Daniel Julien wrote:
>
> My '69 Datsun 1600 (OK, but I sold it 23 years ago and replaced it with my
> first LBC) used to do exactly the same thing. It had Hitachi carbs which
> were actually very close copies of SUs. It never bothered me much, either.
> I always assumed that this condition was caused by the carbs not responding
> adequately to the vacuum conditions of deceleration and supplying too rich
> a mixture, leaving unburned fuel. A check of my Haynes Zenith-Stromberg
> manual, however, indicates the opposite - it is caused by too LEAN a
> mixture, which burns more slowly, and is still burning when the exhaust
> valve opens. It goes on to say that the Z-S carb performs well in this
> situation because reduced mass (of the piston) and reduced friction allow
> it to respond immediately when the throttle is closed. So is this an SU
> thing? Any of you more knowledgeable folks out there able to shed more
> light?
>
For what it's worth....
I used to have a tuner who worked on my GSXR-750 who would jet and
adjust the carbs so the bike would burble and pop on trailing throttle.
The first time I watched him I thought he was nuts, but the mix was
always perfect. Eventually I became able to tell if it was too fat or
too lean just by the sound of the exhaust at wide open and trailing
throttle. Can't be a SU thing, since this had 4 Mikuni flat slides on
it.
Go figure...
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