SOHC.co.uk Forums > CB750
NGK plugs
K2-K6:
Have you got plug gaps set really tight on minimum specified range ?
Pauarc:
Plugs set loose .6mm should be .6 to .7
Pauarc:
With spark tester they jump 10mm should be 7mm min I think
K2-K6:
I always find it difficult in equating "test" sparks against reality of running. I know that it obviously denotes energy expelled, but without compression and distributed fuel load taken into practical account.
If they are staying a dark colour, possibly sooting a little, then it would be reasonable to run with the idle air screw turned further out to bring it slightly leaner at very low speeds.
That won't change the ultimate flow of idle jet at it's maximum (they are effective a long way into throttle opening on these engine/carb combination) It will change the slope of fuelling from absolute base rpm (going leaner) but arrive at the same maximum flow (because of the 40 jet size) to give potentially cleaner combustion at just the lowest operating rpm range while leaving exactly the same fuelling as the throttles get wider and transition toward the main jet coming more on stream.
Martin6:
I did 120 miles today on my further out settings of the air screw. Worked well. No fouling evident. I'm guessing that as the carbs age and wear, more fuel is getting through and the additional tweak of the air screw is helping to even that out at low throttle running. Maybe give it a try?
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