79 spider won't idle

[dancooper]

Hi all,
Hoping I can gain some wisdom from you fine folks. About 3 months ago my 79 spider started dying when coming to a stop. I called my mechanic and he said to adjust the idle mixture screw on the carburetor . I did that, and all was well for some time, though I think it has just masked a different issue, because now it has evolved into what I'm dealing with today. At this point the car will not idle unless choked, and even when choked it is not running as expected.

Current running condition:
from the front: https://youtu.be/u7-k4Q1jXDw
from the rear: https://youtu.be/BoxBWvJpHGQ

Unfortunately I'm in California, so I'm working with the ADHA and upgrading the carburetor isn't an option. what I've done so far, all carburetor related:
disassemble and clean all the jets
new gaskets
tested/cleaned the idle solenoid
turned tuning screws 'til the cows came home

I started with the carb on the mechanic's recommendation, but maybe it's something different altogether? any recommendations are much appreciated.

many thanks,
dan

[bobplyler]

Sounds like a vacuum leak.

[gschwab]

I had something similar happen, was in issue with the gulp valve. The internal seal had failed, and the engine was constantly getting air from there.

[manoa matt]

Specific to the 79-80 ADHA carburators, there is a white/cream colored plastic cam located under the choke housing. The plastic becomes brittle with age, and if broken off, will not idle. It may be hard to see with the carb on the car, but an inspection mirror may help. Many non-California members have removed their ADHA's and may be of assistance with the replacement part. Wetmikey recently swapped a ADHA for a 32/36 DFEV.

[dancooper]

Specific to the 79-80 ADHA carburators, there is a white/cream colored plastic cam located under the choke housing. The plastic becomes brittle with age, and if broken off, will not idle. It may be hard to see with the carb on the car, but an inspection mirror may help. Many non-California members have removed their ADHA's and may be of assistance with the replacement part. Wetmikey recently swapped a ADHA for a 32/36 DFEV.

Hi Matt, I've taken the carb out and apart a half dozen times and have never seen any plastic cam beneath the choke assembly. I also have a spare carb of the same model where I don't see any plastic pieces anywhere on the outside of the carb. can you point its location (or expected location) out on this diagram?https://www.piercemanifolds.com/category_s/226.htm

[manoa matt]

It can be seen in the photo on the right. You can just see two white bits behind the choke assembly and just above the cover plate that is labeled No. 96 in the diagram you attached.

https://shop.schiminsky.de/images/5211.JPG

[wetminkey]

Try this link, it's a better diagram of the disassembled ADHA:
https://www.piercemanifolds.com/category_s/226.htm
I think Matt refers to the plastic portion of the choke valve control diaphragm 'assembly', which can be seen just below the choke's linkage (inside the choke module) when the choke's cover/thermal element is removed.
The diaphragm and 'assembly' come as a unit, and should be replaced when rebuilding the carb.
Item # 94 in the above diagram,...
Just completed a FULL rebuild of my 28/32 ADHA carb,...
Best of luck with your's,
Todd.

[wetminkey]

This may help also.
PaulC's pictorial rebuild of ADHA:
https://drive.google.com/file/d/1DLaHYG ... PPROL/view
Todd.

[dancooper]

This may help also.
PaulC's pictorial rebuild of ADHA:
https://drive.google.com/file/d/1DLaHYG ... PPROL/view
Todd.

#94 looks to be the choke pulloff diaphragm, no?

[PaulC]

Choke pull off it is.
Dan, see your PM for the gulp valve on its way to you.

[wetminkey]

Yup. Fiat Shop Manual calls it the "choke valve control diaphragm". It's the diaphragm and small hardware assembly that rebuilds this choke control module,...purchased as a single unit. One of a couple of extra diaphragms (required to rebuild the ADHA) that are NOT included in rebuild kits for the ADFA/ADHA.
Looks like this:

[dancooper]

Matt, is that what you were referring to in your photo? just wanted to confirm because what I saw on the photo is highlighted in red in the first image, and then the second is what I see from the same angle on my spare ADHA: https://imgur.com/a/bzncU4s

Am I missing something? I'll add a photo from the carb in the car shortly. [update] added new photo to same post above.

[wetminkey]

No plastic links on the outside of my ADHA.
And I do not know what you got a picture of,...?
Check the piercemanifolds.com diagram and indicate what part/link we're trying to refer to,...