MG
The Classic Marque

Those valves work well, but the size needs to be matched to the engine size.
A wrong sized valve will result in oil being drawn into the manifold.

Paul, That’s exactly what was happening. As I increased the revs the strobe was showing a retardation, the distributor was moving by the vibration. Once reset and tightened enough it shows an advance when revved as it should. Hope I haven’t wasted your and other contributors time but I have learned a lot from this thanks again Trev.

A modern one should be fine, I'd have thought, and less likely to fail. Yes, should be central so air flow has the same effect on both halves of the engine even though it is pretty small, which is why both carbs have one.

Incidentally does the catch tank have an outlet and where does it go? A comparatively cold surface like that would encourage condensation, like in the long oil filler ...

Thanks for your feedback Paul. Using a PCV is the conclusion that I was coming to. As pucker MGB PCVs are no longer available at a sensible price I did wonder about using a 'modern' one like this with a suitable tapping/fitting in the brass plug in the centre of the manifold. I understand that it not advisable to use one of the ready tapped ones either side of the centre.

No through-flow ventilation hence nothing to take condensation away hence mixing with oil and the sludge.

If the carbs don't have PVC ports you really ought to fit a PCV valve to the inlet manifold somehow. The factory PCV valve used adapter 12H1405 with a sealing ring, you may be able to tap the manifold for that. Alternatively you could go back to the system used before PCV which is a...

I thought you meant it was retarding while revved.

Thanks for all the comments, think it’s sorted now. Originally the electronic ignition system had come loose that was easily fixed. It improved things but was not getting the advance I was expecting. Pulled the dizzy again and all looked OK. Reinstalled it, set the timing up again using the new to me strobe light raved it up to 2500 revs and the timing had retarded. What was happening was the di...

In the process of rebuilding my 18V engine I found that the catch tank connected to the front side chest cover with the breather tube was full with sludge, see image.

Clearly I would like to prevent this happening with the newly built engine, but how?

The rocker cover does not have a vent tube but does have a ventilated oil filler cap. The twin HS4 carburettors, with K&N filters...

Even with a dial back light, and even if the control is in the 'wrong' position, the timing should still advance when the revs are raised unless the control is being moved at the same time. Unless the light is faulty ...

Cheers Trev. They have their uses but can be confusing at times to a new driver. I have taped mine in the fully back position. Unfortunately the one I have doesn't have a click into position wheel it just rolls around. I've been caught a few times where I thought it was right back but had accidentally bumped it round a bit--very frustrating, so it's got taped up on zero. and I just use it for ba...