Phil....
Webers are infinitely "adjustable".
While the SU (in stock config.) is a user-
friendly "utility" carb of "variable" choke
which will adjust flow to the demand of
the motor, the "fixed" choke of the Weber
will not.
You cannot expect to take a
Weber tuned for a specific application and
put it on a different motor and reasonable
expect it will run (if at all) on a different
motor, even one within the same group.
First of all, the chokes are wrong. Considering the bore/stroke ratio of the
1275 basically "matches" that of the 948,
the jetting "ratio" (fuel to air) is most likely
correct, though in terms of "quantity", you'll need to go larger are both. The
emulsion tubes may or may not be correct
for the 1275. They most likely are, but they
can just as easily not be.
Same with the aux venturies, idle jets, pump
jets and pump jet spring/stroke, despite
similiar bore/stroke ratio of both the 948 and 1275.
Now if you know a "tuner" who also knows
how to run a dyno, he can set it up for you
but considering the start point here, it will
cost you a small fortune considering time
and assortment of calibrated parts you'll
need to do this properly.
If you don't do it "properly" and insist on
running the Weber anyway with attendant
less performance/economy than can be had
by the above method....OR....by acquiring the correct kit for the application,
it can cost you big time in pre-mature bore/engine wear along with poor fuel
economy, not to mention frustration.
What would I do in your shoes??? I'm glad
you asked! :)
1. If you know someone running the "proper" DVG kit (including whether
it's of the water heated or unheated variety) on a motor such as yours, then
get the calibration specs for this application from this person and set up your
DVG accordingly. This will get you 90%+ "there".
2. Contact www.piercemanifolds.com (Weber experts who supply the various
specific stock kits for stock applications)
and explain your problem and ask them
for their help and the correct calibrated
parts for your application.
It will cost you a few bucks but it will save
you 1,000 times over in money, time and
frustration and possible premature engine
wear/tear.
Tuning a Weber is not magic, but you've
got to know something about "flow" under
different circumstances and how each circuit within the carb plays it's part,
most
especially during periods of "overlap".
In these respects....
when you don't "know", pay the expert and
be done with it or risk premature engine
wear/tear/damage. Too much fuel on a continuous basis will cause
bore-washing....
too little (especially under load) on a
continuous basis is worse by far.
But why open yourself up to either "option"
when expert help and the calibrated parts
required for your application is only a phone call away?? :):)
Cap'n Bob
Basic Frog
away???
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