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MG TD TF 1500 - Miss fire when working hard

Over the past few years I have been plagued with a miss-fire mostly when the engine is running hot, ie after a few miles on a main road at about 55mph, coming to a roundabout and then setting off the miss would start, the more you pushed the worse the miss. I have tried everything all suggestions on this site including fuel starvation to ignition component change. I then came to the conclusion it will be something stupid. I drove the car to Jersey via Poole car ran well most of the way with little or no miss-fire, when in Jersey refuelled there and all week never missed a beat, I then thought Ethanol was the culprit as Jersey does not add ethanol, but there is a 40mph speed limit, but on returning to England still did not miss until refuelling in Nothhampton I then began a long pull from there and the miss fire returned, I kept stopping let the car cool and then set off again all ok for about 50 miles the miss returned. I managed the limp home. I then thought , what havn't I changed, it then dawned on me the only thing I hadn't changed were the plug caps, these I had replaced with new ones 10years previous during complete rebuild. I duly replace with none resistance type. Sure enough the car now runs fantastic with no miss fire what so ever seems like a different car.
Total miles covered Jersey and back 830 miles. total miles driven with intermittent miss-fire 10,000.
It's the simple faults that trip us up.
Thomas WELLS

Yes indeed. $50.00 parts down 747s.
MAndrus

We had an intermittent with the TD. Turned out to be a slightly overlong plug lead touching the block.

Matthew.
M Magilton

Have had the same problems.If it missfires and shoots it might be the cond and if it only missfire under load it might be the coil.
YS Strom

Sounds like the carb bowls are getting hot and a vapor lock situation is occurring. If the gas starts to boil, that's what will happen. PJ
Paul161

I changed the condenser and coil several times including ones from a normal running TD as I did everything else on the ignition system apart from the plug caps as I thought plug caps could not cause the miss, how wrong I was.
The car carb. bowls were always cool as the fuel evaporation naturally does cool the fuel system I never had a vapour lock in the system although I replaced all seals and glands in the carbs, perhaps this is why the car is now running so well.
It must have been the resistors breaking down when becoming hot there was no continuity when tested and just a small reading on I cap. I replaced with none resistor type caps so no resistors. the originals had 10,000 ohm resistors which is normal for these engines at that time (1950).
Thomas WELLS

This thread was discussed between 15/09/2015 and 17/09/2015

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