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Honda CB750k2 main jets
Nurse Julie:
--- Quote from: Pauarc on August 07, 2023, 08:55:49 AM ---All plugs are now running a bit on rich side
--- End quote ---
I always set mine to run very slight on the rich side rather than the lean side.
K2-K6:
--- Quote from: Pauarc on August 07, 2023, 08:55:49 AM ---All plugs are now running a bit on rich side
--- End quote ---
What that is showing is the richer mixture of idle circuit only.
Changing from 120 to 110 main jet, you'll see at wide open throttle specifically. You have to run them absolutely wide open and pulling maximum torque to assess this, nothing else will show the effect.
Its classic "plug chop" routine. Warmmup, then getting it pulling "balls out" and hauling it's maximum torque in something like 3rd or 4th gear, pull clutch, switch off, then exhamine the plugs to see what the maximum demand is telling you. Nothing else will fully inform you about accuracy of main jet mixture than that, even if you never want to ride it like that :)
Main jet size is about peak flow through that with the needle fully retracted (wide open) the taper controlling all the rest of intermediate mixture below that.
If it goes flat as you come up on the throttle in low speed with 110 installed, that's telling you it's going lean in the region where idle hands over to needle taper, hence the response you get when you turn the airscrew inward, it just brings idle mixture slope to a more steep gradient in getting the two to attach.
Now it'll show rich at low rpm use, because of this.
Raise the needle, leaves the maximum alone at full throttle broadly, but "fattens" the mid to low range slightly, and avoids the need to run idle too rich.
It's "mapping" but with a carburettor.
Pauarc:
How the plug’s looks now
K2-K6:
The colour doesn't look too far out from those plugs as far as I can see.
The ceramic collar around the central electrode is what I'd use for primary judgement, it'll probably take more lengthy run at load to see accumulated view from the outer surround near the threads.
Picture is a little blue bias, masking the yellow content (opposite to blue and significant part of brown hue on plug carbon ) to judge more accurately.
Was wondering what drives the decision to turn the idle circuit more rich initially ?
Pauarc:
It idle better about 1turn and rev up ok and good response up to 65 to 70 from stand still. It just the tic over I would like to get better
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