AKBLACKLEY@aol.com wrote:
BIGGA SNIP!
>
But the biggest factor in curing the stumble was to
> modify the throttle linkage so that the secondary butterfly would open sooner.
> On the stock carb when the secondary opens there is not enough fuel in the
> main circuit to compensate for the sudden rush of air volume, and it
> momentarily leans out, hence the stumble. By increasing the overlap by opening
> the secondary butterfly sooner air is moving past the jets in the second
> barrel and the fuel is there when you "step on it". The result was to
> eliminate the stumble.
Sounds backwards to me. That temporary lean condition when the
throttle is suddenly opened is common to all carbs. That's what the
accelerator pump is for. It squirts in some gas to compensate for the
temporary lean condition.
Some carbs, like the Weber downdraft that came on my Fiat Spyder, have
a vacuum-operated secondary butterfly. Even at full throttle it won't
allow the secondary butterfly to open until the engine revs up enough to
take advantage of the extra throat area. The idea is to eliminate the
stumble caused by the driver when the throttle is suddenly opened at low
RPM.
Now I'm beginning to wonder about some of our driving techniques.
CR
|