Re: Idle (passive) jets

["Steven Ayres" <comwest@att.net>]

BillK=> Now where should I start
=> my adjustments with regard to
=> the idle (passive) jets, idle screw
=> and the idle air screw?

The pilot jets are not adjustable, just screw them in. They should have O
rings on them.

Setting these carbs up properly requires a fine touch and a good deal of
practice. Here's my standard recommendation on this: find a mechanic with
relevant Porsche or high-performance VW experience and a lot of it. He'll be
over 50 and expensive, and if he speaks German as his first language it's a
plus. Pay him what it takes to get your carbs in tune, watch carefully and
ask questions while he's doing it. Learn all you can about the process in
general and your carbs in particular. If you study carefully you'll be able
to keep them in tune from there, and it will be worth every penny. Without
knowledgable help, this process can be extremely frustrating, particularly
for beginners.

You know you *have* to study a good manual on this first, right? And you've
got the tuneup procedures covered, of course -- valves, dwell, timing,
fuel -- plus careful inspection of your carbs to be sure that they're clean,
they match down to the jets and they're the right ones for your car. Don't
trust *any*thing -- any detail missed here will be at least a couple of days
of frustration that nobody needs. You've also made sure there are no intake
leaks (Butterflies need rebushing? Do it now or you're wasting your time)
and your balance pipe is right.

>From there the standard method -- not necessarily the best, but where most
people start -- begins with setting the idle air screws at an arbitrary
point. Some say a turn and a half, some say two, some say three or more.
Odds are that the right adjustments will be different from that point and
and different side-to-side, accounting for specific small variances in your
carbs. You've set the idle screws and short linkages during the rebuild at
an arbitrary and dead equal slightly-open point for the butterflies. If you
didn't do that, you'll be working with six or eight variables rather than
four in getting the idle right.

Start the motor, get it warmed up, take off the long linkage arms and work
very gently with the idle air screws and carb balancer to find the optimum
idle air rates. (Track every adjustment relative to the other carb so you
don't get lost in the variables. The carbs are working more or less
independently at this point, but they affect each other mechanically through
the motor.) Then set the idle rpm and adjust your linkage arms to this.

Got a good idle now? Good start. Now you can work on accelerator pump
adjustments and carb balance through the rpm range. Chokes are last,
usually.

Other people will have other valid opinions and I may have got this wildly
wrong -- it's been several years since I set up my carbs last and I don't
mess with them when they're working right. I don't want to discourage anyone
from working with their carbs, it's important to be hands-on here. I just
want you to know it ain't simple and it doesn't happen fast, even for the
experts.

Steven Ayres, Prescott AZ
'66 Big Ghia

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