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MG TD TF 1500 - Preignition

I just bought a 1954 mgtf and find that after the engine reaches running temperature and you turn it off it does not want to turn off. Is this typical of MG 1250's? Can it be anything other than possible carbon build-up in the cylinder heads?

Rick Beers
Redding, CA
E.R. Beers

I have read here that lowering the idle speed will help. Or using higher octane fuel. But just letting the clutch pedal out in say, second gear just moments after turning the key off will probably suffice. Seems like a pretty common problem, but not serious enough in my opinion to pull the head.

The float bowls have plenty of fuel in them and there's enough of a hot spot to ignite the mix, mine seems to run backwards when I turn it off. Kinda makes one wonder if there's a small burn even before the plugs fire at idle when the ignition is on, eh? Ah, but I'm happy with 'er anyway. Such a blast from the past, when cars smelled like cars, and you had to look under the hood once in a while - like daily.

Sorry I didn't have a better solution for you. I'm not sure if I want to squirt water in the carbs while running to steam out the carbon, but it's been done, I'm sure. Might be worth a try if the run-on bothers you. Maybe have someone look in the combustion chambers with a little camera thru the plug hole for likely suspects of hot spots. I presume those cameras are available to mechanics now, since they do it inside of you when they operate on your body. They probably even have little grinders and wire brushes to polish stuff they find.

I'll contin
Tom

Oops, dang machine. Or dang fingers.

I'll continue to let the clutch out. And appreciate the way my more modern machines run too.

Must be the lacquer thinner, I'm not usually so chatty.
Tom

http://www2.mgcars.org.uk/cgi-bin/gen5?runprog=mgbbs&access=&mode=archiveth&subject=8&subjectar=8&thread=200309300131551071

There was very recently a very long discussion about this- I couldn't find in the archives, but it is there somewhere- just dig around. Any car that doesn't have a postive fuel cut-off can tend to run on for many reasons, including idle too fast, carbon, sharp and hot edge in the combustion chamber, too low octance gas, etc. If it is running well, I would just do what you are doing to make it stop and forget it. George
George Butz

Hi Rick,

I've set my TD to run at 1000rpm on tick-over, which lowers to 800 when I depress the clutch pedal. If I turn the ignition off at 1000rpm it overruns, so what I do is put my foot under the throttle pedal and lift it, slowing the revs right down, then shut off the ignition.

Mike.
M Christie

I think the “run-on” or post ignition is a very common problem with TFs. I feel the pressurized radiator and the very close confinement of the engine tend to make the engine run hotter that the TD and thus more prone to post ignition.
David Werblow

Do the throttle shafts need rebushing? It is hard to set the idle, & mixture when the throttle shafts are worn.Rebush the throttle shafts. Set the timing to 5-8 degrees BTDC, set the carb. jets to .072" below the bridge in the carb. Then close the throttle plates until the idle speed is much lower, 500-600 or so.
Len Fanelli

This thread was discussed between 03/07/2007 and 09/07/2007

MG TD TF 1500 index

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