BSA Owners' Club Forum

The BSA Workshop => Singles => Topic started by: Phil C on 27 February, 2018, 13:45:24

Title: 1. Air filter, and 2. carburettor
Post by: Phil C on 27 February, 2018, 13:45:24
I took the air filter off my 1965 B40F this morning. Inside the outer metal mesh are two slightly finer metal meshes, and sandwiched between them is a piece of some kind of cloth. Out of interest, is that a normal set-up? 

Also, I'm going to take my carburettor (Amal Concentric 626) off to see if I can solve why my bike refuses to run without a bit of choke and yet has a black sooty spark plug. I know nothing about carbs other than what I've read, but I have some info from Amal (thanks again, Julian S). My stupid question is: when I start to take it off, should I first remove the cables from the handlebar levers, or leave them attached even when I take the top cover off the carb? Should I just leave them attached both at the lever end and at the carb end, even when I take the slides out of the carb?

Thanks in advance,
Phil (novice)
Title: Re: 1. Air filter, and 2. carburettor
Post by: AWJDThumper on 27 February, 2018, 17:59:41
The filter sounds normal to me and exactly the same as on my C15.

If you unbolt the carb from the bike, you can then take the top cover off to separate it from the carb. You then need to separate the cables (assume you have choke slide fitted) from the carb. The choke slide should just unclip. To unclip the throttle cable you first need to compress the spring and then, after removing the needle, unhook the cable.
Title: Re: 1. Air filter, and 2. carburettor
Post by: A10 JWO on 27 February, 2018, 18:03:21
Fair bit of research required here. Search Amal on Youtube first, buy some carb cleaner in an aerosol. Everything must be spotless. Cables slide out top of carb. Take photos on mobile phone as a reminder. Just come back as and when, consider a new gasket set. regards.
Title: Re: 1. Air filter, and 2. carburettor
Post by: AWJDThumper on 27 February, 2018, 18:49:19
The first thing I would do is to check the carb settings: main jet, pilot jet, needle pos, throttle slide and needle jet. They should be approx: 130, 20, 2, 3 & 0.106, respectively. The main thing to look out for is how snug or loose the throttle slide is in the bore and whether there are any obvious signs of wear. Also make sure the flange on the carb where it bolts to the engine is perfectly flat (use straight edge) and has not become distorted.
Title: Re: 1. Air filter, and 2. carburettor
Post by: Phil C on 28 February, 2018, 14:11:54
I guess I should own up. Having removed the air filter, this morning I peeped into the carburettor and realised that what the previous owner told me was full choke was actually no choke. So that  might explain the black sooty plug problem. And why I can't decide whether to be cross or just embarrassed. Relieved anyway, as it does at least make more sense now. Very sorry to have wasted people's time.  Phil (novice, as you can tell.)
Title: Re: 1. Air filter, and 2. carburettor
Post by: AWJDThumper on 28 February, 2018, 14:37:39
If it's any consolation, I once rode a newly acquired A10 twin 150 miles home on full choke thinking it was turned off. My excuse was that on the more modern bike I normally rode at the time, the starting device worked the other way round ::)
Title: Re: 1. Air filter, and 2. carburettor
Post by: TIGER on 28 February, 2018, 14:42:50
Phil
Great you found the problem.
You anywhere near Staffordshire.
Love to see your bike when the weather improves
Regards
            Tim
Title: Re: 1. Air filter, and 2. carburettor
Post by: A10 JWO on 28 February, 2018, 15:02:18
Been there, done it outside Gander and Grey on my new Commando ( memories )  ???
Title: Re: 1. Air filter, and 2. carburettor
Post by: Phil C on 28 February, 2018, 16:16:11
Hello again everyone, Just to say thanks for being so understanding!

Tim, I'm afraid I'm nowhere near Staffordshire. I'm down in South Devon, on the edge of Dartmoor.

Phil.
Title: Re: 1. Air filter, and 2. carburettor
Post by: Phil C on 28 February, 2018, 16:23:25
I am a little bit surprised though that it wouldn't run on full choke (what I thought was no choke). I'd have thought that on full choke it would have run but with high rev's. Not necessarily so, I guess?  Phil (novice.)
Title: Re: 1. Air filter, and 2. carburettor
Post by: AWJDThumper on 28 February, 2018, 20:54:16
The main effect of the enrichened mixture due to running on full choke would be to effectively advance the ignition which would make the engine running very lumpy and unwilling to rev.