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MG TD TF 1500 - Boiling fuel


My TD mkII has developed a problem when getting warm. When reaching normal temperature around 80-85 degrees celsius, it starts to misfire, which I believe is caused by the front carburator (H4 type). If I am very careful with the accelerator the engine runs normally, but as sopn as I press it just slightly it does not run on all 4 cylinders. I have installed at heatshield and spacers about 8mm thick to increase distance to the exhaust manifold, but it doesn't seem to change much. The problem is fixed by opening the hood for about 15 minutes or more, so I'm pretty convinced the problem is caused by heat, but i've ru out of ideas.
Can anyone help?

As usual thanks in advance
Torben Olesen

If all else fails, have the manifold ceramic coated.
Dave H
Dave Hill

I am no expert, but perhaps you are running a little lean. If you pull out the choke does it help? Same applies to the restart when hot. someone else with more expertise please comment.

James Neel

There is also manifold and head pipe insulating "tape" that motorcyclists use to wrap their manifold to keep from getting burned. Do an Ebay search of manifold insulation. Looks much like seat belt webbing but very different material. You could also wrap the metal pipe that leads to your fuel pumps.
John Quilter (TD8986)

You should not need any of the band aid fixes suggested here for a normally aspirated, properly tuned and maintained TF while driving. If after a run your heat soaked engine compartment causes your fuel to boil and vapor lock, just pull on the choke for starting and by the time you leave the parking lot you can stow the choke and proceed on your way in a normal fashion.
You may have an issue with improper timing, mixture too lean or even dragging brakes.
Once you get it all sorted you won’t need any of the above suggestions.

Good luck.
Regards, Tom
tm peterson

I am with Tom on this one. Where I am it can often get over 100 degrees. Normal running its fine but after a shutdown for a few minutes the choke trick will get you back running again and the miss fire should subside quickly.

I did once get a vapor lock at 8,000 feet on a 95* day but I think that was a different story. In that case I did have to drive with the hood open until I came down a few thousand feet.
Christopher Couper

Hi again

The problem I expierince happens during driving especially if running at low speed and thereby not getting that much cooling.
The carbs have been rebuilt and adjusted and I'm using a CSI electronic ignition, so I doubt it has to do with tuning.
I'll try the choke trick as soon as I get the chance, and let you know.
Thanks for your feed back

Torben Olesen

Hi Torben,
Check the oil level in dashpots
It may also be a stuck carb piston.
Read (and buy) the excellent book from Paul Ireland
Do you know that summer fuel is less volatile that winter one ? By new fuel.

Because the problem has just appeared, I would say, it is a failure. No additionnal modification should be necessary to your engine.


LC Laurent31

Sounds like hot ignition failure? Change the coil? George
George Butz III

Hi Everyone.
First of all thank you all for your suggestions. I started up with trying the choke thing, but that didn't change anything. Then minor adjustments to the carbs were done, which surely made a difference. I then decided, as George suggests, to try a brand new ignition coil and that seems to have cured what was left of my problem. Next week I'll have the carbs fine tuned at a garage nearby, and then hopefully will be back in business.

Torben Olesen

This thread was discussed between 15/07/2021 and 25/07/2021

MG TD TF 1500 index

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