Twin carb head

[olev]

He's back..... and a hundred bucks cheeper.

http://cgi.ebay.com.au/BSA-ROAD-SUPER-ROCKET-GOLDSTAR-A10-AL-HEAD_W0QQitemZ190341971661QQcmdZViewItemQQptZAU_Motorcycle_Parts_Accessories?hash=item2c5143fecd&_trksid=p3286.c0.m14

I bought a toolbox off this bloke a while back. It was no bargain but I'm happy.

Trevor,
do you think it might be Arthur starting to unload?? maybe his ceiling has collapsed.
cheers

[trevinoz]

Olev,
             It's not Arthur. I have bought a couple of bits off this bloke also, his name is Ian.
Funny thing about old Arthur, he contacted a mate recently trying to get some bits and pieces. God knows why as he has enough in his shed to keep a team of restorers going for a lifetime.
If he just sold his pile of alloy heads he could live comfortably.
Trev.

[rocket man]

some people are horders and dont like letting stuff go

[GuyboA10]

G'day, i've dealt with Arthur b4 and i would NEVER do it again!! He is a prick. I think he is short a few screws in his head, but not in his shed, apparently. cheers, Guybo.

[bl**dydrivers]

there was a twin carb head on ebay.co.uk that went for 155.00 had the manifold included, might have required some work but gosh what a bargain.

[old53]

Ive never really understood how fitting twin carbs improves performance (although im sure it does).On a single carb engine ,once every revolution, one of the cylinders takes its turn to draw in fuel/air mixture through the carb.On a twin carb engine each clylinder breathes through its own carb every other rev which is the same thing.So why is that better?
  I could understand if both cylinders were trying to draw mixture through the carb at the same time.But they dont.
  I can only think that on the twin carb the inlet tract takes a more direct and less convoluted  path  than on the single so its streamlining the flow.Is that it?
Mike

Hello  just logged on to this forum and like Mike I am wondering if there is any statistical/performance facts  on how much improvement fitting twin carbs to A10 achieves. -Carey

[manosound]

Carey,

I know jack about twin-carb heads, but I can detect when a new member is trying to enter the forum  discretely and without a lot of fuss. So let me support that effort by saying,



"HEY, CAREY, WELCOME TO THE FORUM!!! GLAD YOU COULD JOIN US! I LIKE THE LOOK OF YOUR BIKE AND HOPE TO SEE MORE PICTURES SOON."  

Richard L.

[muskrat]

G'day Carey,
                 ditto to Richard L's post, welcome.
Twin carbs do work better. I picked up 10 seconds a lap at Eastern Creek after fitting '54 A7 "twin carb" head to my '57 A7SS. Look at most performance motors, past and present, they have a carb and pipe for each cylinder.
Cheers

[Lightningpower]

What size do you think those monoblocs would be?

[Rocket Racer]

surprising to see the 276 pre monobloc carbs on a 1956 - 60 twin port head!

They would be TT racing carbs rather than humble 276 or 289 carbies

[Big Nick]

I have 67-1102 head with twin stubs, i have had it running on my A10 before ( they were A7 sized ) i keep on thinking about have it taken out to A10 size to get more power. any thoughts ?

[Rocket Racer]

I have 67-1102 head with twin stubs, i have had it running on my A10 before ( they were A7 sized ) i keep on thinking about have it taken out to A10 size to get more power. any thoughts ?

My 500 head had been modified by a previous owner to A10 radius bores and taken out to 30mm in the ports but was still 500 small valved. I took it out to late A10 big valves inlet and exhaust and had the porting improved, but am currently having to down size the exhaust valve size again at great expense as I have had issues with one of the exhaust valves clipping (this engine is running 357 cam and pulling to 7500).
Depending on your use I would suggest just changing to larger inlet valves and keeping the porting the standard A10 diameter (27mm) to retain gas velocity.

Small valves and ports provide a nice motor but bigger valves and ports will allow more top end if thats what your after. My 30mm ports and TT carbs seem to pull well enough. It sailed through to 7500 when I wasnt paying enough attention, I try and keep it to 7200 or below. Not sure how it compares down low but its keeping up with some much bigger bikes out on the track

[Triton Thrasher]

They would be TT racing carbs rather than humble 276 or 289 carbies

Regarding your attached pic:

I'm doing something similar with stubs and radiator hose on my Triton.  What are the contours inside your inlets like?  Do they step to larger diameter from stub to hose and back in again at the head?

[Rocket Racer]

In essence my carb & head stubs effectively touch and the hose/hose clamps simply provide an easy way of clamping the two together.
Stock stubs are available for later triumphs and so are (plastic?) connectors that have a ridge so that the stubs dont connect (so better isolates the vibration) but in my case the ports on the heads are no where near aligned with the head studs, so we had to make bespoke stubs & did all four. There may be a notional mm between the stubs but they are pushed hard against each other then the hose clamps done up.
I'm using a high quality marine hose with a wire weave. Make removing the carbs a breeze trackside.
 My stubs carry the diameter of the head port as it was already 30mm. I havent got too worried about matching ports and stubs exactly reasoning a bit of turbulence is not a bad thing.

I dont know what if any difference the carbs make, but certainly a pair of pukka race TT's are a lovely bit of bling compared to a muck metal 930

They would be TT racing carbs rather than humble 276 or 289 carbies

Regarding your attached pic:

I'm doing something similar with stubs and radiator hose on my Triton.  What are the contours inside your inlets like?  Do they step to larger diameter from stub to hose and back in again at the head?