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Help! Oil issues

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Bristolbadger:
Alright guys, I need some expert help again

After a joyous few trouble free months on the old 750 bob - I finally got round to syncing the carbs and with the new points and reg/rec she's been running so sweeet... however it ended last wk after a evening ride resulted in the RAC and flatbed Greg to recover me home  

15 mins into a decent duel carriageway blast I stopped at some lights, lost power and died then oil puked out from under the oil tank cap. (Not the breather)
I moped it up checked the level and still seemed good, cooled down for 10 then she fired up with no probs so I gingerly carried on and all was good, no exhaust smoke or odd engine noises. 3 miles later I stopped to check things over and the oil upwelled/puked again and had been leaking slightly.

After some thought I guessed I might have over filled as I'm running a custom tank, 2.2L but the level was good.
Next day I fired her up again and after 10mins of idling and seeing oil returning to the tank a 1st gear pootle down the road I had another look in the oil tank cap and it welled up and overspilled again.

I dropped the oil and removed the oil pump and filter and had just over 2L - I lost a fair bit when it puked each time. No bits of anything in the sump pan or pump screen. I've since checked the pressure relief valve and it's all good, not stuck and piston moving freely, likewise with the oil stopper valve.
The filter was fairly grubby and needed a change.
The feed and return lines are clear and free flowing likewise the crank case hose and the head breather hose.

I'm a bit stumped, what else should I be looking into?

Oddjob:
Not a 750 expert and never professed to be but I'd be checking crankcase compression, has the vent pipe been blocked or kinked. Run it detached and see if it does it again.

Bryanj:
Sounds to me like you topped it up when it had been stood a while and oil tank had drained into sump

Johnny4428:
Yes as Bryan says, have checked mine after short run in garage and only half way on dipstick check another time and up to full mark without any topping up.

Bristolbadger:

--- Quote from: Oddjob on June 02, 2023, 03:00:51 PM ---Not a 750 expert and never professed to be but I'd be checking crankcase compression, has the vent pipe been blocked or kinked. Run it detached and see if it does it again.

--- End quote ---
No kinks or restrictions that I can see and firing on all four with power until she pukes and stumbles.. will put everything back together with fresh oil etc and see how she goes

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