My Carb symptoms listed

[stuartrubin]

All, I have made lots of posts about my carburetor and I appreciate everyone's thoughts on the matter. I just can't get thing thing right, so if you would please indulge me, here is a list of "symptoms". Maybe seeing them all at once might tip off some smart folks as to what's wrong. All advice is welcome!

Some background: the PO gave me the car with the automatic choke no connected. The mechanic (who I don't think really knew what he was doing) has "played" with it some, to no avail.

• Carb is a 34 ADF (not original to the model year) and apparently not 100% standard since the mixture screw is non existent. (See http://fiatspider.com/f15/viewtopic.php?f=5&t=30934)
• Always idles high. No matter what I do, I cannot get it below 1500 RPM.
• When running, throttle doesn't seem to close all the way. Drifts back slowly then needs to be "nudged". Still idles high.
• After the last time the mechanic "adjusted" it, the water choke was installed at about a 45-degree angle. Aligning the marks seems to have no affect.
• The fast idle adjustment doesn't seem to do anything. It was screwed in completely, but pulling it out seems to have no affect. I don't know if the "button" for adjusting the fast idle is even doing anything.
• The idle solenoid USED to work, but now, if I disconnect the wire, nothing changes. I can hear the "click." (Previously, I had problems with the engine dying when I let up the gas; replacing the solenoid fixed that.)
• Rough or unsteady idle (but not terrible)

Thanks, people!

[johnsje6]

For what it's worth - I bought a Chinese 34 ADF for my '79, and the idle just kept going up no matter what I did with the idle stop screw or mixture. Turned out there is also a stop screw for the secondary butterfly that was loose and kept vibrating looser which was holding the secondary open, which kept the idle high. Not sure if that is your problem but worth a look, will probably have to take the carb off to get to it.
Here is the thread with photos - good luck!
http://www.fiatspider.com/f15/viewtopic ... 1&start=30

[mattyd7]

Not for nothing, but looks like you've been messing with this for a few months and you seem to have multiple issues with the carb, between backfiring, high idle, mix screw, regular idle, choke, throttle plates, etc. I hate to say give up, but maybe this is a good time to replace the carb and start fresh. If you don't know when it was last rebuilt, it probably could use that anyways and for the time and hassle you've put into this...yeesh. I've seen at least one used ADF up on the for sale section for really cheap a few months ago, probably some others in the same time.

Maybe it's one thing that needs to be fixed like the previous poster pointed out with the loose screw, but really it seems like there is a lot wrong with this carb. If his recommendation doesn't work, I'd start looking for a known good used carb or a new one!

[gchocevar]

I've been there with an ADF on my 79 also. Ran high idle right after the engine/cab rebuild. I could force it down and it idled perfectly, but as soon as I stepped on the gas justa little, it would idle at 2500 rpm hot.

I was about to give up when I tried an old trick of silicon spray around all moving parts outside of the carb. It worked. Every spring I give it another shot. I am sure its due to loose tolerances and binding of old carb linkages. It beats buying a new one.

Good luck,
Greg

[stuartrubin]

Matt, unfortunately I've already sunk more money into this car than I had expected, so I'm trying to avoid just buying a new / refurb carb. If I knew what the problem(s) was (were) I could make that rational decision.

There are a few things I have not done, like take off the choke make sure that it's setup right internally.

I'm also curious about the electrics (if any) on the fast idle.

Greg, I have sprayed the crap out of everything that moves, but it's no help.

Thanks for everyone's help, and I'm still open to suggestions!

[bradartigue]

If the car continues to run with the solenoid disconnected, and the solenoid works, then the carb is delivering fuel from somewhere other than the idle circuit. Most likely the throttle speed stop screw is set with the throttle open at rest. It may also be the choke (which has a device that partially opens the throttle) is set entirely wrong.

I would back out (not remove) the throttle stop screw so that it does not engage the throttle mechanism at all, then see if the thing idles off the mixture screw alone (it should idle low and poorly). Then true it up by the throttle stop screw. If with the screw slack it still idles high then I would remove the water choke and completely slack off the spring and inspect where it connects to the throttle, potentially adjusting.

Most importantly is to check for air leaks, open orifices etc.


I will say that your carb is not one I think designed for a spider and you'll have issues. With the mix screw on the other side I'm not sure how your throttle adjustment even works, leads me to believe your primary barrel is on the wrong side.

[stuartrubin]

Brad, great advice as always. In fact, over the weekend I did a lot of what you suggested - completely disengaged the idle stop screw, disconnected the choke, ran without the choke, reset the choke...

I think the take home message here is:

I will say that your carb is not one I think designed for a spider and you'll have issues.

I started looking into buying a new Chinese 34 ADF to replace my Frankenstein carb. From reading this forum, it seems that they are a good value, if not without their quirks (shipping damage, loose screws, unmarked jets, etc.) that can be mitigated.

That aside, I did have one more clue which may or may not be related. After getting things "setup", I took the car for a spin and the brakes were working like crap. These was also a "hissing" sound I've never heard. I don't know much about brakes, but I think the booster may have become disconnected or has a bad leak. Wouldn't a disconnect to the booster cause a serious vacuum leak and cause some carb problems?

Thanks, Professor Brad!

[bradartigue]

Well now hold on there...hissing is usually a bad booster diaphragm. A bad booster diaphragm is a big old air leak, right into the manifold, which causes high idle speeds.

Fix one thing at a time...the brakes will work without the booster (though they feel a bit hard). Disconnect the booster at the intake manifold and cap the hole. Now try to set the carb idle.

If this doesn't do it then yeah, replace the carb. I have one here, a Chinese one, unused, if you're interested. I bought it for a car we never installed it on and it has sat on a shelf ever since.

[stuartrubin]

Brad, thanks for indulging me on this. I'm really not THAT lame, but I'm new! To add to the confusion, I futz around with things today and the hiss went away. It MAY have been that the other day I was driving with the air filter off and I was just hearing the normal sucking of the carb. (Yes, my carb sucks. Pun intended.) But, tonight, it was quiet, but the brakes were really hard to work.

So, I get the theory, but I'm not actually 100% sure what parts are what. Specifically, the "Workshop Manual" talks about the "brake servo", but no mention of a "brake booster." Are these the same thing? If I google "brake booster", I get images that look like this:


Is this the same part (only shinier!) as mine here shown as "A"? It looks a lot smaller in the ad. I don't quite see how that could be since there is no obvious connection to the mater cylinder.

There is a vacuum line (I assume) connecting "A" at point "B" to the intake manifold at "C". I think you are suggesting that I cap off "C" and see if that bring the idle under control. If it does, than the problem MAY be the booster or the line to it. If it's still bad, than the carb is bad, and no explanation for the bad brakes; it's a separate problem.

What's the best way to cap this? Pull off the tube and put a rubber cap over it (if there is something that big? I'd hate to suck something into the engine!) Unscrew the fitting over the nipple? Any idea what size screw-on cap that needs?

Here are the pics. Again, thanks to you and everyone else of the help.

[Rambo]

Actually dealing with a bad booster right now. I noticed 4 days before it blew out that when i hit the brakes i had a hissing noise inside the car. Also when the motor was cold it gave it a fast idle and when it was hot it dropped it and even stalled it once. Then i was driving it and my power braking went out still with the hissing. I pulled the line it was good so im going to have to replace the booster. Hope this will help.

[131]

Is this the same part (only shinier!) as mine here shown as "A"?

Yes, brake booster or servo. It has a large diameter diaphragm inside, one side is open to atmospheric pressure, the other side vacuum from the manifold. The large surface area and pressure differential assist brake effort, less pressure is needed on the pedal.

There is a vacuum line (I assume) connecting "A" at point "B" to the intake manifold at "C".

Yep, a leaky connector, hose or stuffed diaphragm causes vacuum leaks and idle/carb issues.

I think you are suggesting that I cap off "C" and see if that bring the idle under control.

If you have a leak between "C" and the booster, capping it off will help in diagnosing issues. You'll have no vacuum assist on the brakes and the pedal will require extra force to get any brake operation.

[stuartrubin]

So, I capped off the vacuum supply to the brake booster at the intake manifold. There was no change in the carburetor performance - still super high idle, "stickiness", etc. So, I think I have a bad carb AND a bad brake booster (or maybe just the hose of valve...)

This may be a red herring, but I noticed one more thing. The choke cam does not look quite like the one in the "Workshop Manual." The difference are subtle, and may not matter, but there are 6 stops (not 4). The spring arrangement may also be different. One reason that I point this out is that this may be another clue that this carb just does NOT belong on this car. See below.

Brad, I'll PM you about the Chinese carb.

Thanks