SOHC.co.uk Forums > CB750
NGK plugs
Pauarc:
What have you got the air screws set at now martin6
Martin6:
I started at 1 out. It was best for a decent tickover at 1200 to 1300 rpm. No.s 3 and 4 plugs were fine. No.s 1 and 2 were sooting up, particularly no.1 and after 30 or so miles I was noticing some hesitation on low throttle. I moved 1 and 2 only, a further 1/8th out. No.2 plug was then fine. No.1 was still sooty, but not as bad as previous. I then came out a further 1/8th on No.1.
However, I don't think the specific settings are the key, it's the process. If the jets and passages in the carbs are good and fully clean and float levels good, boots tight on the manifolds and airbox and the bike rolls on nicely when you’re more than, say, 1/4 throttle, then fine tuning of the air screw is where I'd start. Idling and in traffic, even at 40-50mph at low to mid revs, that's what's in play. 👍
Martin6:
Just to add. I didn't vacuum sync the carbs, but I did spend a bit of time getting them working evenly on the workbench, once they were all back on the gantry. One little trick is, once they look good, check there is no looseness on the top of each slider. Just wobble the top of the spindle, where the adjusters are, with a finger. If one is more loose than the others, then it has not quite seated down and is a little higher than the others. Not very well explained, hope you get my drift.
Pauarc:
I will have to try 1and 1/8th and see they are all at 1 now which gave me a tick over of 1000 carb have been vac sync but they are all sooty
Martin6:
Nothing to lose by giving it a try and a nice excuse for a run out in the sunshine. 👍
I have no science for this, but I prefer a marginally higher tickover on my old bikes. Maybe helps oil circulation and battery charging, but I feel it puts less strain on the chains as well, as there is momentum to help keep everything smoother. Quite possibly it's rubbish, but I feel happier! :)
Not much extra, but I've set mine around 1200 to 1300 rpm. Still plenty of engine braking on a ride.
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