Amal Concentric swap 1960 GF

[SN76]

Hello guys

I Have a stock 1960 stock Golden Flash ( 6v dynamo / magneto ) with a stock Amal Monobloc 389/45 (1 1/8" ~ 28.575 mm)
How can i tell which year the Carb was produced?
I have had the bike sine 2009, it came with a newly rebuild engine and i have rebuild the Carb.  with a genuine AMAL 376 Series Monobloc Repair Kit in 2010:
Needle jet: 106
Needle: D
Main jet: 250
Pilot jet: 30cc
Throttle Slide No. 3.5 Cutaway

I have a concentric 930 that has been re-sleeved (oversize slide) and reboret and a new 932 (that i got very cheap) i would like to try to see if i would benefit from a new / less worn carburettor:

So far i have tried, 930 with:
Needle jet: 106
Needle: 4 stroke with 2 grooves
Main jet: 250 and 210
Pilot jet: without and with 25cc
Throttle Slide - No. 3 ( i only have this size for 930 and 3½ for the 932 ) What difference does the Throttle Slide have ?
It doesn't run smooth

now i have tried the new 932:
All parts are new except main jet
Needle jet: 106
Needle: 4 stroke with 2 grooves pos. 3
Main jet: 210 with air filter
Pilot jet: without
Throttle Slide - No. 3½
It runs reasonable good now but have some issues on the way to full throttle, the spark plugg  is white , i think i must try with a bigger main jet. I just have 160, 210, 250 and 260 main jet to choose from..

Which setting / jetting would you recommend for the 389/45 / 930 / 932 ?

I will use the things i have learned regarding Jetting Amal Carburettors to get my A65 to run smoothly and here i have 2 AMAL 930 carburettors.

[Greybeard]

Hi 
I'm sure you will soon get a useful reply but meanwhile will you make a post in Pictures, stories and introductions; we like to know about new members and their motorbike(s).

[Triton Thrasher]

What is wrong with the running you get with the 389?

Always fit a new needle jet on any used carburettor.

Follow the well-publicised Amal tuning procedure.

Find a main jet that is obviously too rich at full throttle and then fit progressively smaller main jets until you get good running and no sooty plugs at full throttle.

Needle clip position has a big effect on mixture at road speed throttle openings (1/4-2/3).

Slide cutaway affects mixture at small throttle openings like just off idle in traffic.

Aren't slides interchangeable between all 900 series? Concentrics use main jet about 20% smaller than a Monobloc of similar throat diameter.

[Rocket Racer]

I'd concur with the previous responses.
Anything over 30mm you're wasting your time.
 Legendary BSA tuner Eddie Dows recommendation for maximum size on a sports A10 (eg the rocket goldstar) was 1 5/32" (29.36mm) and Paul Dunstalls biggest concentric for a tuned competition 650ss norton was 30mm.
All you're doing is losing air velocity so reducing your pick up.
If you have the std 1960 carb, I'd stick with it. The concentrics were an accountants dream, made from muck metal, designed to last until the warranty expired. The mono block was a far better made carb.
Sounds like a nice bike, look forward to your intro post.
Tim

[SN76]

"What is wrong with the running you get with the 389?" I think it is worn..

"Aren't slides interchangeable between all 900 series?" My 930 has been reboret and re-sleeved (oversize slide)..

[Rocket Racer]

"What is wrong with the running you get with the 389?" I think it is worn..

"Aren't slides interchangeable between all 900 series?" My 930 have been re-sleeved..

Yes 900 series slides are interchangeable.

you can buy new monoblock slides, might be all it needs. My old ZB33 pre-monoblock I had resleeved recently after the sleeve I put in thirty years ago failed.
Personally I suggest retaining the monoblock but a lot of bikes are running mk1 concentrics if you really prefer that.
There is a thread on the forum where I posted an article on concentric low speed running. I'll see if I can find it...

http://www.a7a10.net/forum/index.php?topic=10247.0
http://www.a7a10.net/forum/index.php?topic=10243.0

[tlmark]

Interesting as my A10SR came with a concentric carb. I've only had it since august so I'm still learning all about her.
But carburetion is not spot on as it has never needed choke to start and the plugs a pretty sooty so instead of trying to guess what it needs I've ordered a new monobloc carb to fit and see how that goes.
At least I'll be able to put back to stock settings and tune from there.

[Rocket Racer]

Interesting as my A10SR came with a concentric carb. I've only had it since august so I'm still learning all about her.
But carburetion is not spot on as it has never needed choke to start and the plugs a pretty sooty so instead of trying to guess what it needs I've ordered a new monobloc carb to fit and see how that goes.
At least I'll be able to put back to stock settings and tune from there.

In context its worth considering that for literally decades monoblocks and pre monoblocks were just not available  so the budget concentric was the only (amal) option for carb replacement, so their use is prolific. We're currently quite spoilt  with not only the improved premium range of concentrics made with decent materials for the later unit BSA's, but also brand spanking monoblocks and the like. 

[BSA_54A10]

There  is absolutely nothing wrong with a concentric.
The alloy used to make them is EXACTLY the same alloy still being used on Mikuni's ( no the racing type ) Kleihns , SU, Walbro, Tilison & Webber just to name a few.
Yes they were engineered to be easy to make and yes they could have been made better but they were DESIGNED to go on bikes that got ridden every day and when fitted on a daily rider are quite fine for the job.
I would have ridden several million carby trouble free miles on mine.
What has happened is the end use is no longer what the carb was DESIGNED for and thus when fitted to TOYS that get used once every blue moon they can cause the owners grief.

The concentric design is used on nearly every modern motorcycle and funny enough most are made from the same "TRASH METAL" you are deriding.

And if you really want to find the design short commings of a monoblock, fit one to a tuned single and go for a spirited run on some really twisty roads.

Now admittadly you can do a lot more fine tuning on a monoblock than you can on a concentric as there is a bigger range of jets ,more adjustment on the needle and the bike runs far longer on the taper.

In the day IDIOT MORON MECHANICS WHO COULD NOT READ ANYTHING MORE COMPLICATED THAN A DISNEY COMIC tightened then up way too tight so they warped the flanges & ovalled the bore.
These were the same SELF PROFESSED EXPERTS WHO COULD NOT WORK OUT HOW TO ADJUST A COMICAL TWIN LEADDER and because they were the idols & heros of the day every one was quick to jump on the bandwaggon and deride these DISGUSTINGLY BAD PRODUCTS.

Funny when I can remember watching these same inferiour products hanging off A 75's doing 160 mph down Conrod Strait , then under breaking the double disc Honda fours into Pitt strait, lap after lap after lap.
I can remember Triumphs clad with concentrics and comicals being right up the clacker of riceburners & Desmo Ducattis year after year the the Castrol 6 hour till the field became too big and they axed way too many classes.

Even today the only real problem is stiction between the zinc slide & the zinc bore once the bike has been left standing for long enough for the fuel which gets adsorbed into the porus oxide layer to evaporate and not provide the lubrication that it was designed to do if the bike were ridden at least monthly.

And modern made concentrics are made from EXACTLY THE SAME ALLOY as the originals.
The only difference is anodizing the slide or the earlier brass slides.
Back in the late 60's early 70's the technology to very accurately annodize zinc did not exist.
Annodizing was tried but the slide then required machining to bring it back to round which defeated the cast to final size technology used to make the slides.

[Rocket Racer]

Trevor,
nice to see such a spirited defence of the humble concentric, a flexible and easy to tune carburetor, but one that was never fitted to pre-units.
As you mention, they are easily distorted by ham fisted owners, many have body and slide wear and the pilot jets are prone to being blocked with fuel additives. I have had concentrics on many of my bikes and still do. They are a perfectly adequate carburetor for the machines they were sold fitted to and were the carb of choice for late 60's and early 70's bikes.

If I had the choice of fitting an original fitment monoblock or a later concentric, my preference would be for the original.
Having said that on both my A10's I'm running 10TT9's, so both a factory option for the model and also period.
Personally I like to keep my bikes as sensibly period as I can: I'm currently collecting the parts to retrofit my A75 back to a comical front brake  , a PO had fitted a later disk front end. Like the concentrics, nothing wrong with a disk front brake either, but that wasnt what they ran.

Tim



 

 

[BSA_54A10]

We all have our crosses and pet peeves .
Mine is metallurgically ignorant people blaming "pot metal" for their own muitlation of a concentric.
A dear departed friend Gerry Bristow, also a metallurgist had a pet peeve with "machined from solid billet" so I carry his torch on that one out of respect for a true cyber friend.

I have done about 40,000 miles on the 626 hanging off the M20.
In that time only thing I have changed was the nylon banjo filter and the needle + jet.
However these were tune up items when new and I still consider them to be tune up items so keep a pair in the tool box.

As for disc brakes on the OIF bikes, lethal unless you fit double discs.
I can lock the A65 front wheel at 80 mph with the comicals correctly set up, nothing wrong with them, except the front end walking because of Mettans stupid wire mudguard support which does not brace the tops of the sliders.

[tlmark]

My shiny new Carb has arrived 

To polish or not to polish   

[a10 gf]

^^^ tlmark, after a period of using it, a carb review topic would be welcome, impressions, quality, results.

[a101960]

To polish or not to polish

Well, if I was you I would not bother. If you do it will certainly shine, but it is difficult to get into all the little corners and crevices once it is in situ in order to maintain that shine. Access is not great. By default for some reason Amal appear to supply all their carbs fitted with the screw in cable adjuster mixing chamber tops. A10s should have the alternative mixing chamber top fitted as described below. Otherwise it can be very difficult to get the carb on and off (this is especially true in the case of ally heads). This because there is not a lot of clearance between the top frame tube and the carb top. You might have discovered this already! The part you require is listed below.

Part Number: 389/099  Mixing Chamber Top 389 Series (To fit 2 Ferrules)

If you do go for the 389/099 top ( and I strongly advise that you do) you will need the following cables to suit:

(DOHERTY part numbers) Throttle: M42/31 inner cable length 42" outer 38"
                                         Air lever (choke) M42/38 inner cable length 42" outer 37" This assumes that you have the air lever on the handle bars. If your air lever is mounted on the frame under the seat then I do not know the part number for that item.

In both cases these cables are fitted with in line adjusters, and "top hats" to suit the mixing chamber top. What ever you do do not buy generic BSA A10 cables off of the internet because they are unlikely to fit. There is a reason I know this.

Happy carb fitting - John

[tlmark]

^^^ tlmark, after a period of using it, a carb review topic would be welcome, impressions, quality, results.

yup will do 

To polish or not to polish

Well, if I was you I would not bother. If you do it will certainly shine, but it is difficult to get into all the little corners and crevices once it is in situ in order to maintain that shine. Access is not great. By default for some reason Amal appear to supply all their carbs fitted with the screw in cable adjuster mixing chamber tops. A10s should have the alternative mixing chamber top fitted as described below. Otherwise it can be very difficult to get the carb on and off (this is especially true in the case of ally heads). This because there is not a lot of clearance between the top frame tube and the carb top. You might have discovered this already! The part you require is listed below.

Part Number: 389/099  Mixing Chamber Top 389 Series (To fit 2 Ferrules)

If you do go for the 389/099 top ( and I strongly advise that you do) you will need the following cables to suit:

(DOHERTY part numbers) Throttle: M42/31 inner cable length 42" outer 38"
                                         Air lever (choke) M42/38 inner cable length 42" outer 37" This assumes that you have the air lever on the handle bars. If your air lever is mounted on the frame under the seat then I do not know the part number for that item.

In both cases these cables are fitted with in line adjusters, and "top hats" to suit the mixing chamber top. What ever you do do not buy generic BSA A10 cables off of the internet because they are unlikely to fit. There is a reason I know this.

Happy carb fitting - John

Thanks John I'll bear that in mind

I'll probably fit this after I've pulled the head over winter. as I also want to have a go at fixing a oil leak on the primary drive case over winter.

So a list of jobs and mods to do