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CB500/550 / Re: Plugs fouling at idle
« Last post by K2-K6 on Today at 09:40:32 AM »For me the question is formost: can I indeed compensate the needles clip in 4th groove by adjusting the air screws to two turns out, like that American Honda specifications booklet suggests or should i return to the European set up with needles clip in 3rd? I have always had my doubts about that US booklet and I therefore volonteered to experiment.
They are going to compensate in different ways, although overlapping in their effect, the two changes that is.
Lifting the needle iis going to give a response in fuelling curve in roughly a parabolic curve being nil or low change at closed throttle slide ... also nil at full open, with increase in fuel through that curve region.
Essentially raising the equalised air fuel ratio throughout the mid range of slide position by placing the needle higher in that air controlled slide movement.
The change in idle jet circuit will not shift the maximum flow without change to the jet number .... but will give less fuel at idle by opening the air inlet via the screw .... then reach maximum flow for that circuit (conditional on that jet number) further up in the vacuum range of venturi flow.
Longer "slope" response from idle circuit, meaning it doesn't ramp up /accumulate fuel increase in quite such an steep response as having the screw further inwards.
This may give you flat spot just off idle when lifting the throttle initially, it can also give problems at idle in consistency as it requires the slides to be set lower on "master" rpm screw, making it potentially out of range in vacuum specifications listed in carb balance. Sometimes this affects throttle response in rolling the power on and off as the vacuum gets too high with closed throttle when closed with revs higher .... feels a little "sticky" and non linear with more severe engine braking affect on closed throttle.
but all of my bikes apart from my 400F (which came with Boyer Bransden Mk3 when I bought it in 1985 and still works OK) will be fitted with the standard arrangement. I think it depends on how many miles you will be covering... not a lot in the case of most classic bikes. The standard ' Kettering' ignition system on these bikes works well ...so if it's not broken ... blah blah. When I got my 1st 400F in 1978 I designed a CDi which used the standard points and did over 20k miles with it fitted (with a couple of popped main capacitors along the way ... capacitor technology then was not really designed for CDi only valve colour TV's). I never changed the points and there was never any significant wear on the heel of the contact breakers, so the timing never went out. This was with either ND or Hitachi points though ... heard nasty stories about Daiichi points/condensers but that may be that there are lots of Chinese ripoffs around.
The point (again, NPI) about wear is, of course a really valid one and I have read about modern ignition condensers and points being rather poor quality compared to that of back in the day. Then again, I don't ride my CB400 like I did back then when one motorcycle was my only vehicle so the wear quotient is pretty low in comparison.