General => Douglas Motorcycles - General Discussion => Topic started by: Ian on 14 Feb 2013 at 02:29

Title: Hot air tube for OC
Post by: Ian on 14 Feb 2013 at 02:29
I have always had problems with my OC and carb ice. It runs great for a while and then except for really hot days suffers, fouls plugs, etc. When you stop it water runs out from the outer skin of the manifold.

It has a tube from the exhaust on one side to the inlet manifold on the other - quite a long track. I have used a copper tube but the diameter is quite small. I would like to put a larger diameter pipe across (the lugs are about 16mm OD).

I was thinking flexible wound steel tube would be a good solution - but I have no idea where to get it from. Anyone got any ideas ?
Title: Re: Hot air tube for OC
Post by: Doug on 15 Feb 2013 at 04:03

You are looking for flexible metal duct. I did not realize until I looked, but it can be had in smaller sizes. Generally I think of it in the context of home made automotive exhaust systems! But a 5/8 inch i.d. tube in galvanized steel can be had from McMaster-Carr (, search part number 5262k15) Can also be had in aluminum and stainless, but not in the 5/8 inch size.

A cheaper solution may by flex electrical conduit (known as BX here in the USA), though this is not fluid tight. Probably the 3/4 size is what you need.

Also for a semi-rigid but bendable alternative you may want to investigate the tubing used to connect natural and propane stoves to the gas mains. The ribs on this all metal tube are quite pronounced, so probably the least attractive solution.

You could probably scrounge a bit of the last two for free to try and see if hooking up the original carb heat system makes a difference, prior to investing in a more permanent and workmanlike tube.

Title: Re: Hot air tube for OC
Post by: Ian on 15 Feb 2013 at 04:05
Thanks Doug !