I learned a lot from previous wet sumping posts and the references members forwarded and forgive me if I missed something but the functioning of the straight through ones escapes me. If the valve is not closeable I understand that pressure is supposed to do the job but on my M21 I doubt if that could be achieved. Are the valves with a lever a more certain repair? I realise the forgetting to switch it on part but my old bike has lots of fiddling anyway with ticklers, advance retard, 1/8th throttle, petrol tap, just over TDC so adding one should not be difficult.
Get a tap with a magneto overide switch.
I fitted one of these automatic anti-wet sumping valves (https://www.ebay.co.uk/itm/396981805100?_skw=BSA++B31%2F33.%2FM20%2F21+ANTI-WET+SUMPING+VALVE.STAINLESS.MADE+IN+ENGLAND&itmmeta=01K45T444KDNTSPQ652T8YGHJ3&hash=item5c6df5a02c:g:OnwAAOSwOAZZgb6v&itmprp=enc%3AAQAKAAABAFkggFvd1GGDu0w3yXCmi1drsalXtvpLb5expV94F0uQIhtm7fyyI2gCXLH5Q%2FfbHp4oeT0sZ0nBnCmTvpRtxf2tfTytQ7JX5fMQxzyWxwJaCXj%2F9kZ09%2BeJqvMw3FkrFChcCSzhwyi1KFmWnAoh4yxU%2FyE4fx7IrPZY6LSIMTNmlYWTplnjGPu3cZXtieT5o2TSZ2epM5IrMJgepJQrt6jCz8vHEn7sjzR7MwtNWbo4Z5UFapoofqpOnWn0dqKMEsAolFK%2Bx4pET0Pwj3Z1jPDZSd94WCWlP2Vc9DjcETunG3dA%2Bf1wJ50nsFUHHxgzIFjJ2nCDxEwrMAWBp59AIw0%3D%7Ctkp%3ABk9SR7LCkLqhZg) 4 years ago and have had no issues whatsoever. It works very well. Other users views may differ.
I fitted one of these. Take a look here.
https://www.themagnetoguys.co.uk/oil-tap-with-cut-out-switch
Quote from: Andy Kay on 02 Sep, 2025, 21:52 I fitted one of these. Take a look here.
https://www.themagnetoguys.co.uk/oil-tap-with-cut-out-switch
Not so easy on a Magdyno where the M01 mag has no ground connection in the points cover. I believe that modified points covers that provide a connection for a kill switch can be obtained though.
Just checked, same place : https://www.themagnetoguys.co.uk/points-caps-with-cut-outs#One (https://www.themagnetoguys.co.uk/points-caps-with-cut-outs#One)
Gets pricey though at over £100 for the two of them.
I'm not a fan of taps on the oil feed, I've found seating the ball valve, lapping the pump faces and a run every week or two is enough to stop wet sumping. But if you do fit a valve I've seen one with a long lever that gets in the way of the kickstarter and another with a bright red strap round the kickstarter (it looked like an outboard kill cord).