The carbs I have started out as 1977 tag # AVD665R with ABT stock needles.
I have a stock motor except for 4 into 1 header and the twin SU - K&N
setup. I run AAA needles with yellow springs. The AAA are too fat in the
midrange and on the top end and I will be switching to AAQ or AAT (leaner)
to lean out the mid range and top end. If you get yourself a SU manual,
they usually contain heedle charts in the back. You can enter the data
into a spread sheet and work out the flow area around the main jet as the
needle moves up. These are constant velocity (depression) carbs so the
vacuum drawing the fuel past the jet remains fairly constant as throttle
position changes.
You may not be noticing too much difference between your needles because
you are not pulling the needle to full extension when you are wide open at
near max revs. On CV type carbs I have found the greatest effect on
jetting to be changes in restriction prior to the carb (i.e. air filters
and air inlet temp etc.)
Jetting carbs almost becomes unique to each engine, where and how it has
been modified and where and how it is driven. (ps I live in cool dry air
at about 2800 ft.)
Good Luck Jetting ----> Larry
----------------------
> From: bharris <harris88@rochester.infi.net>
> To: Larry Quirk <Larry.E.Quirk@gov.ab.ca>
> Subject: Re: 1-1/2" Su's for 1500
> Date: Monday, November 10, 1997 9:09 PM
>
> Larry Quirk wrote:
> >
> > Ed wrote:
> > ----------
> > > From: Edward Hamilton <hamilton@ptd.net>
> > > To: Triumphs <triumphs@autox.team.net>
> > > Subject: 1-1/2" Su's for 1500
> > > Date: Tuesday, November 04, 1997 8:53 PM
> > >
> > > Looking to change the single carb arrangement on my '80 Spit to a
dual
> > > 1-1/2" su setup. Should anyone have this setup lying about, please
> > > contact me.
> > >
> > > Best regards,
> > > Ed Hamilton
> > >
> > Ed: incase no other listers come across with the goods, I got mine
from a
> > Spit/GT6 recycler in Whales (UK). They cost me the equivalent of
$75.00 US
> > and included all parts to attach including the manifold & filter air
box.
> > I spent $150.00 more rebuilding & having the bodies bushed with new
shafts.
> > A couple of evenings spent polishing piston chambers to a chrome like
> > gleam. I toped them off with K&N pancake individual air filters and
used
> > stainless steel allen key head fasteners all around. Use the yellow
piston
> > springs with the K&N's and expect to buy a number of needle pairs as
you
> > dial these in. Headers, compression, cam, altitude, etc. will all have
an
> > impact on what needles work best. Don't expect too much of a
performance
> > gain on a relatively stock engine but as mods go up, they sure help the
> > breathing. The K&N's give the intake a nice "honk" to match the
exhaust
> > note.
> > Good hunting,
> > Larry (SPITMAN) Quirk
> > 80 Spit
> > 70 GT6
> > 69 Spit
>
> Larry,
> In your reply to Ed Hamilton you spoke of a few sets of
> needlesand I was wondering which needles you use? I have a 76 Spit
> with.050 off the head,dual valve springs,a "fast road" cam and dual SU
> HS4's K&N filters,yellow springs and "regular"(not waxstat) jets.I've
> used 2 sets of needles AAB's and AAM's not too much differance for
> street use between the two. Just wondering what you have found to work
> for you.
> Thanks,
> Bob Harris
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