My 652cc conversion runs well, is reasonably economical - 40-42mpg - but on a long run seems to burn a lot of oil - we have come over to West Wales and it has lost around 500ml in 180 miles but pottering around here has used none - is it something to do with running at higher road speeds and engine revs that is pointing towards knackered rings or poorly run in rings/barrels or valve stem seals or something else - it doesn't drip a fat lot of oil, is not losing anything from the head banjos and I put a new breather on it a couple of months ago????

I would suggest worn rings in the main, but look at the one way valve in the oil filler tower (as well as Valves, guides and seals).

Do a compression test and leak down test, and see what a manometer reading shows on crankcase vacuum.

Thanks for the response - the breather is a new improved from Roy so I would rule out crankcase pressure - I'm buying a compression tester when I get home but any other thoughts are welcome

Blue smoke ? Why do I bother asking !!!!!

What's a leak down test?
Edit
I looked it up
https://mobiloil.com/en/article/car-mai ... kdown-test
Clever I want one
Check ignition timing!

Why timing?

To advanced can cause higher pressure and blow by.

I'm sure I read it on here somewhere.

But I have been asleep since then.

I'll see if I can find it.

Ta da

viewtopic.php?f=7&t=5516&p=117372&hilit=%2AOil%2A#p117372

Not quite as I remembered it, but Sean mentions it here for an oily airbox.

I think I follow Kens logic but I don't have an oily air box - ( oo er Missus! In best frankie howerd mode)

yup however as its not blowing oil just burning it id be suspecting oil controll rings or some other issue with the bore or rings
if its burning it you will see it as deposits on the stem of the exhaust valve or as a tan buildup on the plugs

dont rule anything out do a maniomiter test ive seen those breathers not working at all due to swarf under the reed valve

Confused.com! Came back from Wales at the weekend and doesn't appear to have used much oil at all! What could possibly cause it to lose oil sometimes and not others???