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MG TD TF 1500 - OT-'72 MGB Won't Start

Hope you don't mind but I'm stumped. I’m posting this on both the T-series and the MGB Technical forums in hopes that someone will know the magic words. I’ve owned and enjoyed my ’72 mgb roadster since May. I drive it regularly and have put over 1,500 miles on it during those six months. Up until yesterday it’s always started and run great with two exceptions.
Last month, after a hundred mile rainy drive (wipers and lights all the way) the battery was dead and it wouldn’t restart. The next morning I roll-started it and it ran fine. After a few miles the battery was charged and it restarted fine. The next week, after sitting all day (warm and sunny) at the Euro Auto Festival, it again wouldn’t start. I borrowed a friend’s jump box and it started right up and, until yesterday, it continued to restart fine.
The weather has been rainy and cold for the past three weeks so I hadn’t started the car at all this month. Yesterday, cool and sunny, I decided to take it for a spin. After the first couple of seconds of cranking the battery faded and died. Due to the previous experiences I had acquired one of those lithium battery jump starters so I hooked that up and turned the key. The car cranked quite well and after a moment caught and I thought all was well – not to be. After running for just about 20 seconds I slid the choke back in and the car began to cough and sputter, spitting white smoke out the tail pipe before it just died.
The lithium starter pack has a thirty-second timer after which it turns off. I reset the timer and turned the key again. Same thing – it caught, I released the choke and after a few seconds it coughed, sputtered and died. I scratched my head, waited a while, drank a beer and tried again. This time and ever since, although it cranks fine, it never fires.
I looked at the points and they seem fine. I haven’t had a helper available so I haven’t pulled a plug wire to see it there is spark. There’s plenty of fuel in the tank and I can hear the fuel pump running when I turn the key. The car has been converted to a single 12v. battery and I’ve fully charged it with a trickle charger. The only other odd thing I noticed was that when it did catch and run for half a minute, the tach swung quite wildly.
HELP!! What would cause a car that was running great to just quit? What should I look for? What tests do you recommend? Thanks. Jud
J. K. Chapin

The tachometer swinging wildly indicates an primary ignition problem.Loose wires Pour points.
Sandy
Sandy

1) It does sound like you could use a new battery.

2) "White Smoke" not good. Could be head gasket. Do compression check.
3) the usual suspects.
Plugs
Points
Timing
Carbs


Jim B.
JA Benjamin

Thanks. I'll pull the points, clean them and check the gap and all the wire connections. Yup, I'm sure I need a new battery. Wonder if it's reasonable to get two small 12v. batteries and have a switch so one could back up the other. Also wonder if the lithium starter pack maybe did something to the points or ignition wires. Jud
J. K. Chapin

Again, Compression check first.

I doubt the difference between Lithium and lead acid is significant.

Jim B.
JA Benjamin

Jim, I suspect that you are right about the lithium battery jumper and also that I need a new battery. The one in it is an Extreme Magna Power 12v. that appears to be primarily for snowmobiles and skidoos. It has garnered several negative reviews on the web. Can anybody recommend a 12v. battery that will fit in the MGB battery box intended for a 6v battery? Thanks. Jud
J. K. Chapin

I've had a 12 volt battery in my B for 25 years. I prefer the gel type. No acid spills or the associated corrosion. My mind says a group 24...but I'm not sure.
MG LaVerne

MG, that sounds like what I'm looking for - hard white plastic case with a black top.. I guess it's off to O'Reilly's tomorrow with the old battery in hand to be tested and to ensure that the replacement fits. Jud
J. K. Chapin

Jud, The new battery will probably solve your problem and hopefully so, but on our 72, we had nearly the same problem and I had to send the alternator out and have the regulator replaced, which they replaced the original with a heavy duty one. That was in 2008. Just another idea. PJ
Paul161

IT RUNS!! The rest of the saga - Part one:
COINCIDENCE?? CAUSE AND EFFECT??
ONLY THE SHADOW KNOWS!
Well, the first thing I did was to post in inquiry on the MG forum describing the problem and asking for advice. The second thing I did was to ask some FBCCers (members of the Foot Hills British Car Club) for advice. Both resources came through for me.
Even though I knew I had fuel and the points, cap and rotor looked good, I did not know whether the problem was lack of fuel to the engine or lack of spark to ignite the fuel. Doug Hansen gave me a test to perform from the fuel side and one of the forum members gave me a test to perform from the ignition side.
Doug’s test couldn’t be simpler but it’s not something I would have just thought of. What he said was, “Squirt some starter fluid into the carbs and if it fires the problem is on the fuel side.” Doesn’t get any simpler than that so I gave it a try. The initial test was misleading because the engine fired up on the first try. “Aha!” I said, it’s a fuel problem. But no. After about half a minute the engine sputtered and died. Squirting more starter fluid down the carbs didn’t result in a restart. It cranked and cranked but no fire. Ergo, spark is the problem – or so it would seem.
The ignition side test was also fairly simple. Without a helper I couldn’t hold a spark plug against a head bolt while the helper cranked the engine. Turns out the test was something I could do myself. Instead of holding a spark plug and cranking the engine to open and close the points, just take off the distributor cap, hold the center hi-tension lead close to a head bolt and manually open the points with a screwdriver. The engine almost always stops with the points closed. With the ignition key on the coil immediately gets charged. If all is working properly, when you open the points the coil field will collapse and, Presto! You’ll get a spark to the block. Unfortunately, this test also proved to be misleading. Yes, I got the hoped for spark but the engine still wouldn’t keep running after initially starting and it wouldn’t restart unless I waited many hours.

So, what has this told me? When dead cold, the car starts and seems to run perfectly for 20-30 seconds. Then it dies. Then it won’t restart. I concluded that it must be something that fails after about 30 seconds and then, Lazarus-like, heals itself over night and works again for another 30 seconds. What could it be? I bet you can guess.
During all of this I discovered that the wire from the “-“ side of the coil to the distributor was badly frayed and hanging on by only one small strand (0.0085 inches) at the distributor terminal. Aha! Thought I – insufficient conductor that heats up and forms a high resistance block after just a few seconds. I replaced the wire and crossed my fingers. Varoom!! And I thought I was a genius and had fixed it. Thirty seconds later the engine died and I was back where I started. Drat!!
Continued ...
J. K. Chapin

The Saga - Part Two:
So, what has this told me? When dead cold, the car starts and seems to run perfectly for 20-30 seconds. Then it dies. Then it won’t restart. I concluded that it must be something that fails after about 30 seconds and then, Lazarus-like, heals itself over night and works again for another 30 seconds. What could it be? I bet you can guess.
During all of this I discovered that the wire from the “-“ side of the coil to the distributor was badly frayed and hanging on by only one small strand (0.0085 inches) at the distributor terminal. Aha! Thought I – insufficient conductor that heats up and forms a high resistance block after just a few seconds. I replaced the wire and crossed my fingers. Varoom!! And I thought I was a genius and had fixed it. Thirty seconds later the engine died and I was back where I started. Drat!!


Could it be something inside the distributor? I’ve heard lots of complaints about the lousy quality of the current crop of condensers so that seemed a likely candidate but how to test it to find out. By now it’s the day after Thanksgiving and the Bee hive in Clemson is closed so I’m not going to just drive over and get a new condenser.
But wait. I recently ordered two complete sets of points and condensers for the MG-TD so I do have two spare condensers. I have no idea if the condensers for the TD are the same as those for the MGB but they’re the ones I have so I give it a try.
I’ve always wondered why a part that’s prone to failure such as a condenser is located inside the distributor where it’s almost impossible to get to. I looked at some wiring diagrams and decided that electrically speaking “inside the distributor” and “hanging off the ‘-‘side of the coil” are the same thing. The wire from the points to the condenser is a bit longer but electrons go really fast and I hoped they wouldn’t notice the little extra time taken to get from the points to the condenser.
I popped off the distributor cap (for about the tenth time), disconnected and removed the condenser, screwed everything back together and put the cap back on. I unscrewed the nut on the “-“ side of the coil, attached the condenser flag there, put the nut back on and grounded the condenser to the frame (verifying with an ohmmeter that there was a good path to earth). Then I crossed my fingers and turned the key …
VAROOM!!! And not only that, the engine kept running and purred like a kitten. Forty to fifty miles later and it’s still running like a champ. I don’t know how long the TD condenser will last but hopefully at least until I can buy several MGB condensers to put in the ditty bag in the boot.

So, did the dying battery cause the condenser to fail? Did the almost broken wire create a high resistance point that prevented the coil from properly functioning? Did the failing condenser cause the battery to discharge and fail? Did none of these failures cause the other failures and it was all just an unfortunate set of coincidences? ONLY THE SHADOW KNOWS!
J. K. Chapin

This thread was discussed between 23/11/2015 and 27/11/2015

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