Crazy from the heat?

[stuartrubin]

Short version: I parked at the grocery store for about 20 minutes during a very hot (for Cleveland) day, about 90F, top down. The car would not start, but after about 20 minutes of waiting (top closed), it started right up. What could cause this? The heat?

Long version: I replaced the ignition switch earlier this year. I also re-jetted the 34ADF carb, but have not properly adjusted it. I've only taken the car out a few times, but have not had any trouble. After sitting out in the heat, the car turned over strong, sounded fine, etc., but just would not start when I released the key. (These were the same symptoms of my bad ignition switch, which may be a red herring piece of evidence. In fact, the heat may very well be a red herring as well...)

So, what could cause this?
Vapor lock? (Not even 100% sure what that is...)
Mechanical deformation of connector(s) causing a bad connection, i.e. around the ignition switch?
Is there some kind of overheat sensor?
Same as this "Overheating / Air Bubbles"http://www.hwww.fiatspider.com/f15/view ... 5&t=39927??

Thanks!

[18Fiatsandcounting]

The issue could be related to the ignition switch, but since the engine turns over normally but just won't fire, I'm thinking it's something else.

Even if you have vapor lock (the gas is turning to vapor in the fuel lines), you would still have enough gas in the carb float bowl to start the engine and run it for 5-10 seconds or so. And, vapor lock at sea level at 90 oF would be unusual.

How is your ignition system? Plugs, plug wires, points/condenser, coil? If any of these are really old, that could cause issues with hot starting. Do you still have the original dual point ignition setup? That could be causing issues as well.

Another remote possibility is that the engine got flooded. If it happens again, try cranking while holding the gas pedal to the floor. Don't pump it; just hold it there. This helps clear out the excess gas in the engine, and then it often fires right up after a bit of cranking. I've seen this on older carbureted American cars, although I have to admit that I haven't seen it on a Fiat.

-Bryan

[stuartrubin]

Bryan, thanks for your thoughts.

The issue could be related to the ignition switch, but since the engine turns over normally but just won't fire, I'm thinking it's something else.

I'll clarify a little bit. I think it could be related to the wiring to/from the ignition switch, not the switch itself. It's currently somewhat of a bird's nest, and I being colorblind, I really hate messing with the wiring. But, all the connectors seemed tight, I did some "jiggling", etc., and that did not seem to help.

Another piece of data is that I don't remember hearing the fuel pump. I usually notice it kick in and hum as soon as I turn the key to the running position. I'm going to have to listen again and take a mental note when things are working normally. Could the fuel pump stop for some reason (and I mean stop, not just run but not push fuel) when hot?

Even if you have vapor lock (the gas is turning to vapor in the fuel lines), you would still have enough gas in the carb float bowl to start the engine and run it for 5-10 seconds or so. And, vapor lock at sea level at 90 oF would be unusual.

True! I didn't even get a second of running.

Another remote possibility is that the engine got flooded. If it happens again, try cranking while holding the gas pedal to the floor.

I have a high school memory of my friend's dad yelling at him with his old Triumph Spitfire, "you're gonna flood it!" And someone else telling him the trick that you can try starting holding the accelerator down. I did try this, but I suppose it's a remote possibility.

Who the hell knows. We're going to have another hot day today. Maybe I'll drive around the neighborhood and see what happens.

Thanks!

Stuart

[18Fiatsandcounting]

Let us know what happens.

Going from memory here, but I believe the fuel pump and ignition circuit are the same overall circuit on a '75, which would point to something besides the ignition switch. However, the wires to each are different of course, so it is possible that there is a flaky connection for the fuel pump that goes out when it gets hot. However, you would think it would do this when you're driving, and not just sitting after 10s of minutes.

Also, you float bowl would still have fuel in it, even if the fuel pump didn't turn back on after 20 minutes, and so it should at least fire and run for a few seconds until it empties the float bowl.

I'm still thinking something in the ignition when it gets hot, but drive it around and see what happens and try to remember as many details as you can.

Another thought that just popped into my head: I recall that the start electrical circuit and the running circuit for the fuel pump are different, and the running circuit depends on at least some oil pressure to activate it (a safety feature to shut off the fuel delivery in case of an accident). However, the start circuit bypasses this since you don't have oil pressure when the engine isn't started yet. It's possible that the start circuit to your fuel pump is flaking out when it gets hot.

-Bryan

[bobplyler]

I had a similar problem years ago.

One of the hoses had a pinhole leak. It only leaked when the engine was real hot. It sprayed a tiny stream of water onto the coil. After sitting, the water would evaporate, and the pinhole would close.

[stuartrubin]

Folks, it's been a while since this post started. Unfortunately, due to a lot of reasons, I just hadn't been driving the FIAT too much, but I have gone out for the last few days and it's been hot. My hunch is that it's not related to the ignition switch. Here are some refined set of symptoms.

Regardless of the temperature, how long it's been sitting, etc., the car takes several cranks, and some gas pumping to get started.

When it's warmed up, or even maybe when it's just very hot outside, the car frequently stalls when idling. This includes coasting to stops.

After the warm-up cycle (i.e. not when the choke is engaged) idle sounds a little rough (but honestly, I've never actually experienced a smooth idle at the correct speed, so I can't be sure it's wrong.)

So, what are we thinking here? All thoughts are welcome!

Thank you!

[18Fiatsandcounting]

So, what are we thinking here?

I'm thinking more than one thing is going on, but let's start with the idle (or lack thereof). If you haven't rebuilt the carb, it might just need a good cleaning and new seals/o-rings. The idle mixture jets might be partially clogged, or the idle mixture screw is set way off from where it should be.

Try this: With the engine off, note the position of the idle mixture screw and screw it in gently until it starts to seat. Don't force it. If it takes less than 1 or more than 2 turns to seat the screw, the idle isn't set up right. Make sure you screw in the idle mixture screw at the base of the carb and not the idle speed screw or idle jet holder. When you're done, put the screw back where it was.

By the way, which carb do you have? 32ADFA?

-Bryan

[stuartrubin]

Bryan, I will make sure the setup is reasonable like you suggested.

The carb is actually a fairly new Chinese knock-off Weber 34ADF.

Also:

Make sure you screw in the idle mixture screw at the base of the carb and not the idle speed screw or idle jet holder.

are wise words! All those screws look the same! Don't ask me how I know...

Thanks

[18Fiatsandcounting]

Very good Stuart, carry on! On the Chinese knockoff carb, carefully inspect the carb passageways as much as you can. Some carbs are pretty good, but some have been known to have bits of metal flashing stuck somewhere or casting imperfections which interfered with the fuel or air flow. Use strong flashlights and lots of carb cleaner.

-Bryan

[TheBender]

I had some similar symptoms when I first bought my car. Hot days it would stall and would need to let it sit for 20+ minutes before I could get it started again. Thinking back I believe it seemed to be related to the fuel return line not being connected. I ended up having a stock 78 carb rebuilt and it’s been running great ever since.