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MG TD TF 1500 - Engine stall when car starts

Hi,
Well hidden failure. It only happens when the engine is hot but sometimes only. Stopping the car for just a traffic light or even a cross road for half a second, the engine idle is good but when trying to accelerate and drive in first, the engine runs on one or two cylinders for a a couple of seconds and then stall.
It can restart immediately or only after a few minutes.
Have been driving with this rare failure for long. Beeing through 3 coils et 3 condensers, different plugs. The engine compartment is quite cool. Carb bowls, hoses and fuel pump is around 40°C.
Carb pistons are not sticking, at least when cold.
Points look ok and gap is adjusted. Distributor cap and rotor arm are new.

Any idea ?
Laurent.


LC Laurent31

Carbs may be getting heat soaked at low speed. Try enriching the carbs a quarter to one half flat and see if that makes a difference.

... CR
CR Tyrell

Laurent,

This could be a problem with the engine ground strap, check its condition and that you have a good clean connection on each end.

John
J Scragg

Had a similar problem, but after gentle polishing of the carb throttles it worked well.

Might also be worth trying with a leed from the battery direct to the didtributer.
YS Strom

Progress today,
Ground strap is tightened, strong thick and short.
Instead of a direct connection from battery to coil, I installed a lamp connected to the coil and in front of my eyes. I could never see any blinking of this lamp.
Then drove around the blocks. Many stops. So that I could feel the increase of the phenomenum and get back home before total failure. Today's temperature was 29°C (84°F) and the engine was stabilizing at 85°C (185°F). In my opinion, it seems quite normal for a stage 2 engine and short runs in first and second, or third sometimes.
Back at the garage, I stopped the engine and swapped for another coil, ready for that test. Less than a minute and the engine did not start.

Then Off with air filter and pipe, carb pistons. So 10 minutesafter and I could clearly see fuel bubles escaping from the jets drowning the carbs.

So now I have to fight against overheating of the fuel circuit.

The problem is that I have already a heat shield, carb spacers and insulating strip on the down pipe of the exhaust.

Timing is set at 9° at idle and 27° maximum which did not occur today.
Shall I modify the shield ? Shall I work on the air flow of the engine bay ? Shall I work on the temperature of the engine ? Insulation of the bowls, hoses, pump... ?
Any advice ?

Laurent.



LC Laurent31

Laurent: What's that item that looks like a barbed hose fitting on the top left of your intake manifold?

If it is an intake what is it for and you should have it sealed off if not being used.
Christopher Couper

When it stops running, remove the float bowl lids and visually check the level of fuel. Also try opening the gas cap up and listen for a whoosh of air going in, if somehow the vent got plugged. What color is the rotor? All but the red ones are trash. George
George Butz III

Laurent,
I do not know how Lockdown affected you in France, is it possible you still have winter fuel in your car. If so it will gas more readily than summer fuel. I noticed my Tf was acting up until I filled up with new CHEAP fuel.
Ray TF 2884
Ray Lee

Laurent,

Can you make sure that the washer in attached image is in place under each banjo connector of the overflow pipes. BTW. These pipes look a little messy.



John


J Scragg

Thanks to all.
Chris : Yes, that was probably an intake for vacuumm advance. Anyway, it is plugged.

George : The vent is OK, the fuel level is also OK, D Braun Method. But it is boiling when hot!
The car runs OK when cold or in winter or even for high speed but low speed, stops, city drives, make the carb to hot.

Ray : that's right, the fuel is probably dated from last automn. And that could be a reason why this problem is not systematic every summer. Good idea.

John : both washers are OK Never had problem with this.

I'm also thinking about an air scoop under the rad to fresh up the carbs.

Laurent.
LC Laurent31

Laurent,

I had similar problems and found it was due to old gas (E10). It wasn't even that old. Try draining some fuel from the tank and look for water drops.

Jim
J Barry

I only use E5 for many reasons discussed elswhere.
Ray, why do you insist on CHEAP fuel ? Is it less prone to vapor ? Anyway, fuel varies alot with countries.

Made a quick prototype scoop today. Good results (feeling only, no measurement). Of course the scoop is of no use when speed = 0, real traffic jam. But it is efficient in slow drives and frequent stops of cities.
But beyond this, I gave more static advance. Beeing now at 12° at idle and 30° at maximum RPM. Same weather, same drive and the engine temperature is now 5 to 7 °C lower (175°F). And I had no problem.

Laurent.







LC Laurent31

I am not a big fan of heat shields. Proper coating of the exhaust manifold and proper tuning/gas should not require them.

I wonder if the heat shield is actually exacerbating your problem when warm. While it theoretically should isolate the carbs from direct heat it is also putting a hot item much closer to them.

Anyway it sounds like you have a fix with changing the timing.
Christopher Couper

Sorry Laurent,
only joking about the fuel. It is just that as vehicle use has dropped our fuel has gone to £0.9 a litre from a high of £1.20.
For our American friends that is about $5.20 to $4.80 per US gallon.
That is why we have small engines in small cars!
Ray TF 2884
PS my TF does around 30 miles to a gallon but my MX5 (Miata) manages 50
Ray Lee

I had my TF1500 distributor rebuilt, when it came back the instructions said 10-12deg BTDC at idle.

I tried to get the idle down to about 700 RPM to check the idle timing.

Even before the rebuild it never overheated, but here it rarely goes above 90deg F.

Peter
P G Gilvarry

If it's a TD as an experiment, try running it with the RH side lower hood panel off to increase ventilation and airflow in the engine bay. I've also, on my Morris Minors, wrapped the float bowls with the foam insulation you use on house hot water pipes. Hold in place with a zip tie. I also agree that winter fuel is more prone to vaporization than the summer blend.
John Quilter (TD8986)

Back in that earlier pic. with the carbs pulled apart, the jet tubes appear to be a long way down the hole, they should be up around .060" from the bridge---maybe it's possibly idling a tiddle too rich and gets too much of a gutfull as you take off when it's hot

willy
William Revit

Check that all the filters in the fuel line are clear - in the tank, in the pump and in the carbs. Plus any ancillary filters added by a previous owner.
Dave H
Dave Hill

I can say this that simply looking at the tank strainers may not be sufficient. Early on after getting TD-4834 on the road after it’s restoration I ran into a similar issue. I would find sediment in the pump and carb strainers and some grit caught up on the tank strainers. But certainly not anything that would restrict flow. A visual inspection of the tank before it was put back in service appeared that the tank was in good order. If fact, what was occurring was the fuel would be agitated while on the road or idling in the driveway. This would allow the rust flecks to cling to the strainers eventually restricting the flow of fuel. When the engine was shut off, the flecks would settle out of suspension and fall from the strainers. When inspected after only a few miles, the strainers would still appear to be clean however sediment could be visualized in the float bowls. I eventually got tire of the ritual expecting different results. I pulled the tank and went through the process of agitating the tank using nuts and white vinegar over several and was amazed how much crud was removed from a “clean tank”. I then sealed the tank and had little issues since.

Bill Chasser
TD-4834
W A Chasser

This thread was discussed between 26/05/2020 and 31/05/2020

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