What the heck is this?

[Tim OConnor]

Can anyone tell me what this line is that goes from the back of the petrol tank to the front of the carb intake??

[cardan]

An extreme misunderstanding by a previous owner?!

I can't quite see, but Douglas commonly used a warm air muff on their AMAC carburettors, in which case you might find that the connection at the carb end doesn't go into the intake manifold, but instead into a gallery around the intake tract. If so, the other end doesn't connect to a fuel tap (!!) but instead to a collector of hot air off the exhaust pipe.

Leon

[Hutch]

Tim,

My answer is same as Cardan's who posted while I was writing this :-)

Certainly not standard!!.

Rear tap on tank is normally just a fuel drain tap and goes nowhere. Looks like you have an earlier AMAC carburettor (little bit hard to see in the picture) which has an exhaust heating jacket on it to help stop icing up of the carby under certain weather conditions.

The heating jacket has an pipe which is connected to the exhaust system on the inlet side and another which simply exits onto the road. These pipes are often not connected and the fitting in the manifold blanked off. You may have a later exhaust manifold without the fitting tho' as this method of carby heating was not used on all models. I will have a look at your earlier posting and see if I can spot it in your pictures.

I am not sure of the purpose of feeding the fuel line through the carby jacket like this ?? - very strange. I guess if you turn the drain tap on fuel will come out of the exit hole in the heat jacket and just goes on the ground??

I will dig up some pictures if you need them. The pipes for the heat jacket are shown in the 2 3/4HP parts list 194D and 170D. If you look in the 1920 Peace program brochure on page 12, you will see a picture of a slightly later AMAC carby with a pressed heat jacket rather than the cast / soldered to the carby body earlier version but it serves the same purpose to help stop freezing of the carby.

Many owners don't bother with using the heating jacket but it probably depend on where you live and whether or not suffer from carby freezing / icing up problems.

Hope this helps,

Cheers

Hutch

[Hutch]

Tim,

Picture of the outlet for the pipe to the carby heat jacket / muff on your bike As per above could be blanked off but hard to see in the picture.

Cheers

Hutch

[EW-Ron]

That actually looks like its running petrol into the inlet manifold ?

Could it be some PO's attempt at fuel enrichment for cold starting purposes ?? !!
Turn tap on - for 2 seconds- turn tap off.  Initiate starting process - run and jump ?

[Tim OConnor]

Thank you everyone!!