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MG TD TF 1500 - scraching my head

Not really a T series question but close. My friends "A" has a '62 "B" engine in it. It is really running rough and backfiring.
I adjusted the valves.
Confirmed the firing order 1-3-4-2
Checked the resistance of the plugs
Cleaned and gapped the plugs
Inspected the distributor cap and polished up the rotor
Did a compression check. #1 was a little low. 120 compared to 145 on the other 3.
It has Pertonics ignition.

Any ideas what I might try next?
Bob McLeod TD 5618

I didn't see anything about checking the timing. Did the happen suddenly or over time?

Alex Waugh

Timing chain could have jumped a tooth if its worn.
Spark coil could be bad.

Jim B.
JA Benjamin

Take the petronics out, and replace it with points!



Start the car in complete darkness and watch for sparks jumping between the plug wires,,,,


is it in through the carb throat or afterfiring as in out the tailpipe?
do you have a vacuum gauge?
regards, tom
tm peterson

Mixture too rich?
D. Sander

The backfiring is in the exhaust system. The problem started immediately after starting the car. It had not been previously run for about two weeks.
Bob McLeod TD 5618

I don't really like to fit pertronix units because when they go bad, they do so without warning. The "bad" part can manifest itself in any number of ways - not starting at all, spitting and popping, high-speed miss, low-speed miss, etc.

So I also recommend replacing the Pertronix with the points plate (many Pertronix owners carry a spare in the toolbox), and see if that fixes things.

You have to start somewhere...

Tom Lange
MGT Repair
t lange

My bet it's timing, with one or more plugs firing then the exhaust valve is open. Check to see that all valves close at the top of the compression stroke and that the rotor is set to fire each cylinder at that time..
David Werblow

Remove the pertronix
Len Fanelli

Replace the rotor and distributor cap first. They do go bad from time to time, especially the rotors. Use one of the red ones for maximum reliability. Next try replacing the condenser. If that doesn't clear it up, re-fit the points and see what happens.
Steve Simmons

I've never known the Pertronixs to be anything other than GO/NO GO...what is there there to be intermittent?
Gene Gillam

here are some vacuum gauge troubleshooting tips. when you inspected the distributor cap did you remove the plug wires from the cap and check the ends and the cap barrel? just curious..regards, tom

from a wiki you know it is gospel...The most likely cause is from: 1. Incorrect timing, the timing issue could be caused by bad wiring/ or bad ignition, skipped tooth on the timing chain 2. Incorrect fuel to air ratio, bad fuel filter, low fuel pressure-caused by weak fuel pump. 3. stuck or burned valve. Most cars will have the same cause for backfiring, as long as it's an internal combustion engine it shouldn't differ...
tm peterson

Well I got it running! Darnedest thing though. After ordering points and a condenser, I removed the Pretronix parts while I was waiting. They looked dusty/dirty so I wiped everything with a clean rag and reinstalled them. The car started right up and ran smoothly! I told the owner to keep the new points and condenser handy he might need them soon.
Bob McLeod TD 5618

Bob, see I had a similar problem that turned out to be caused by the Pertronix magnet collar pushing the rotor up against the carbon brush in the distributor cap. Bud
Bud Krueger

Very informative Bud. Just out of curiosity how long had that rotor been on prior to failure?
Bob McLeod TD 5618

Don't know if I can answer that, Bob. I'll try to track down some archiving tomorrow and see if I can get an idea. Bud
Bud Krueger

Bob, as best I can tell the rotor had been in use for about 2,000 miles. But, hang on a bit. I may have reason to jump back in on this issue. Bud
Bud Krueger


I wonder if this thread is in/on the correct forum...!

Bob is talking about an MGA, or a MG TA....!

Or, I mis-read his beginning post.

DrRx. TD 823

This thread was discussed between 20/03/2014 and 25/03/2014

MG TD TF 1500 index

This thread is from the archive. The Live MG TD TF 1500 BBS is active now.