The BSA A7-A10 Forum

Technical => Amal, Carburation => Topic started by: BigJim on 08.05. 2019 18:16

Title: Concentric set up
Post by: BigJim on 08.05. 2019 18:16
All opinions entertained.
Looking to get a new concentric for bike, bored with replacing bits and still problematic.
Bike is an iron head swing arm A10, anyone got similar with concentric and what set up works best for them?
Have a basic kandn filter[no card, looks like fine wire].
run on 97 ron fuel and 7.25 comp if that relevant?
Title: Re: Concentric set up
Post by: morris on 08.05. 2019 21:56
If it can be of any help, my ‘52 plunger came with a 928 concentric;
20 pilot
3 1/2 slide
106 needle jet
250 main jet
But why not get a mono-bloc as per original?
Got one on the ‘58 SA bought from Burlen/Amal a couple of years ago and it’s performing really well. It’s a 389/45 with the same setup as the plunger’s concentric except for the pilot which is a 25
Title: Re: Concentric set up
Post by: BigJim on 08.05. 2019 22:52
Thank you morris for the data.
  Have an old mono which i spent many an hour trying to stop leaking. I imagine the new jobbie would be fine with no bodgery of cackhanded owner [me] but wonder if longterm sidestand park may get it leaking? However i could be tempted if the distance to frame from top is greater to give a better clearance for cable routing. Will dig my old one out and compare. Also think an earlier carb was used originally on 55 A10.
Title: Re: Concentric set up
Post by: beezermacc on 09.05. 2019 09:47
The pre '60 A10 swinging arm, had a 376 carb with 1.1/16 inlet, the 1960 onwards A10 had a 389 with 1.1/8 inlet. Before buying a carb check the inlet size on your cylinder head. Even though the cylinder head part number changes in 1960 the vast majority of cylinder heads carry the same part number regardless of inlet tract size.
Title: Re: Concentric set up
Post by: morris on 09.05. 2019 17:10
For the record, should have mentioned that my ‘58 SA has a ‘62 engine with a 1 1/8 inlet.
I leave it regularly on the side stand for a couple of hours. No leaks too report.
Only noticeable difference is that when tickling the monobloc leaves a stinky finger while the concentric don’t. 
Title: Re: Concentric set up
Post by: RDfella on 09.05. 2019 18:12
Most of my bikes have had / have monoblocs. Far better carb in my view than a concentric - and never known one leak (apart from one with a stubborn float which stuck if left for any length of time with fuel bowl empty. Hopefully now cured by trimming float).
Title: Re: Concentric set up
Post by: Swarfcut on 09.05. 2019 20:12
My only problem ever with a Monobloc, a long, long time ago, was  to replace the worn threaded idle adjustment screw with a new one, which  seized and then sheared off when I attempted to adjust it a few months later. Brass and Aluminium like to hold hands, so now I put a dab of silicone grease on similar threads, seems to work.   Proved impossible to drill out, so be aware if buying a used item. You can bet my experience is not unique.