G'day all,
I could suggest a few things to add to what Les has already suggested below.
Firstly, I'd agree that the carb-balance is all-important in gaining a
smooth transition. On both downdraught and sidedraught twin Weber Alfas,
I've found that even a very slight mismatch in the throttles opening as you
accelerate gently can cause a sudden surging in the engine's output, which
might be taken for a hesitation due to a misfire during transition, when
it's not that at all.
Secondly, to adjust that balance, I've never had much luck with the usual
tube-method (unlike Les, I'm no musician!), so I have to try other ways. One
way is to fine-tune the balance for the smoothest sewing-machine-like idle,
and another is to short out the 4 plug-leads one at a time and aim for equal
rev-drop in each case. However these methods depend on the idle mixtures
having been properly set first, I believe. A third test for correct sync is,
I believe, to slowly increase the rpm from idle to moderate revs while
you're parked, and confirm that the engine does not develop any periods of
surging or rocking around, at any point as you increase rpm.
One way to put the balance in the right ball-park before you even start the
engine is to look in through the progression holes (under their inspection
cover on each carb), and confirm visually that the butterflies are in
identical positions relative to the holes, and adjust things if they're not.
And of course, if you're new to Webers (or twin carbs in general), don't
forget to make sure that the accel linkage does start to open the carbs
exactly simultaneously once the free-play is taken up by your pedal, so they
do stay in sync having started off identically with your foot off the pedal
(i.e. at idle situation).
Pat Braden's Alfa Bible gives a pretty good idea of the basic setup process
on a twin-carb Alfa - well worth a look.
I think it includes the fine-tuning of the idle mixture screws referred to
by Les in his Item 2, and indeed these probably will need some fine tuning
after the initial get-you-started settings Les gives.
I'm no carb expert, just an amateur, so if anyone finds any nonsense in any
of the above, please say!
Lastly -- Les -- your GTV! That's dreadful news. Can she be saved? And, I
hope this GTV isn't the famous LS2000, the legendary Green GTV? I haven't
seen that car on Wellington streets for years - I hope this one isn't it.
You can't possibly go to the Alfaclub's 40th in Taupo without a GTV!!!!!!
Regards all,
Graham Hilder, NZ
(1750GTV and many Alfasud)
From: Les Singh <[email protected]>
Subject: [alfa] Webers and transition from idle
If the carb s were jetted correctly to start with, I would firstly check
the adjustment carefully before playing around with jets. Try the following:
1. check the throttle preload; does the actuator spring "force" the
butterflies shut when you lift off the accelerator? Unless the preload
is present, the carbs won't behave correctly and you'll find it
impossible to get a smooth idle and transition also.
2. Which model of DCOEs is fitted to your engine? Some require the idle
adjusting screws (the 4 screws with tapered needles at the seat end) to
be backed off 2 and 1/2 turns from closed while others are backed off
only 1 and 1/2 turns. (Here we go: there's going to be a whole lot of
people telling you this is wrong!).
3. Does the idle hang up rather than settle to 800 rpm when you open the
throttle then release it suddenly? If it hangs up and comes back to
idles only slowly, your balance between the two carbs is not set
correctly. I adjust the balance by listening to the airflow tone with a
tube stuck in my ear (I'm a musician as well!). Get a musician friend to
help, preferably a blues man or classical musician and not a heavy metal
exponent whose ears are probably shot. :-).
If all of these check out, then you could start looking elsewhere. Hope
this helps.
I collected my GTV which had been supposedly undergoing restoration for
about 5 years and trailered it back. What I got what was a parts car. My
mistake was listening to "Alfisti's" recommendation and giving the car
to a body shop 6 hours drive from where I live so I couldn't keep and
eye on it. Now it's back to Square Uno. Damn.
Les
Wellington, New Zealand
Gentle Alfisti,
The 1600 is now a 1700 with Spruell's kit. New Webers don't provide
smooth
transition from idle. In the Digest's opinion, should I look at jetting or
dizzy advance? Would a stumble come from too slow an advance?
modelle105.04, 115.02
http://www.avast.com
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