Smoking Jubilee

Obvious stuff first .... flow back from the engine will always be a bit “ spurty” as the return works harder than the feed. Also have you checked the feed to the head? - is all the oil going there rather than back to the tank? 

Finally when you say you have fitted an anti wet sumping pump, is it different from the standard jubilee pump? 

Dan 

If too much, it can flood the rockers and the vacuum of the inlets is easily able to suck it down the guides giving a slow but steady increase in smoke levels. You can try blanking off the oil supply to the top end (if still a rubber tube, squash it shut with some mole grips) and see if the smoking diminishes. Don't do this for more than a few minutes else the cam followers may begin to run dry- not ideal on a lightweight. If the smoke does reduce, it suggests that there is too much oil going to the head. The Jubilee had a restricted oil tank fitting to push more oil up top, but with wear and tear it might mean you need less restriction? 

My Jubilee crankcase breather had been blocked with what looked like car body filler by a previous owner. I did not know the breather existed and the filler was the same colour as dirty aluminium casting so not easily seen. I had rebuilt the engine with new seals and I could not understand why the primary chain case was filling with oil at an alarming rate. Someone on this forum suggested a build up of pressure in the crankcase was pushing engine oil past the crank seal and that I should check that the crankcase breather was not blocked. When I found out where it is supposed to be of course it was blocked!!

I drilled out the hole (at the top of the rear of the crank case behind the inner primary cover) and inserted an 8mm copper tube to lead away from the engine and attached a rubber pipe to take any oil away in the direction of the rear chain. I check periodically that the breather is clear by blowing back down the rubber pipe and expect meet little or no resistance. Since this fix the primary chain case no longer fills with engine oil.

Dennis

Another thing that can catch you out is oil left in the silencer from when it was burning excess oil before the rebuild.  The best cure is a long run to get the exhaust really hot.  When the smoke stops, problem solved.

There is an oil flow diagram in the excellent Light Twins compendium, page 71 of the on-line  document. Look under the 'Technical ',tab,  'Light Twins'  and load the on-line document. Lots of good stuff in there.

Dennis