I have another one for you!
I am currently copying some of the parts of
different carbs to cobble together my own design. I found info that the
slide carbs with the flat ground needle - have a needle size of 1/8" (
3.175mm) and are ground to what appears to be 'half' their
original size at WOT. My needle stock is 3.18mm, with sliding
tolerance, the needle seat/ jet is 3.23mm
That is the sized used for a 38mm carb and I
was wondering if the 44mm carb might need a bigger needle, but I don't know
how to calculate the main jet size/ fuel flow.
I have 13.1936 lbm (min of air) and 1.043lbm
(min of fuel) at 12.65:1 fuel ratio, at 7,500 rpm (WOT).
Can you show me how to work out the main jet
size please, I just need to know if I'm in the ballpark or need to go up in
needle size, if the depth of the grind exceeds 'half' the needle size at
WOT.
George (down under)
When we had SUs, we put motor oil in the slide dampers, and filed flat
spots on the back of the needle to change the fuel supply,and raise and lower
the needle in the slide. Most Race car stuff is just wide open with good
transition from zero throttle to wide open suddenly with no missing. Aircraft
is easier yet with 98% of the time at wide open, with lots of time to
write down O2 readings and EGTs to make changes later, or tailor your leaning
system.
Lynn E. Hanover
Lynn,
I figure I will have to do some small mods to the needle, as I progress.
I was concerned about the starting point ( idle) and finishing point ( wot) -
I have revised my figures and feel now confident that I will have enough fuel
flow to make necessary adjustments.
It took me 10 minutes to make the one needle, if I had to make several
more it's not a biggie. Even if for some crazy reason I run out of thickness
on 1/8", I can just step it up to a slightly bigger needle with less
grind depth.
My design allows for continuous adjustment as the throttle opens, so I
shouldn't get into trouble by running too lean.
I plan on using a O2 monitor to monitor the mixture at different RPM's
.
I'm going back to the half circle slide cut-out to maintain a more linier
adjustment - it appears the better ones are using that method.
Lynn, tell me why they use a notch on the slide. I have my own
opinions, but they may be totally wrong.
George( down under)
No virus found in this incoming message.
Checked by AVG Free
Edition.
Version: 7.5.488 / Virus Database: 269.13.33/1034 - Release Date:
27/09/2007 5:00 PM