Twin carb head - which Amal's should be used?

[Housewiz]

Might have found a twin carb head.  1102 is the stamped #.  Is this the A7 option head or the A10?  Does anyone have an opinion if it will bolt up to SR barrels?  If it does, and I bring it home, what Amals should I start looking for?  Stock single carb throat on the 376 is 1- 1/16".  I would think smaller throat carbs would be best and if that's the case, what vintage R & L Amals would complete the Holy Grail quest?

As always, thanks for chiming in and setting me straight!

Steve

[trevinoz]

Steve,
                 That would be an A7 head.
It will fit the S.R. but the compression will be a bit high due to the smaller combustion chamber. Would need to be modified.
You would need adapters to fit twin carbies.
Monoblocs were made in both R.H & L.H. versions from about 1965/66 but only in 389/689 versions, the smallest being 1-1/8".
Concentrics should be the easiest way to go.
   Trev.

[Housewiz]

Hey Trev,

Thanks for the lightening reply.  Is there any room in your backyard to pitch a tent so I can pick your brain for a couple of weeks?  Kidding course - I'm in the US.

OK, so back to the head modification.  That means moderate metal removal in the combustion chamber with new valve seats, guides, etc?  7.5 to 8.0 CR is all would want/need.  Due to the fairly straight shot of air/fuel from the dual carbs, would porting be necessary?  Do you have a throat size in mind for the concentrics?  I was hoping to stick with monoblocs to retain the 50's vintage look.

Steve

[Rgs-Bill]

Steve you need to sign on to Myles Raymond's TWIN CARB MYSTERY web site.  Amal did make a left and a right for the twin carb manifolds.  The right is a 389, the left one is a 600 something or other. Amal also made a chopped carb, I am not quite sure how that one was used. Amal is now  making carbs again, just type in  (Amal carb site U K ) .  The twin carb A-7 head will not fit the A-10 without modifications.  Dyno Dave is now making an alloy re-pop of the cast iron double manifolds for these heads.  Dyno Dave also has info on these heads. They had to offer these dual carb heads to the public  (so many had to be in   production) so they could qualify to run this head at Daytona on their race bikes, it had to be a normal production cylinder head so the bikes at Daytona raceway could run the heads also.  Hope this helps you.      danielboss@juno.com      also has some info on these heads.  The last one I saw go on FLEA BAY for $1400. us funds.

[Fast 58 BSA]

Hello Housewiz,

I have a 1106 twin carb head that I am restoring for my GF Cafe. I will be running a matched pair 389/689, 1 1/8" Monoblocs. There is a thread on the topic, my concern was that they might be too big, but feedback from others on the forum is that it should work. I will leave original valve size for good flow

Best,
Carl

[Housewiz]

Trev thinks the head will fit, RGS Bill thinks not.  Have either of you guys tried or know someone that has and what was the result?

Thanks guys,

Steve

[whittakers]

We have a twin carb head A7SS on the race outfit. Straightforward to fit, put largest valves in we could using the existing seats and had to relieve a small amount around the edge of the combustion chamber (as A7 is smaller than A10) - didn't have to take much out. Ended up with another 0.5 : 1 compression ratio. Regarding carbs, with straight manifolds they do fit - just. I have a LH Monobloc on left pot and a (homemade) chopped LH Monobloc on the right pot. Access to the idle and mixture screws is challenging but not imposible. The only real problem is that the throttle cables exit the carbs very close to the tank, I removed the carb top adjuster and opened out the carb top for the ferrule to sit in properly.
We are using 1" 5/32 carbs (its what we had) and are possibly a little too large for road use - though fab on the track. Jet sizes, we started with single carb sizes except mains (memory reckons that single carb was 420 ish, twins started with 280 ish).
Is it worth doing? On the dyno with a single carb it was struggling to breath over 5600rpm, with twin carbs it delivers well past 6800 rpm and floats the valves.
Mark

[Rgs-Bill]

 I believe the alloy dual carb heads had 1 and 1/2 inch intake valves, which lets the motor breath better.  The Iron head dual carbys had smaller intakes I believe.  Talk to Myles Raymond across the pond, he also has a web site for the very rare Super Flash BSA  1953 & 1954, only 700 and a few of these were made. They had the same motor ( fore runner ) to the later Super Rocket motors and Rocket Gold Star motors, which were all stamped HHC below the serial #.  I believe the only differences were the Intake valve size ( smaller )  and no 67-357 full race  cam shaft, had a 67-356 cam.  
     danielboss@juno.com   races these I believe, and Dyno Dave also.  Dyno Dave makes a really nice alloy after market dual bolt on intakes, for around 100 bucks for these manifolds.

adm edit: please do not change tirle in an ongoing thread, post a new topic if needed. Thanks.

[muskrat]

 G'day Steve. I had an A7 twin carb head on my '57 A7SS racer running twin 932's on methanol so jetting will be way off. The head is now on the cafe (same bike just upsized to A10) running twin 30mm Kehin's. So for yours I'd run twin 930 concentrics 30 pilot, 3 - 3 1/2 slide, 106 needle jet, middle notch needle, 190 mains. Open up the circumfrence of the combustion chamber to match the bore and use A10 SR valves (1.41" and 1.37" I think). Can use the original seats with a regrind.
Cheers

[Housewiz]

RGS Bill,

I am on Dyno Dave's waiting list for maifolds and have corresponded with Daniel Boss and checked out his fan website.

Muscrat,

Does the combustion chamber, after matching the SR barrel bore, have to be enlarged as well due to the smaller A7 chamber creating a too high compression ratio?

Thanks guys,

Steve

[muskrat]

G'day Sreve, that's all I did. The cr would only be a poofteenth higher so good to run 8 to 8.5 : 1 pistons.
Cheers

[duTch]

  I saw a picture somewhere of what I think was a 689, the 389 left version, but with a 'cut-down' float bowl,and the idle/mixture screws on the outside, made to fit in ok, but can't remember where I saw it..?

 RGS Bill, I'm no authority, but was told the other day, by someone who I have good reason to believe knows, that only 523 Super Flashes were made.
  Not to be taken as gospel, nor to be taken 'off topic'

 cheers, duTch