Rough running then stall.

[alfapop]

1972 Spider. Car was running great this summer and then suddenly it started running rough, with the engine surging and hesitating, and then it stalls completely. I've had two professional mechanics look at the car and neither figured it out. Ignition is all relatively new, plugs are getting spark, new plugs, fuel pump has good pressure and the carburetor is getting gas. Carb was rebuilt about a year ago. A week or so ago it ran pretty well for 2 miles and then while just cruising straight and flat it just stopped. Now I can't get it to run for more than 60 seconds. Any ideas?

[bobplyler]

Are the fuel lines OK? In engine compartment and trunk?

[18Fiatsandcounting]

And a few more questions:

1) How well does it idle?
2) If it idles, and you have it sitting in the garage/driveway and slowly increase the rpms by opening the throttle by hand, does it start to falter at some point?
3) How do the plugs look now? Black and sooty, or ??

It sounds fuel related to me, and it's important to find out whether the engine is getting too much fuel or too little. Standard diagnostics should be able to tell the difference.

-Bryan

[alfapop]

The fuel lines look fine. When I last tried, the car started right up strong and idled for about 10 seconds. Then a hesitation, kind of like a miss. Then the hesitations increased, it starts balking with the tach jumping up and down, and then zero. I can't get out of the car and manipulate the throttle by hand as the car would stall before I got there. One thing that may be a key is that I put in new plugs, thinking maybe that was the problem, and after running it for a total of maybe 10 minutes (I did get 2 miles down the road once before it just died while running on a straight, flat section of road), I pulled one of the plugs and it was jet black, covered in soot. I have a video of the car starting and stalling but can't figure out how to insert it to this post. I expect that isn't allowed for cyber-security purposes. So why is the plug black? Incomplete combustion? Oil in the cylinder? What to do next?

[Nut124]

What kind of a distributor does it have? If the old points type, I'd consider upgrading to the later electronic dizzy.

Tach needle jumping points to an ignition problem to me.

[18Fiatsandcounting]

....I pulled one of the plugs and it was jet black, covered in soot. I have a video of the car starting and stalling but can't figure out how to insert it to this post. I expect that isn't allowed for cyber-security purposes. So why is the plug black? Incomplete combustion? Oil in the cylinder? What to do next?

Black plugs are incomplete combustion. The usual cause is an overly rich mixture, so not all the fuel is burnt leaving carbon residue on the plugs (the ideal outcome is all carbon dioxide which is a gas that goes out the exhaust).

Another cause can be an ignition system that is weak, in other words the spark just barely ignites the air/fuel mixture.

Since your tach is bouncing up and down, I'm leaning towards an ignition problem. A '72 spider has points, so those should be in good shape and set correctly. Incorrect point gap (dwell) can cause issues with running, including tach problems.

Dwell should be 60 degrees. Later model years had 55 degrees of dwell, and the exact value is tied to the rpm range of the engine (it's complicated).

So, in answer to your question of "What do I do next?", my answer would be check the ignition point dwell.

-Bryan

[alfapop]

Thanks. I will try those things. BTW - You last name doesn't start with "SH" by any chance does it? Formerly of Boxborough, Mass?

[18Fiatsandcounting]

Nope, sorry, my last name is Balazs. Kind of has a "sh" sound at the end, but it doesn't start with Sh. I don't recall ever being to Boxborough MA either.

-Bryan