Norton Villiers DO7 info

The fact that it will only run on choked suggests that despite your efforts in cleaning the carb there is still an obstruction somewhere or that there is an air leak weakening the mixture after it has left the carb , so check any manifold joints and flanges for distortion. 

Another possibility is that the fuel level in the float chamber is too low so check that the float is correctly positioned on its needle.

You mention fitting a new piston and rings but don't mention the bore. Has the engine been rebored and fitted with an oversize piston and rings or are they standard components in a worn bore. If the latter was the bore checked for ovality and "belling" and was it honed or glaze busted before reassembly?

I didn't immediately recognise the D07 designation but I now believe that it refers to one of the Villiers Lightweight family more commonly known as the H507H or H-1.

If that is correct the points gap should be between 12 and 15 thou, the plug type a Champion L10 (L86) or equivalent and the plug gap 20thou. The tappet clearances should be 2thou inlet and 6 exhaust.Ignition timing 5thou or 20 degrees BTDC

Thanks Wristpin, it gives me a few pointers. The Bore is standard and I was just going to fit new rings to try to stop the oil getting to the top( but the supplier sent the full piston set so I fitted it.. I haven't checked for ovality etc which I suspect could exist .Don't think the DO7 is the same as the H SERIES as the points gap is definitely 18 thou according to the stamp on the flywheel. It is however a Villiers I suspect early 60's lightweight. Tried the plug at 20 thou and at 12 thou the latter gives best result but I fear will soot up quicker. Just put it back together today so will try it tomorrow.

Thanks for your help

After further research and an exchange of emails  with another forum member I agree that the Do7 is not an H series , it is suggested that its origins may lie with BSA before the amalgamation with Villiers.. 

I would think that your new rings may take a while to bed in to the existing bore particularly if you didn't "rough it up". Something worth checking is that the crankcase breather is not gummed up and permanently open. It needs to be able to shut and seal on the piston upstrokes to create some negative pressure in the crankcase which helps in keeping the oil away from the top of the engine

Breather appears to be working as trace of oil and gas is being emitted, about try again if I can sort the Recoil starter out which seems not to be engaging, otherwise I'll have to revert to the rope.

Breather. It would do that if working properly or if it is stuck open. You need to be sure that on the piston up strokes the ball or reed is closing and sealing to create negative pressure in the crankcase.

Recoil starter. I remember that pattern of starter as being a bit fragile and back in the day more often than not those engines would come in minus the recoil and with just the drum to wrap the rope round.

Don't think breather is stuck open. Have tried repairing/modifying the recoil starter but still can't get it to engage.  Anyway I'll have to revert to the old rope trick. 

If the breather on your engine is of the type with the screw in filter and a nylon ball it would be worth unscrewing it and giving it a good swill round with petrol. An image will help.

If your starter is of the type relying on friction to move a pawl outward to engage recesses on the drum it could just be over lubrication reducing the friction needed to eject the pawl; or general wear and tear doing the same.  If the latter it is sometimes possible to increase the friction by adding a fibre washer or just roughing up the steel ones. It will help if you can post an image of the assembled pawl mechanism - looking from the flywheel side into the starter .

That's fantastic you've answered the question what was the fibre washer for that fell out with all the other bits. Also I've been smothering the thing in oil obviously wrong.

Will get back to fiddling after the weekend. Thanks for your continuing help.