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MG MG Y Type - Hot starting

I have a YB, which was restored by a previous owner, after many years of storage. Since its restoration, it had covered only about 200 miles up to the time I bought it 2 years ago. I completed the restoration and started using it regularly towards the end of last summer. As far as I know, the engine is in its original specification, not converted for unleaded fuel, so I use an additive.

Although the engine ran reasonably well, it was a bit lumpy on tickover and seemed to be running rich, despite the jet being screwed right in. I had the well documented problem with hot starting, due to fuel vapourisation.

So earlier this year, I made and fitted a heat shield (as Jack Murray's drawing) and insulating blocks between the carburetter and manifold. As an added bonus, I painted the exhaust manifold silver. (I remember from O level physics that light bodies radiate less heat.) While the carburetter was off to fit the heat shield, I overhauled it with new DZ needle, jet and seals.

I initially thought that this had cured the problems. It started more easily from cold and the hot starting problem seemed solved. It certainly runs more smoothly and seems to have more power.

On Saturday, with the air temperature in the high 20s C, I took it for a 15 mile run before refuelling at the local petrol station. It had spluttered a little over the last half mile or so, but kept running until I switched it off.

Embarassingly, it would not start after I had paid for the fuel. Fortunately, the forecourt is on a slight slope and I rolled away from the pumps and managed to bump start it. When it fired, there was a loud bang from the exhaust and I got it home, albeit rather roughly. After an hour with the bonnet open, it started without a hiccup.

Yesterday, I took it to a local show, approximately 20 miles each way. Despite having 3 passengers and a full boot - chairs, picnic, etc - it pulled well and never missed a beat. The air temperature was much

Can anyone suggest what I might do to cure this problem?
M Long

Now you have sorted the carburettor, maybe you should look at the ignition?

The coil and condensor can go "off" when hot and the loud bang in the exhaust on startup may suggest a timing problem?

I'd check the condition and correct fitment/polarity of the coil first. maybe you can change it with a "known to be good replacement" just to diagnose the problem.
Willem vd Veer

Yes Willem is correct. How hot is the coil? I have had the issue where as a coil begins to fail it will get very excessively hot so lick a finger before you try to touch the body of the coil. If it is hot then your coil is begining to break down.

For condenser failure, open the points and if the points have a spattered appearance, then the condensor is begining to fail. It isnt unheard of but they are generally extremely robust and seldom fail.

Check too while you are there the continuity of the low tension lead from the dtributor to the coil. If this is old and decayed, fit a new one.

Paul
Paul Barrow

I could be a failing coil, or a bad condensor. On hot running old cars the condensor can be relocated to the coil.
I might be vapor lock which becomes more prevalent when mathanol laced petrol is introduced. We have had it here for years and it cause all kinds of problems.
Two years ago, I had to replace many of the brass fuel bowl floats in old carbs. in MGs and tractors. The meth-petrol eats away at the solder which joins the upper and lower float halves, and they fill up with petrol and sink. Pull the float and shake it to see if there is any liquid inside.
S.R. Barrow

This thread was discussed on 06/06/2011

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