Hi Dave
A review of Des Hammill's book "how to build and power tune SU
carburettors" has some excellent information on needles. It is a
worthwhile read.
Kind regards
Ed
www.vintage-sportscar-touring.ca
'65 BJ8 '89 Morgan 4/4
Dave & Marlene wrote:
> While we're on the subject, It seems that corelating carb piston/needle
> station position to engine load & speed is a major problem. How can you
> know what needle stations are actually in operation under given
> conditions. For example - large carbs on a small engine will never have
> the pistons as far open as would be the case with smaller carbs. A carb
> capable of flowing 400 cfm will not be fully open on a engine that can
> only use 300 cfm. How do you know exactly what needle stations are in
> play at low, midrange, & full power?
>
> I once tried running with the hood off & a measuring stick in the top of
> the damper to see what was happening under various loads. Not too
> successful or accurate. It would be pretty easy to do on a chassis dyno.
>
> In spite of gas analyzer readings, without this knowledge, we are still
> completely guessing on needle profiles. Very little better than dozens
> of needle trials.
>
> I think people make assumptions that the piston is closed at idle, half
> way open at some assumed midrange, & fully open at full throttle - high
> rpm. Not likely in most cases. We need the equivalent of a throttle
> position sensor to determine piston position.
>
> What's the answer?
>
> Dave Russell
> BN2
>
> Freese, Ken wrote:
>
>> Martin,
>> I read about using the oxygen sensor years ago for tuning SU's on this
>> site.
>> I thought it would be good to see if my PCV valve and the headers
>> affect the
>> mixture and the Colortune only really works at idle. I got the digital
>> readout last year. Maybe I will get the oxygen sensor installed next
>> year, a
>> bung for the front three and a bung for the rear three. But for now, I
>> need
>> to fix a burned valve. Ken Freese
>> 65 BJ8
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