John- Weber DGV- SU setup. Carbs is carbs.
My opinion- ONLY way is with the air/fuel ratio meter. Then you KNOW what's
happening. For the Weber- jets are available & it's simply a matter of
correcting the mixture at various loads/rpm as determined by driving &
watching the meter.
The engineering in Webers is quite complex- emulsion tubes, air jets,fuel
jets, neat little enrichment holes, holes in the butterflys, etc. If you want
to go nuts & have fun- get all the books on theory & tuning of Webers you can
find (I think I have eight..) and try to figure them out. I did pretty well
with the books, lots of thinking and lots of (pricey...) little brass parts.
A real "zen" process for me- probably a simple correction for an expert. It
is fun but- the books were written before the availability of modern air/fuel
ratio meters. The car ran "great" but without a meter- I really had no idea
if I had maxed out the mixtures.
In the real world- I'll bet that with an air/fuel meter and a fuel jet change
or two, you can get it running kick-ass. Or.. if you want more- read the
books AND use the meter.
I have yet to check an engine that I couldn't improve the performance of with
a simple tweek of a jet/needle. The meter tells you.
Don't get nuts about mixture at all speeds- it ain't gonna happen with carbs.
Just check hard acceleration at wide open throttle- say pulling third gear.
You want around 12-13:1 mixture.
Check mid-range cruise- say a nice 50 mph on flat, high gear, steady
throttle. Strive for around 17:1.
Check idle- somewhere on the meter- 17:1 would be great but not that
important- just so it runs nice and is not way off the meter.
That's it.
An engine will run on a godawful mixture. We have all have kept engines
running by simply pouring gasoline down the carburetor now & then or spraying
starting fluid in the hole.... That's an extreme- but it works. Just about
any carb will "run", but how good? A car can be very drivable even though it
is very rich/lean in places. That's where tuning comes into play. The closer
you get to proper mixture at various loads/rpm- the better it runs though.
Forget anyone's recommendations about jets, needles (SU), settings, etc. They
are all educated guesses but YOUR engine is different- an individual.
Get the meter and KNOW what the mixture is- then go from there.
Fred Sisson
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