The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Amal, Carburation, Fuel => Topic started by: Drew Back on 06.08. 2014 15:10
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Getting my motor back together went to put carb on(amal 389) and realized it wont fit..I know the 276 is what is supposed to be on there now but they are pretty costly, new around $600 was thinking about mikuni but what exact model would I need and will stock throttle cable work..I dont have the stock air filter was planning to run velocity stack..I just want something that is going to be dependable and run well,I do see some used 276 carbs for under $200 but I dont and cant assume condition for the price..
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If you don't care about original looks, the Amal Concentric Mk 1 is about the smallest, cheapest simplest carburettor.
Don't get a carb with a significantly bigger bore than original, if you want a bike that runs properly.
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G'day Drew.
Have you fitted an alloy head? As TT says a concentric will fit on a iron head plunger A10 but not an alloy head due to the intake angle.
Cheers
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No it is just the standard cast iron head nothing fancy just a bummer about that 389 goes to show you can never have enough spare parts..
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Why doesn't the 389 fit?
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The carb is to tall could never get cable in top and no clearance at rear for air cleaner/velocity stack and it sits way to close to oil bag..
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Unfortunately the carby is a bit of a problem on the plunger models. The concentric is the easiest swap for the original 276 and even then the best you can do is a bellmouth.
You can fit a 376 Monobloc but it is a squeeze, I have one on my plunger A10.
No way would you ever get a 389 on plus they are too big in bore size anyway.
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I have a 1954 A10 Plunger and the concentric carb won't fit because the engine is larger dimension than the earlier engine. A friend has a 1953 plunger and the barrel and the head are smaller in diameter.
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I managed to fit a 389 to my alloy head plunger, but only after truncating the top cover, and the cable was a bit ugly.
No way could fit a decent filter, though I did try some weird shapes.
Finally decided on the extended offset inlet tract so now can run a K&N type filter, and works ok, but also had to relocate the battery.
Vitto, I guess your mate has the small fin barrels, and yours are big fin...?? Can't comment on that as not sure of sm/f dimensions
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That is good to know I am running the thick flange jug so I guess I have to save my pennies for that new 276 carb that cost is a little less than I payed for the whole bike..OUCH!!!!!!
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Well I helped a friend mount a pre-monoblock today and no way were the cables and adjusters for slide and choke going to clear the top tube. We had to ditch the choke altogether and counter bore the top of the carb for a low slung tophat fitting to take slide cable to make it work. Admittedly it is a swinging arm topend but I measured both an old plunger head and the manifold seems to be the same length??(https://www.a7a10.net/forum/proxy.php?request=http%3A%2F%2Fi244.photobucket.com%2Falbums%2Fgg3%2Ftakka22%2F003_zps880ea6c0.jpg&hash=78a9f38f4744ebd1431b21535621bea0d94643b8) (http://s244.photobucket.com/user/takka22/media/003_zps880ea6c0.jpg.html)?
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I have a 1954 A10 Plunger and the concentric carb won't fit because the engine is larger dimension than the earlier engine. A friend has a 1953 plunger and the barrel and the head are smaller in diameter.
hi thats weird as i have a 55 plunger with 626 concentric on and it fits ok bit tight at top with cables but starts really easily first or second kick even after laying up over winter. Just bought new 276 for originality from burlen and hoping it wont affect this aspect of the bike ....... famous last words eh!! 😕
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On this subject, would anyone be kind enough to list the settings/jets/slide they have had success with using a 626 Mk 1 Concentric on a plunger A10 (a '52 I think)?
I ask because I have just been asked (as if I would know!) by a friend who's rebuilding a basket case which has come with a concentric that allegedly 'worked fine' (don't they all). But the burnt exhaust valves suggest otherwise and the new owner is rightly concerned.
Thanks muchly in advance.
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The settings/jets/slide etc for a plunger A7 would also be much appreciated.
cheers
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G'day olev. Doubt if my settings will do. 1951 A7 plunger. I run a 932 with no airfilter and straight through pipes (the mufflers are empty) on mine *eek*. 30 pilot, screw 1 turn out, #4 slide, .106 needle jet, needle bottom clip, 300 main. A7SS head with A10 valves and 357 cam. *bash*.
Cheers
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Thanks Musky,
You're right, those settings are a little off what I expected.
straight through pipes?? i'm scandalised. don't you have coppers in NSW.
how do you sleep at night?
cheers,
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I read this post with interest, as I have a 1957 plunger and I have been playing about with the carb and head, firstly the intake on a swinging arm head is tilted and does not allow the fitting of some carbs and because I could not get a head for my bike I used an Ariel Huntmaster head which is almost the same as the early A10 heads, with a short intake for the carb and horizontal, I am running a Amal concentric R928 using a 106 needle jet and a 230 main jet, it seems to go quite well but it seems quite juicy with the petrol, do you think I should try a smaller main jet.
BTW, I did actually manage to saw the intake manifold from a S/A head vertical so that the carb would just fit in but the screws had to be in at an angle which made it a little difficult but it ran okay.
Kind regards TTJohn
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G'day John.
First thing I'd do is check the fuel height. You will need to make level tube. Get a float bowl drain plug, drill and tap 1/8" BSP, screw in a hose tail, attach clear tube and bring up to the top of the carb. Turn the fuel on and see the level in the tube. A 928 should have a fuel height between 0.17" (rich) to 0.24" (lean) below the bowl/body joint.
Cheers
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Muskrat.
Thanks for the advise but my carb is level and there does not appear to be any way to alter the level in it, plastic float.
I have been playing about with the jetting today and have reduced the size of the main jet from 230 to 140, I know it seems quite drastic but I thought I'd give it a go and after a bit of fine tuning with the mixture control and air intake, it still seems to go okay and hopefully it will be a bit more economical.
TTJohn
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Hey John, slight difference, but I'm running a Monobloc on an alloy head, with a 25 pilot/105needle/ 240 main and when I changed to a 105 needle jet, it made a lot of difference...!
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G'day John.
First I'd throw away the plastic float and invest in a stay up float (adjustable) and viton tipped needle. A level carb is a cinch to get right but on a downdraft like pictured (alloy heads) can be a fight.
As duTch suggests the needle jet and needle are subject to wear. A new pair could make all the difference.
Remember most of your riding is on the slide and needle jet (1/4 to 1/2 throttle). Spirited riding is on the needle clip and main jet. A colour tune and plug chops is the best way to get it right. I always err on the rich side.
My A7 plunger gives 60 mpg, my A10 cafe (read racer) gives 40 mpg, my 1100 Honda is lucky to give 25 mpg *eek* but fun doing it *whistle*.
Cheers
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Hello John
For what it's worth the 928 on my Flash has a 20 pilot, no. 3 slide, 106 needle and 240 main, needle in middle position. Reckon it gives a decent mixture through the normal range (with a question over main jet as I rarely if ever use top end throttle, where it matters most). And 60 mpg or more. What sort of mpg do you reckon you are getting? If it is very low I would agree that the float fuel level is most likely culprit. It can be lowered by tapping the brass insert where needle sits from the upper side to lean up the mixture, and this makes a big difference in running. Also agree that a viton needle is pretty much essential. The 'stay up' MoD type float is easier to adjust, but the hollow plastic ones are perfectly ethanol proof, but could of course leak if damaged.
cheers,
Mike