The BSA A7-A10 Forum

Technical => Amal, Carburation => Topic started by: Simon59 on 05.08. 2019 15:37

Title: Are there any carb experts out there?
Post by: Simon59 on 05.08. 2019 15:37
I am experienced enough to know that poor performance can sometimes eventually be traced back to a worn-out carb, (or carbs as was the case on my Ducati 860), and that simply cleaning it up, fitting new jets and washers, etc. doesn’t fix any wear in the body of the carb. My thoughts turn to my ‘refurbished’ 276 carb as my plunger A10 rebuild progresses, because many bits of my bike have seen a hard life in the past.

I have read somewhere that the body of the carb can be bored out and then hard chromed back to its standard size, which I would prefer to do, to retain the bike’s originality. I know that I could simply (but expensively) buy a new 276 carb from Amal, but I’m trying to reuse the original parts, if at all possible. Someone who knows about carbs could also look over what I have done and maybe fix some other things too. One example is the threads on the top of the carb body are a bit worn so might be recut with the correct die?

Does anyone know anyone who could do this, based on your experience or recommendation? I will pay of course and there’s no great rush – it’ll be a few months rather than weeks before I try to start her up.

Thanks in advance for your help.
Title: Re: Are there any carb experts out there?
Post by: Bsareg on 05.08. 2019 16:25
Martin Bratbry is the chap I know of. I believe he bores out the body and sleeves the slide. Not heard of plating the body to bring it back to standard though.
Title: Re: Are there any carb experts out there?
Post by: Swarfcut on 05.08. 2019 16:39
Yes, that's the fella. Martyn or Martin Bratby. He is famous for building a twin engined Sunbeam S8. A YouTube viddy  of this machine will amaze you, and he is based in Cannock, Staffordshire, UK. Just do a Google search, his contact details come up. Restoration of carbs to better than new.
 Swarfy.
Title: Re: Are there any carb experts out there?
Post by: scotty on 05.08. 2019 16:51
Cannock, Staffs !
My old stomping ground 😁

Simon,

Sounds like the guys have some pretty good options in UK for Amal rebuilding.

Bsareg nails it regarding bored body sleeve on the slider

With your pre monobloc 276 the slide has 2 slots running up each side making a slide resleeve difficult.
I believe they would machine a new slide out of suitable material

If you still get stuck there are these guys in Seattle area who do the same
Lund Machine Company
http://www.amalsleeve.com

Their web site is educational even if you don’t use them

HTH

S
Title: Re: Are there any carb experts out there?
Post by: chaterlea25 on 06.08. 2019 00:36
Hi All,
Check out seller B561 on eBay
He makes oversize slides for AMAL and AMAC carbs along with other carb bits
Message him through one of his ebay items and he will get back to you
He has done some fantastic work on early carbs for me  *smile*

John
Title: Re: Are there any carb experts out there?
Post by: Slymo on 06.08. 2019 00:50
I did a couple of 389's myself on my Myford. I bored and sleeved them in brass and both are in regular use now. My mate has done the opposite with a 29's and 279's and 276's by lightly boring the bodies and then machining new over-sized outers for the slides. They can work really well but it tends to be a labour of love as its a lot of careful machining and a new carb isn't that expensive. The big issue with Amals of the later years is the mazac bodies with mazac slides. The wear is fast and problematic. The new hard anodized slides are a good fix and if the body isn't too bad you might just get away with that. I was very pleasantly surprised with the 376 on the Super Rocket when the new anodized slide took away about 75% of the slop.
Title: Re: Are there any carb experts out there?
Post by: dave55 on 06.08. 2019 07:49
https://www.a7a10.net/forum/index.php?topic=14116.0

See link above, recently had mine sleeved and bored at above company and very happy with his work and prices

Regards Dave
Title: Re: Are there any carb experts out there?
Post by: Simon59 on 06.08. 2019 14:33
Thanks all for your replies. Really helpful. I'll contact Martin Bratby to see if he will help me and go from there. Having said that, the Lund Machine Company in the US looks very interesting... (thanks Scotty)
Title: Re: Are there any carb experts out there?
Post by: coater87 on 06.08. 2019 17:11
 I just put a freshly sleeved 376 on the shelf, replaced by a new amal.

 If you need to change to a different slide, your screwed. Companies seem to do this differently, all with the same good end result but the parts are not interchangeable. So if you had company X sleeve your carb, you have to hope X is still in business if you need a number 3 slide or else its *work* time.

 If its not a fairy wing TT carb, I would replace it with a new perfectly working carb and keep the old one. The next caretaker can figure out what path to take with it. *dunno2*

 Lee
Title: Re: Are there any carb experts out there?
Post by: Simon59 on 07.08. 2019 12:04
Interesting response Lee. I get your point. But when you say you would replace it with a new perfectly working carb, do you mean a 276, which cost around £350 new? Or do you mean a new Monobloc or Concentric, or even another make, because there's very little room for the carb on my plunger framed A10.  *????*
Title: Re: Are there any carb experts out there?
Post by: coater87 on 07.08. 2019 15:55
Interesting response Lee. I get your point. But when you say you would replace it with a new perfectly working carb, do you mean a 276, which cost around £350 new? Or do you mean a new Monobloc or Concentric, or even another make, because there's very little room for the carb on my plunger framed A10.  *????*

I would replace it with the new 276 as originally would have been on the bike. This gives you a leg up on setting the carburetor up (initial settings are in the book), you know it fits in the envelope of the bike, you know ancillary parts like cables and choke pieces are going to fit, and the bike will run as good as it can.

 I am sure others here have used alternative carburetors, and made them work fine. But they also went through the rest of the mentioned hassles.

 I feel I wasted my money getting an older carburetor sleeved. Yes, the thing works great and no more air leaks around the slide. But, the mounting flange is/ was still warped, some of the 60 year old threads have seen better days, the float bowl cover still needed to be machined flat, the original sleeve installer has passed on, etc. etc.

 Once I purchased a new carburetor, the differences were night and day and thats how I should have went in the first place.

 Lee
Title: Re: Are there any carb experts out there?
Post by: Greybeard on 07.08. 2019 16:50
I still have the 276 on my Plungie. Bike runs pretty much as it should. I just have an occasional pop when I'm pulling away.
 
Title: Re: Are there any carb experts out there?
Post by: BigJim on 07.08. 2019 17:25
Hi GB. Did you cure the cutting out when pulling up?
Title: Re: Are there any carb experts out there?
Post by: Greybeard on 07.08. 2019 17:31
Hi GB. Did you cure the cutting out when pulling up?
Thank you for remembering, Jim.

I played with the slow running screw. I now just get an occasional pop when I open the throttle from a tick-over.
Title: Re: Are there any carb experts out there?
Post by: mikeb on 07.08. 2019 23:43
so what are the pros and cons of re-sleeving vs replacing?
i ask as my original 389 (on 61 super rocket) appears to be losing tune (getting richer) - I know its flange has been distorted (and re-flattened a coupe of times) and the slide bore is oval.
Swarfy says:
Quote
Restoration of carbs to better than new
But Slymo comments:
Quote
The big issue with Amals of the later years is the mazac bodies with mazac slides. The wear is fast and problematic.
And Lee says about re-sleeving:
Quote
If you need to change to a different slide, your screwed
Quote
I feel I wasted my money getting an older carburetor sleeved... the mounting flange is/ was still warped, some of the 60 year old threads have seen better days, the float bowl cover still needed to be machined flat, the original sleeve installer has passed on, etc. etc.

so, what to do?

side note: i did replace the very worn 289 on my b33 with a new monobloc (to save $) and while it instantly starts and runs much better i now regret not getting a new 289 due to the deeper body of the monobloc preventing using an air filter.

thanks for all views

Title: Re: Are there any carb experts out there?
Post by: Simon59 on 08.08. 2019 12:05
What indeed Mike... I could;
- leave my original carb alone, but I can feel some play in the bore and the cap threads are worn *sad2*
- Have it bored out and re-sleeved? If this works I get to keep the original carb  *smiley4*
- Buy a new 276 from Amal - for the princely sum of £350  *eek*
- Replace the 276 with a more modern model or make - but I like originality and the space available could cause cable problems *conf*

People have different views, (thanks all!) so I'm a bit confused, but I'll see what Martin Bratby says in his reply, though I hear he's very busy! 
Title: Re: Are there any carb experts out there?
Post by: clive1 on 29.11. 2019 14:46
If the threads on the carb body top are worn,
then the decision is made for you
A replacement is your solution