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2024-06-11, 20:02:05
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2024-06-08, 18:30:04
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1922 Douglas 4HP B22 Intake Manifold Question

Started by wheelhousegarage, 30 Nov 2022 at 17:01

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Hello Douglas motorcycle community! My name is Bill Wheeler and I am brand new to this forum. My father and I own two Douglas motorcycles and enjoy learning about them.

In the attached photo, what are the threaded fittings on the intake manifold for? I found a photo of another B22 that has some hard lines coming off of them, but I wasn't able to figure out where the lines travel to. Is it a breather with optional air adjustment? Your assistance is much appreciated!

P.S. I also host a weekly show on YouTube called "A Bike and a Beer" where I feature rare vintage motorcycles every week and this bike will be featured this Saturday! Tune in and subscribe if it meets your fancy  :D 


Have you investigated where those fittings lead to inside. ?
Some form of (primitive) hot air feed into an internal heat exchanger perhaps  ??
With an option to switch off for warmer weather ...

Thought your name looked familiar.
Enjoy your work ...

P.S. Another pic shows its a bleed off the exhaust system - so pipes hot gas through there.


That was my best guess as well from studying that other bike - I appreciate your input! I'm pretty sure the holes just go straight into the intake manifold with an option to close the right side (front side).

Thanks for your kind words too!


I'd think there should have been a tube inside, connecting those 2 connectors.
Unless there is a (sealed) connecting tunnel in the alloy casting itself. ?
So the hot exhaust gases could give some heating to the fuel/air mix.
Essential for cold weather running ?


Here's my new video about this bike if anyone is interested.

Thanks again for your help!