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MG TD TF 1500 - Missfire at low reves

Went for a drive to the local Hospital with the Car Club on Monday to show support for the doc and nurses. Nice safe trip but the TD was misfiring (like on 3 pots only)at low revs. Had to slip the clutch to get started and then over 1000 rpm it was fine.
Thought it might be the gas but I put in 93 octane and it has never been an issue in the past. I use it before it goes bad :)
Removed the plugs and they were a little sooty but biscuit underneath. Gaps were a little large so put them back to 22 thou. Dizzy cap was interesting. Carbon contact was flush with the cap body. Managed to remove it and it seemed the spring was missing?? Found an old pen and borrowed the spring and cut it to length and refitted the carbon contact. Now about 3/16th proud and had some springs to it. Refitted everything and she fired up strait off and no misfire. Could have been the plugs I guess but I think it was the carbon contact. Can't explain why it worked OK at higher revs though.






Rod Jones

Rod, any chance that you're using a pertronix with the magnet sleeve? Bud
Bud Krueger

Any chance you were effected by the drooping rev counter gearbox shorting on the distributor lead issue?

I can't remember if this is more prominent at low revs or all revs.
Christopher Couper

Sometimes a sight misfire can be masked at higher rpms. Dirty plugs can also certainly cause the symptoms you're describing. The missing spring definitely wasn't helping either.
Steve Simmons

No Bud,
I have only the original equipment in the distributor. I did make a change to the tach gearbox fixing to the dynamo. It Is now absolutely solid.
The broken un-sprung carbon contact in the dizzy cap I have seen before. This was a new cap 4 years ago. The plugs were new 2 years ago. New bumble bee wire about a year. I have 3 capacitors that I have tested in the distributor and all worked fine. Can't say for sure it was the contact causing the issue but it has definitely gone now.

Chris,
When the gearbox shorts to the dizzy - it all stops dead. Ask me how I know? :) This fix has resolved any problems in that department.



Rod Jones

I just went through the same issue. There could be many causes. Mine turned out to be a new air filter material I was using. It was fine at first but must have either compressed or plugged to restrict air flow very quickly. I went back to the old material after trying many fixes and it is now fine.
Ron Coates

This thread was discussed on 16/05/2020

MG TD TF 1500 index

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