fast idle won't come down - 1979

[o0sara0o]

Getting an old 79 restored. Carburetor may be completely out of adjustment. Vehicle starts finally with lots of cranking, and until recently seemed to idle well. Now, won't come off fast idle. What's the procedure for tracking this down?

[So Cal Mark]

you could start by removing the air cleaner lid to see if the choke operates

[bobplyler]

Mine had a fast idle(1800-2000) problem for about 15 years. I just lived with it, as I was never able to fix it. The only thing that fixed it was changing carbs.

[majicwrench]

Tis a simple carb. Is cable too tight?? Ya gotta look, what is holding throttle open?? Fast idle cam?? Got a big vacuum leak?? Older Fiats have a fast idle device, not sure if 79 does, something is holding throttle open, ya gotta look. Keith

[blurple124]

My fast idle was a result of a gummed up throttle linkage spring. I just sprayed it with some PB Blaster and it worked like a charm.


I have a '78 with a 32 ADFA.

[TX82FIAT]

Had a 79 back in high school that idled fast. I tinkered with that carb for a couple years adjusting and cleaning it. Something just escaped me when trying to fix it until I finally picked up a carb rebuild kit and fixed the issue one month before I sold it. I still cant tell you what caused the issue.. gaskets, dirt, diaphragm, valve(s), needle? Rebuilding the carb was a PITA for me. I think it would be a lot easier to do today as you can pull out your smart phone and take pictures of all the linkages, screws, hoses in order of dissasembly.

Try taking it apart and cleaning with carb cleaner and a soft brush. I would stay away from a hard wire brush.

[majicwrench]

No point taking whole thing apart, fix the problem.
' Keith

[o0sara0o]

Where can I find a well-labelled diagram of the various cams and linkages on this Rube Goldberg carb? Our shop manual does not give details.

All is fine with the throttle linkage. Finally we pulled the whole carb, which allowed good view of underside of fast idle diaphragm. It actuates a couple cams, one of which was flapping in the breeze alongside a spring that seemed like it should have been connected to it. Plus, there was a linkage about 2 inches long attached to the cam that was also not connected to anything, and there wasn't anywhere around that looked like it was missing a linkage.

You see, I could REALLY use a well-labelled diagram or photo. Any ideas? It's a 1979....

Thanks.

[o0sara0o]

Quick follow-up to post of a couple minutes ago:

I found the following diagram here on another thread: http://fiatspiderron.nl/weber-28-32-adha.html

ARE YOU KIDDING ME? It states at the bottom of the diagram that the fast idle diaphragm unit is "not used" on the 1979. Still present, just not used. Which would explain why there was a tiny screw in the vacuum inlet, and why the cam and linkage weren't hooked to anything...

If this is true, then what the heck--if anything--controls fast idle on my car? And could anyone suggest an explanation for why this fixer-upper suddenly decided to idle fast a few days ago? The idle adjustment itself works fine, and was not changed.

[o0sara0o]

Another follow up on fast idle adjustment in 1979 Spider, for the searchable archive if nothing else.

Got desperate, pulled the carb to figure out exactly what the mechanics are. Indeed, the fast idle diaphragm mechanism IS totally inactive on this carb, and it's that way from the factory apparently. Vestigial remains. Instead, the fast idle has been incorporated into the automatic choke, on the opposite side. It's a stepped lever contraption that is inserted between the idle adjustment screw and the throttle. Our problem is a return spring was missing in there, which was supposed to kick off the fast idle when things are running well and you goose the throttle. Will get a spring, see what happens.

The automatic choke is activated by coolant flowing through a water jacket, around a bimetallic spring that changes shape with temperature and moves a linkage. No clue about how to position the water jacket radially, which affects the action of the bimetallic spring.

Will post a solution if one found.

[So Cal Mark]

the fast idle diaphragm is an emission device, not the mechanism that creates a fast idle when the choke is on. They are too very different things. If you ditch that carb, you can pick up tons of performance with a 32/36 carb