BSA Owners' Club Forum

The BSA Workshop => Twins => Topic started by: M Brook on 31 August, 2017, 12:11:51

Title: Different colouring of exhaust on a twin
Post by: M Brook on 31 August, 2017, 12:11:51
I have just bought a 1961 Godden flash and when I have run it, 1 exhaust down pie has gone blue, in colour the other has gone a light shade of yellow. what could cause this.

Thank you

Mark
Title: Re: Different colouring of exhaust on a twin
Post by: JulianS on 31 August, 2017, 12:25:55
Induction bias - one cylinder running weaker than the other.

Or ignition timing - one cylinder more advanced than the other due to mag problem.

Or both.

Stainles pipes tend to yellow after some use.

I would check carburation ignition timing tappets and adjust if necessary.
Title: Re: Different colouring of exhaust on a twin
Post by: M Brook on 31 August, 2017, 12:59:32
Ok Thank you for the reply. The Godden Flash has one Carb, so could this effect the 2 cylinders differently?

Can you give me more information on how the timing can be out for one cylinder and not the other?

Not doubting explanations  but just learning.


Thank you,

Mark
Title: Re: Different colouring of exhaust on a twin
Post by: JulianS on 31 August, 2017, 13:25:15
Differences in the induction track and cylinders can cause bias - see photos which are from The Book of BSA Twins by W C Haycraft Pitmans Motorcyclist Library series.

It is not unusual to find that mag points gap is different between the 2 cylinders, this can be caused by the manufacturing tolerance, photo 3 from Lucas service bulletin. It is also not unusual to find that the timing is slightly different between the cylinders, could be due to bad assembly, worn or badly shimmed bearings, worn cam ring , misalignment of armature etc etc. If too far out mag may need attention.

I would check all the basics of carb including carb to head joint  o ring and gaskets, points, plugs and see where it takes you.
Title: Re: Different colouring of exhaust on a twin
Post by: M Brook on 31 August, 2017, 13:34:43
Thanks for info, has suggested will start with Basics on carb.  And than check position of each piston with opening of points, before taking timing cover off. the book you quoted sounds like its worth having?

Cheers


Mark
Title: Re: Different colouring of exhaust on a twin
Post by: JulianS on 31 August, 2017, 14:18:24
The book is worth having if you can find one at a reasonable price - I got my copy before I bought my A10 back in 1973 - worth also getting a set of service sheets.

I would also make sure the exhausts are a good fit in the head and silencers to prevent air getting in.

Have sent you a PM please check under "My messages"
Title: Re: Different colouring of exhaust on a twin
Post by: M Brook on 31 August, 2017, 15:57:36
Hi
Thank you for your advice, I will let you know how I get on.

Mark
Title: Re: Different colouring of exhaust on a twin
Post by: EDDIE SIMPSON on 31 August, 2017, 22:26:49
from what ive been reading on the internet recently about k2f magneto care i would also suggest the slow death of the secondary windings and/or condensor. but if the bike runs well and is working. why fix it?