SOHC.co.uk Forums > CB750
Bogging down.
Nurse Julie:
Blimey, that's running lean. You will burn a hole in your pistons and burn the face of the valves if left like that.
K2-K6:
Good news that you've got it running more as you want it.
I'd agree that it's a little lean, but not drastically as the earth bar is "milky coffee" tone.
Definitely fit ngk 9 grade plugs to bring the tip temperature down. They have wider heat transmission path to more easily get the heat out of and away from the electrode. It's this that ultimately causes a holed piston as if it gets too hot then it ignites the mixture prior to timing point. Classic "pre-ignition" that you can't feel until it's too late.
With the needles up at maximum you've no more to add on mains so it would look wise to go up to 110 jet size that would give you more safety with the needles set as they are.
That should give you a decent baseline for longer assessments to be made along with reducing risks.
K2-K6:
--- Quote from: Oddjob on May 14, 2020, 11:02:56 PM ---Does the bike have red or black NGK plug caps fitted?
If it does those are the wrong type plugs.
--- End quote ---
I feel it's beneficial to run both cap and plug as resisted to help burn a leaner mixture and gives more margin against the effects of detonation.
As it's non standard intake tract then setup is not necessarily going to follow std manual specification.
brodsord:
--- Quote from: K2-K6 on May 14, 2020, 10:59:30 PM ---Good news that you've got it running more as you want it.
I'd agree that it's a little lean, but not drastically as the earth bar is "milky coffee" tone.
Definitely fit ngk 9 grade plugs to bring the tip temperature down. They have wider heat transmission path to more easily get the heat out of and away from the electrode. It's this that ultimately causes a holed piston as if it gets too hot then it ignites the mixture prior to timing point. Classic "pre-ignition" that you can't feel until it's too late.
With the needles up at maximum you've no more to add on mains so it would look wise to go up to 110 jet size that would give you more safety with the needles set as they are.
That should give you a decent baseline for longer assessments to be made along with reducing risks.
--- End quote ---
Thanks K2,
Yes I’m going to order the jets tomorrow and the 9 grade plugs you’ve suggested.
I’m happy that it’s on the right track anyway
Sent from my iPhone using Tapatalk
brodsord:
--- Quote from: Oddjob on May 14, 2020, 11:02:56 PM ---Does the bike have red or black NGK plug caps fitted?
If it does those are the wrong type plugs.
--- End quote ---
Yes it has the black plastic ngk caps Oddjob.
Sent from my iPhone using Tapatalk
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