the engine then drop the throttle instantly/fully, the air volume stops but the vacuum now climbs as the rpm decays according to flywheel energy. That provides a spike in fuel with the slide closed, making it temporarily rich which helps to quench combustion, finally to recover as these two influences equal out. All in a very short space of time. Failure to do that by having restriction in delivery jet, then it'll go lean, relatively, and promote "hanging" rpm.
Anther example .... if you're approaching a long sweeping bend and go down a couple of gears, throttle off to near closed, then say it's running 5000 rpm that'll be pulling tgrough the idle jets as vacuum is high, this facilitates it going immediately you then open the throttle, if it didn't do that you'd get a flat spot up there that's really annoying as initially it would be lean. So a much higher influence than most would suspect.
It's also why you get popping on overrun if there's an exhaust header leaking air into system. The fuel that's in excess from moving towards rich with throttle closed passes into the exhaust unburnt in some quantity, availability of leaked air then brings that back to combustible in the hot exhaust pipe, and so you get popping from air leak but supplied by excess fuel from idle jets working correctly.
I do think it needs more dedicated thread that can be referenced rather than difficult to search within another topic.
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Err….sooty plugs?
DomP:
--- Quote from: Laverdaroo on October 03, 2024, 09:51:50 PM ---Phones always on Dom if you need confusing or just need a rant or even just to offer a theory mate
I know how frustrating it can be buddy
Sent from my iPhone using Tapatalk
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Thanks Roo, you're a gluten for punishment mate😂
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