32 ADFA tuning and inherent limitations

[TStark]

Its time for me to address carburation, my regrets for perpetuating another carburation thread!

So figured out I have the 32adfa. Its got a dull spot in the latter half of the primary.

Was going to begin with a rebuild kit, suspecting the power valve circuit was inoperable.
It appeared the rebuild kits did not include the diaphragm.
but after examining some exploded views, determined there is not power valve system on these models!
I’m a proficient Holley tuner, so excuse me for not using the proper equivalent Webber terms.

And it appears the 34 ADF doesn’t have an equivalent PV circuit either.

So, what circuit on these carbs richens the mix on the primary from lean cruise to high load?

The 32/36 does have a PV however.

Don’t want to waste time on a carb that leaves me flat, or try polishing a turd if it can’t be done.
Should I expect to tune this flat spot out, or will this carb always leave me flat by-design?

[bradartigue]

Webers make three transitions in normal operation. Keep in mind the term "idle jet" is really a misnomer, most operation of the carburetor outside of acceleration and true idling occur through the idle jet and main jet. You can see this typified in diagrams here: http://www.artigue.com/fiatcontent/Arti ... 124_MM.pdf

Idle stage - fuel is drawn from the mixture screw orifice

Transition stage - fuel is drawn from the mixture screw and metered orifices in the carburetor body.

Main stage - fuel is drawn from the main jets.

These stages are all tied together; the idle stage is dependent upon fuel passing through the idle jet and down inside the carburetor to the mixture screw, then, as transition occurs, the fuel is drawn from both the orifices and the mixture screw, and finally, when the throttle is full open, through neither and only from the mains through the top of the carb. The other barrel may be in a different stage of transition at the same time. (see page 32, figure 28)

An acceleration pump is fitted to Webers, which delivers an additional pulse of fuel at specific intervals. The acceleration pump is actuated by a roller resting on an arm linked to the throttle. The roller allows the pump to draw in fuel and propel it into the carburetor.

The 32ADF (note the absence of the "A" at the end) is the universal, non-USA version of your carburetor, and by looking at the materials on it (page 30 of the above, or http://www.artigue.com/fiatcontent/carbs/32_ADF.pdf) you can read about how it works and what the essential components are. The "A" series adds the USA emissions controls items; the PCV valve I think you're looking for is not mechanical in the same sense as the "D" series you mention, it is part of the christmas tree of plumbing hanging around the throttle controls on the right exterior of the carburetor.

[TStark]

Nice documents bradartigue, thanks!

Yes, that helps a lot, I will throw some time into this one now, and reset the mains if the issue persists.

[bradartigue]

Nice documents bradartigue, thanks!

Yes, that helps a lot, I will throw some time into this one now, and reset the mains if the issue persists.

That flat spot you describe is typically because the carb is either dirty (a progression hole is clogged). It could also be a faulty accelerator pump diaphragm (four screws, five minutes), or one of the jets is too small (or all, or two...) Generally speaking if it idles well and accelerates well and then goes flat you may want to go up one on the main jet.

Sometimes people get the main and secondary jets mixed up, that would cause it too.

[TStark]

Good to hear.

Backerds jets are quite likely given what i've witness so far, fuel lines reveresed, the 2" toe in, the heater blowing heat outside...

I'll give it a good ultrasonic and give it a rip.

[TStark]

Well, gave it a long untrasonic.
I found the air correctors reveresed, but the mains were correct according ot spec.

Funny thing is, it seems the engine had more peak HP with the air correctors reversed.

The dull spot at the upper primary and thunk when the secondary opens is gone, thank goodness.

But i believe this data suggests the mains are not quite optimal yet.

[bradartigue]

It is most likely tuned for mileage (e.g. factory tune) and not for anything else. It probably won't hurt to leave the idle jets as is and go up .005 on the main jets.

[TStark]

Thanks bradaetique,
New Jets are in the mail.