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General Tech Stalling, Chugging, Engine Shuts Down

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KVH

KVH

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I rebuilt my carbs two weeks ago and proudly announced how perfectly my engine was running. That truly was the case, but now I’m back to the same problems with this car, TR4A. Yesterday, after a nice drive, I restarted the engine to head home, and it started right up. But, suddenly, the rpms slowed, the engine chugged and shut right down on me. The car backfired, and smoke puffed from the exhaust pipes. My friend said the puff was grayish brown.

I pulled the plugs and they were a bit black, from a slightly rich mixture. I leaned up the carbs two flats, put in brand new spark plugs, and the car started right up smooth as ever, but only for 25 seconds. It chugged and shut right back down.

My coil was very hot if that’s any clue. Not sure why it would be so hot since the car was hardly running. Current to the coil is good, and the connections are solid. My fuel pump is fairly new, maybe one year old. I had just filled the gas tank the evening before.

I’m at such a loss, having checked so many things. It seems I ought to start random steps: Like a new distributor cap; new rotor; maybe blow compressed air back in the fuel line to the tank to see if there’s a clog; check my generator connections and my battery post connections.

But first, as usual, I’d value the input from this forum. Any thoughts appreciated.
 
Backfire through the exhaust is ignition. It's not your carbs this time!

I would start with a check of the lead into the distributor, to ensure it is not grounding. Then double check the rotor and cap contacts on both sides. The hot coil after only a few minutes is not normal. Check the instructions, as some coils require a resistor in the 12v lead going to it.
 
I always hate to recommend throwing things at problems. But in this case I would likely replace the coil and condensor.
Charley
 
I just checked and recheck everything. I even replaced the distributor cap. The car started right up and, once again, ran for about 25 seconds and then quit. I’m gonna now try replacing the coil. The one I have gets awfully hot.
 
+1. There has been a rash of bad condensers. If you recently replaced it, you may have gotten a bad one. A shorted condenser can also explain a hot coil.
 
Would a bad condenser just suddenly make a car start choking, missing, sputtering and then quit? It really was quite an extreme occurrence.
 
I have had both condensor and coil fail. Coil was pop pop and then die. But start again until it just wouldn't start. Condensor was a couple of dead moments and then within a couple minutes dead with no hope of starting.
Charley
 
Warning...science to follow!?!

The purpose of the condenser is to prevent the current from jumping the gap and sparking as the points open, which burns the point faces. When the points are closed, the current into the coil generates a magnetic field. Once the points open, the magnetic field collapses, which causes the high tension spark...but the collapsing magnetic field also tries to back feed thru the points with a spike of a hundred volts or more. The condenser gives this reverse voltage a place to go, rather than back across the tiny point gap as a spark. If the condenser goes bad as an open circuit, then the points burn in short order, so they cannot pass the required amperage to the coil. If the condenser shorts internally, then the coil will be loaded continuously, so it will be constantly under load. Failures are rarely perfect, so there are variations in the way the car acts. For example, the condenser may start to absorb the reverse voltage spike, but reach a point where it then shorts...or opens... as the spike gets too high.

In summary, try a different condenser, and look closely at the points to see if the faces are rough and pitted. File or replace the points if they are pitted. If none of this works, then try a different coil. These steps should get you back on the road again!
 
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I now have the car running great after a few guess fixes. New points, condenser and coil. But I’m not trusting it. What happened left me stranded roadside. I’m still looking at other things.

Questions: Must timing be reset every time the points are readjusted? My timing was way off after I installed the new points. Probably off by 6 or 7 degrees more BTDC. Total 10 or 11. I was also surprised my balanced carbs had to be rebalanced.

Also, is it normal for the coil to be extremely hot while the car is sitting with the engine off but the ignition key turned on?
CJD said:
Warning...science to follow!?!

The purpose of the condenser is to prevent the current from jumping the gap and sparking as the points open, which burns the point faces. When the points are closed, the current into the coil generates a magnetic field. Once the points open, the magnetic field collapses, which causes the high tension spark...but the collapsing magnetic field also tries to back feed thru the points with a spike of a hundred volts or more. The condenser gives this reverse voltage a place to go, rather than back across the tiny point gap as a spark. If the condenser goes bad as an open circuit, then the points burn in short order, so they cannot pass the required amperage to the coil. If the condenser shorts internally, then the coil will be loaded continuously, so it will be constantly under load. Failures are rarely perfect, so there are variations in the way the car acts. For example, the condenser may start to absorb the reverse voltage spike, but reach a point where it then shorts...or opens... as the spike gets too high.

In summary, try a different condenser, and look closely at the points to see if the faces are rough and pitted. File or replace the points if they are pitted. If none of this works, then try a different coil. These steps should get you back on the road again!
Click to expand...
Fascinating stuff. Thanks for that. If I’m understanding, the opening of the points collapses the magnetic field causing the spark to shoot up thru the distributor cap to the plug wire corresponding to the rotor position. The condenser somehow controls the spark so the coil is not under constant load.

Does this mean that with the engine off but the ignition key on, and the points closed, the coil would be under constant load and get rather hot after several minutes of that condition?

When my car stalled and wouldn’t start, I noticed that my coil was extremely hot, definitely too hot to touch or handle. Does that say anything in particular? To me, based on the above, it says that the condenser may have gone bad, or my coil may have gone bad,

My points, incidentally, were only slightly blackened, and had no pitting. I could easily file and make new. One note: I am using a Race Distributor, and it does have that little funky spring loaded clip to hold the condenser and coil wire. I don’t particularly like that set up, as the wires, in my view, are a little too close to ground. See pic.

Anyway, among the best parts of all this for me, is just learning.
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Part of your answer.
I had a friend with a Austin Healey who left the key on for maybe an hour ( by mistake). It burned up the wire from the coil located on the back of the distributor. Coil was hot as well. We had to locate a substitute replacement part to get him going.
When eat of the coil and condensor died ( as did the car) I only replaced the single part. And back on the road!!
Charley
 
To answer your question: if you do anything to the points you must recheck the timing. In theory, if you got the points gap exactly as it was before working on them, you wouldn't have to recheck the timing. But that never happens.
 
Also, if you have a very hot coil (let's say, too hot to leave your had on it more than a few seconds) something is very wrong. Either the coil has failed or you have a coil with too-low primary resistance. I also don't like the practice of throwing parts at a problem, but there is no reliable way to test a coil. You have to substitute a known-good one.
 
I just swapped out two more coils on my TR4A. I have several new and used. Every coil on this car gets too hot to touch. Voltage to the coil is about 11.59.

I’m using Moss Cobalt brand plug wires. My plugs are new. Gapped .025.
 
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A little follow-up: Because I recently stalled and couldn't restart after 30 minutes of trying, and because I've chased down every issue from my fuel pump to ignition, points, condenser, and coil, and because my car is now running great--at least for now--I need to run something by you folks who know more than me.

Here it is. Two nights before I got stuck stalled at the roadside, I had rebuilt my carburetors. I did it correctly, except for the floats. For the floats, I used the little manual photo illustration of leaving 1/8 of an inch gap between the float chamber lid and the black plastic float. I felt I perfectly replicated the recommended gap.

However, last night I noticed that the fuel in the jets was, at idle, literally spilling out of both jets, over the jet bridge and into the intake manifold. I removed the floats and adjusted them slightly, and still I had the same problem. I removed the float lids at least four times, readjusting the floats by bending the little lever bar upward. By the time each fuel level seemed proper, right below the top of the jet, that 1/8 inch gap became more like 1/4 inch, maybe even 5/16.

But the fuel level appears correct, and the car starts and runs great. But it also did before a got stuck the other day.

So, here's my question: If the floats were allowing fuel to spill over the bridge into the intake manifold, and essentially flood the engine, would the symptoms be what I experienced--start up after the car had been hot, then sitting idle for 45 minutes, followed by immediate chugging, loss of power, and total shut-off and stall? That's what happened to me.

And, BTW, my fuel pump seems fine. Right about 2.2 lbs. And putting in new plugs did virtually nothing on the side of the road. The car started right up with the new plugs (maybe 90 minutes after the initial stall and shutoff) but then shut right back off, chug, chug, hiccup.

If my problem was not the float adjustments, then whether my new points, condenser and coil make a difference will be just guesswork for now.

Thx
 
What you did with the floats is perfect. The level at the jets is the goal, so it doesn't matter what you measured on the float arm.

In answer to your other question...leaving the ignition on with the engine off is always a HUGE no-no on a point car! This has obviously been forgotten since cars have been electronic for almost 50 years now. The problem is exactly what you pointed out (no pun intended!)...if the engine stopped with the points open, then the coil is not energized and all is good. But, if the engine stopped with the points closed, then you are providing constant power to the coil. You will burn out the points AND coil in short order!! You never know where the engine stopped, so leaving the key on more than a minute with the engine stopped is rolling the dice. If you do it regularly you will damage the coil and points.

As for the chug chug. Here are some rock solid diagnostics to point you in the right direction.

1) Backfire out of the tail pipe is always, as in ALWAYS an ignition failure. That does not mean you cannot have another problem with the ignition failure, but you have an undeniable ignition problem if you ever get back fires out of the exhaust. If not fixed, it will quickly blow your muffler out of shape. Things to check...points, condenser, coil, primary and high tension wires, rotor, cap, plugs for fouling.

2) Back firing out of the carbs is ALWAYS very lean fuel supply. Cam timing can also cause it, but I will assume you know that the engine was put together properly. If you don't know, do a compression check, as cam timing will lower your compression. But, for an otherwise good engine, carb popping means your mixture is extremely lean. If it happens when you gun the throttles, then first check the dashpots for sufficient oil. Dashpots give a lean mixture on acceleration.

3) Mildly lean engines will surge up and down every few seconds while idling. It will rev up a few hundred RPM, and then back down a few hundred RPM. Any lean condition can be either a float issue, a mixture nut issue, or a vacuum leak issue.

4) An engine that idles good, but slowly gets rougher...and rougher...until it stalls, is a sign of a high float (like your dribbling down the intake condition you fixed), a rich mixture nut setting, or a fuel pump over-powering the float valve.

5) Any engine that runs rough and puffs black smoke is rich.


These above written rules are gospel. They will immediately point you to the area to look into if you have idle problems.

Oh...a little comment on coils. Coils can fail completely, which brings you to a halt and you will not go anywhere after it fails. Most commonly, though, the high tension insulator starts to break down. The coil will then work well when cold, but will cause dying and/or backfiring out the exhaust once it gets hot. So it can run well cold, but act up when hot.

Hope this helps!
 
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Yes; thx. Hard to trust what to expect next. Maybe I was totally flooded. That could make sense, unless it really was the coil. If the coil, it was fairly new and highlights the necessity to carry spares.

Thanks again for all the input. It’s committed to memory.
 
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sp53 said:
If you have S.U. carbs, I would think the needles in one the floats are sticking.
Click to expand...
I also just replaced the float needles. The float bowls were very clean, but I did find one spec of fuel line rubber that I suppose could have been an issue.

In replacing the float needles, I used two non-viton (not the rubber tipped) ones I had as spares. Not sure that was so wise, since I don't even see where the ones I used are offered anymore. Everything new I'm seeing is viton tipped.

Well, anyway, I'll see how it all goes. I'm still reluctant to accept that my complete engine shut-off and stall would be from flooding. It seems a few minutes of waiting and retrying with the ignition would have done the trick. But not here. It seemed like I totally lost power, maybe spark, so, again, maybe the coil, which is disturbing since it was probably less than one year old.

But it's all fun, and I'm running great now, so no complaining here!
 
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