Twin carb head

[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?

[Housewiz]

Muskrat - are those manifolds from Dyno Dave or another source?  Also curious how the fabricator arrived at the manifold length.

Thanks,

Steve

[muskrat]

G'day Steve,
                 original maifolds were 1 5/8" I made mine 1 1/2" for a little more top end with the 357 cam. Mine started with a flange both ends then when I changed to Kehins I cut the flange off and use a rubber hose, similat to RR's pic above.
Cheers

[Housewiz]

Muskrat,

I am leaning towards a pair of 276 Amals for my twin carb head - throat dia to be determined and hopefully matched to the head inlets and manifolds.  It really looks a bit dimensionally tight in the carb arena of an A10.  I wonder if a slightly angled manifold tube or a shaved base flange would put the carbs just out of each other's way and out of the way of the bike frame?

Thanks,

Steve

[Rocket Racer]

Muskrat,

I am leaning towards a pair of 276 Amals for my twin carb head - throat dia to be determined and hopefully matched to the head inlets and manifolds.  It really looks a bit dimensionally tight in the carb arena of an A10.  I wonder if a slightly angled manifold tube or a shaved base flange would put the carbs just out of each other's way and out of the way of the bike frame?

Thanks,

Steve

Steve,
 you will want a left and right sided carb pairing, even a chopped monblock for that matter. The 276 wasnt considered a performance carb in its day and wouldnt have been original fitment either.
I was lucky enough to source 10TT9's (and they do touch each other), they certainly look lovely and in a straight line work very well, but then I suffer from the usual sidecar issues of carb swill on corners which solo riders don't need to worry about. Am considering adding a 3rd matchbox float to address...
My rigid frame has a frame tube right by the carbs but they still sit side by side and parrallel. Personally I think they dont look as good when kicked out at an angle, but thats purely a personal asthetic view.
Issue with 276's is that they will either be worn or expensive, not sure why that path would appeal. If I couldnt have found a 2nd matching 10TT9, I'd have fitted concentrics for ease of tuning and cheaper parts.
Look forward to seeing what you do.

Tim

[Housewiz]

Hey Tim,

Definitely going for a little bling with a set of L & R 276'ers.  Hopefully I can source a nice pair.  As long as they idle, don't hesitate when street racing a Harley, run well at all throttle openings, and don't leak all over, I will be happy.

The few photos I have seen they appear to touch either the frame or each other - don't want that to happen.

Sidecar racing - very cool.  For the last two years, I have been restoring 40 year-old electric garden tractors - time to go fast and make a little noise.  www.watts-up-elec-traks.com

Thanks,

Steve

[muskrat]

 " As long as they idle, don't hesitate when street racing a Harley, run well at all throttle openings, and don't leak all over, I will be happy."
Sad, Sad Steve, just kidding. For about $700 for a nice new pair. http://www.amalcarb.co.uk/ProductSearchResults.aspx?SearchTerm=276#
Cheers

[Housewiz]

Hey Muskrat,

Just sold one of my restored 40 year-old electric garden tractors (www.watts-up-elec-traks.com) to support my new & quite costly A10 habit so those carbs now have a financial backer. 

I saw them a couple days ago on the Amal site - wouldn't a matched R & L set look great on a SR??  Float bowls on the outside of course!  Perfect compliment to a twin carb head.  I appreciate your email and fellow interest in stuff that I think is cool and a step or two off the beaten path.  I like the Apple company logo - " Think Different".

Thanks,

Steve

[Housewiz]

LJ,

That ad is the exact look/install I am after.  Those carbs, w/the adjacent float bowl, to me at least, are the best looking set-up going.

Muskrat,

Those manifold tubes look longer than the factory manifolds.  Did your porting and 30mm carbs dictate that dimension?

Thanks,

Steve

[muskrat]

 Originally I had 2 x 32mm concentrics on the A7SS racer feeding methanol bolted to the head with a 1/4" alloy plate/manifold. Now on the road as a A10 detuned to 30mm Kehins I found about 1 1/2" just about right, but I'm still a rev head.
Cheers

[Boomer]

Newbie to this forum, thought I would post a shot of my '63 RGS with a twin carb set-up. Bike has been sitting since '71 and it took me 17 years to convince the original owner to part with his bike. He said the shop he bought the bike from new gave him the head set-up when they rebuilt his engine, w/carbs and manifolds, and was told it came off a factory racer. Manifolds are different then speed equipment supplied on BSA sales sheet that Trevinoz posted. Hope to get it going for the 2014 BSA rally in NorCal. It's a documented RGS with Dunlop alloy rims, ARRT stamped gearbox, and RGS gauge mounts and gauges. It's my understanding that the early heads with the manifold had the casting part number of 67-1102 and the later twin carb heads had 67-1106.

Bike as found:


http://i1084.photobucket.com/albums/j414/goldsparky62/RocketGS001-1.jpg

http://i1084.photobucket.com/albums/j414/goldsparky62/RocketGS002-1.jpg

[muskrat]

G'day Boomer, welcome to the forum.
The 1102 is the A7 head, the 1106 is the A10. She doesn't look like too much work/parts to get mobile. Give us an intro in Bikes, Pictures & Members.
All the help and info is just a mouse click away.
Cheers