Will not idle!

[PaulC]

Just finished up the single plane and carburetor ( rebuilt ADFA) swap on my 79 Spider.
After a bit of cranking to get the new fuel pump and lines full, it started right up.
Only problem is that it won't idle. Runs around 2800 rpm and neither the idle speed screw nor the mixture screw.seems to have any effect.
Haven't checked the timing yet since it won't idle low enough to be accurate (I'm thinking).
Any thoughts and suggestions would be appreciated.

[18Fiatsandcounting]

Sounds like you might have an air leak into the intake manifold. Air leaks will cause the idle to run quite high, although 2800 rpm is higher than I've seen (usually it's 1500 to 2000). Anyway, check all the vacuum lines to the intake manifold and plug them off one by one to see if you can figure out if that's what the problem is.

-Bryan

[PaulC]

Will give that a try and report back.

[PaulC]

Spraying starting fluid around the base of the carb does increase the engine speed so perhaps it's a gasket issue. All vacuum lines (All 3) look ok.
Was able to get the speed down to around 2200-2400 rpm be backing off the choke idle screw, possible misjudgment there. And the choke is not engaged as it's near 100 degrees here.
Now when I turn in the mixture screw in it brings the idle down but only when it's nearly seated but not nearly enough.
Have to pull the carb off and check the base gaskets

[GeorgeT]

When you look down the throat of the carb are the butterfly valves closed? If not check the throttle linkage, it needs to have a very slight amount of slack in it.

[18Fiatsandcounting]

Spraying starting fluid around the base of the carb does increase the engine speed so perhaps it's a gasket issue. All vacuum lines (All 3) look ok.

Sounds like you may be on to something. When you have an air leak, it's just as if you were opening the throttle and letting more air in, so the speed goes up. Their isn't any fuel along with that air leak, but this doesn't matter as the regular idle circuit provides the fuel and the car can run very lean at idle and still keep running. It won't have much power under this lean condition, but you can't tell since you're not driving it, and all it needs is a few HP to keep the engine spinning.

When you pull the carb to check the gasket, put a straight edge across the bottom of the carb and the manifold flange to make sure they're flat. They don't have to be perfect, but you don't want any warpage. Also move the throttle shafts around by hand and see if they feel loose in the side-to-side direction. If the throttle shaft is worn, that's another possible source of air leak.

The tip of the choke idle screw should be fully disengaged from the cam it rests on (when the choke is off), so check that if you can see it. And as George mentioned above, make sure the throttle is allowed to completely close. No binding of the linkages and cables, interior carpeting holding the throttle open, etc.

-Bryan

[PaulC]

Thanks folks. All things to check.
The butterflies appear to be closed, but I'll check for the slack in the linkage.
Shouldn't be much leakage around the shafts as I rebuilt the carb and replace all the bushings that were replaceable.
As a parallel effort, I'm also getting air out of the cooling system as the engine now overheats but didn't before the swap. I had to drain down the coolant to remove the intake manifold so now I'm in the fill-run-refill cycle with the flush tee.

[manoa matt]

There are a few on the bench checks and adjustments with regards to setting the automatic choke, the fast idle cam, choke unloader, choke plate min and max opening, and the secondary throttle plate gap. All of which are not covered in the factory manual, but are covered in the 32ADFA carb workbook which is a supplement to the factory manual. The workbook can be found at this link: http://www.njfiats.org/joomla/images/st ... rkbook.pdf

Send me an email and I can send you a few other files for that carb. matt.scarton@gmail.com

[PaulC]

Thanks Matt, that's just the.book i used to set up the carb after overhaul.
I also have all manner of other info on the Weber carbs, some in Italian with and without translations.

[PaulC]

Success!
All It took was a new spacer and gaskets .
Idles great now and the mixture screw actually has the desired effect.
However now it pops thru the carb after revving.
Mixture may be a.bit lean yet. I need to check the timing and fiddle the mixture and idle speed.a.bit .
All in all I'm happy with the conversion so far, but yet to actually drive the car.

Also, the overheating appears to be settled too after several more filling and burping cycles.

[18Fiatsandcounting]

However now it pops thru the carb after revving.

Awesome work on tracking down the air leak and the overheating issue. Regarding popping back through the carb, there are several possible causes: incorrect mixture (possibly), ignition timing is off (also possible), or cam timing is off (unlikely at this point). The origin of the popping is usually that some of the gas is still burning when the intake valves open, and so it pops back through the carb. Faulty emission control items can also cause this, now that I think of it.

You can do a quick check on whether it's running too lean by putting a piece of wood or metal over the top of the carburetor to partially block the inlet, which slightly richens the mixture. Kind of a poor man's choke. If you can get your fingers in there to partially close the choke, that works too. Try revving it and see if things improve or get worse. I normally use my hand for this, but given the popping back through the carb, that's not a good idea in this case... Anyways, if things improve, then your mixture is indeed too lean.

-Bryan

[PaulC]

Thanks Bryan for the suggestion.
I'll give that a try today and see what happens.

[PaulC]

Check timing. Simple job ... NOT!!
Made the rookie mistake of grabbing the #1 plug wire too far up the cable and not catching the plug connector . You guessed it, pulled the fracking cable right off the connector
Now have to order a new set as the cables don't come individually. Oh well, need to clean the plugs in the meantime.

[JohnHSpider]

I appreciate your help. I had the same issue, followed the steps presented and was able to solve it! Mine had a vacuum line issue.

[18Fiatsandcounting]

Made the rookie mistake of grabbing the #1 plug wire too far up the cable and not catching the plug connector . You guessed it, pulled the fracking cable right off the connector

Well, if it helps any, I just did this the other day with a brand new (straight out of the box) plug wire... I thought I had grabbed the connector, but apparently not.

You might be able to pry open the connector on the end and cut off some cable and recrimp it, but I've only been marginally successful at this. Requires a special crimping tool, and stripping back the rubber insulation on the wire without damaging the inner carbon fiber core is very tricky. Anyway, sounds like your plan is to just get a new one.

-Bryan