Amal Carb Types: Concentric and ?

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Hi everyone, im still rebuilding my 1970 roadster and it currently has a single mikuni on it and i want to put it back to the original twin carby setup, i was talking to someone on the weekend and i told him i wanted to put the twin carb setup back on like original and he thought that the early commandos didnt have the 'concentric' carb, he was sure it was another type, any one know for sure?

Thanks
Adam
 
interstateOz said:
Is it possibly the MKII Amal? it does look slightly different and i think that is what he called it?

No standard Commando model ever had MkII Concentrics, as production ended before the MkII carb became available, as far as I know.
 
Nortons up to 1966 were fitted with monoblocs, 67 and later were fitted with concentric mk1- 30mm till 71 32mm 72 and later.
Al
 
The only exception that I've ever seen is that factory Production Racers had Amal GPs for a year or so.

Oh...and some of AMC's James Commandos had Monoblocs :)

A road-going Norton Commando would certainly have left the factory with Concentrics.
 
possm said:
Nortons up to 1966 were fitted with monoblocs, 67 and later were fitted with concentric mk1- 30mm till 71 32mm 72 and later.
Al

Thanks possm, thats what i needed to know so 30mm on the 1970 models then.

Is there much difference in power with a 30mm V's 32mm if appropriate boring to manifold/intake is done?
 
Small ports normally give better torque with a little loss at the top i doubt it would be noticeable unless the rest or the motor was built to suit i.e cam compression etc.. in the mid 70's i brought a 1971 drum brake ex police commando and boy was that bike a flyer, i sold it to a mate and brought a 850 but that 750 was still at the front of the pack.
 
+1 another yellow fellow
The japenese copied the brits w/ the cb series.
Everybody wanted to be that brit roadster.
Then in 1974-75 the commando started resembling the other commuter bikes.
I love my 72 it comes with a built in coolness option and the firey attitude of a red head :mrgreen:
Oh and I'm 32mm gravity injested 10:1 indigestion w/ sparks coming off the rear tire :shock:
Thee Marshal (uncompensated poet)
 
Marshall,
What! Are you trying to compete with hobot?

Dave 69S
 
Marshall has identical words as me to describe our opinion of Combat cream of the crop. He's just teasing about rear tire sparks, he really means sparks from leaning.
I have gone back and froth between single 34 Mukuni and dual 32 Concentrics, expect for the lighter throttle of single carb I prefer the smaller throat Amals for crispher response but lost 10 mph on top end if I waited to max out WOT.
125 mph vs 135. I had to twist grip further on 34 single to get similar get up as Amals. In the end a factory Combat will be my last ride as the most all around
delightful, easy to operate and spunky enough to keep me pleased.
If you are not going for redline WOT top end performance I discourage a big single.
I've two single carb left overs, one I bought and another that came on Trixie but
switched out for Peels Amal that would be able to keep up with her new engine.
 
Hey Dave,
Hobot has it covered pretty well.
I was just substituting for the day :shock:
Still combat rules :mrgreen:
Great rebuild pics by the way
thanks,
Marshal
 
MarshalNorton said:
Hey Dave,
Hobot has it covered pretty well.
I was just substituting for the day :shock:
Still combat rules :mrgreen:
Great rebuild pics by the way
thanks,
Marshal
 
illf8ed said:
MarshalNorton said:
Hey Dave,
Hobot has it covered pretty well.
I was just substituting for the day :shock:
Still combat rules :mrgreen:
Great rebuild pics by the way
thanks,
Marshal

I think the enter key has a hair trigger...posted before I could type anything. Wanted to add 2 cents. Just another happy combat owner closing on 50,000 miles on the odometer and still running strong :)
 
Took me most a decade to cover most variations of 750 engine set ups.
Peels best combo by far was the 28 mm head with 10 CR and 2S cam and 1.5" pipes made into a 2>1>empty Dunstall megaphone with his soup can baffle replaced byan end plate with 1 3/4" hole blown through. First run with 34 single and Boyer, for run out form under response. I left the small 28 mm head lip untouched but further interfered with but crude intruding rubber-fiber material. Its was accidental set up waiting for real Combat head to get done. When I put dual Amals on I had to be more careful on throttle not to just spin on Gravel noticed-appreciated less wrist action to reach speed, pass and satisfy desire to zoom into turns.

Similar happened when I returned factory Trixie Combat to dual Amals, more ease of operation with better throttle response and spunk. Looks nicer too.
Top end can use as much carb as possible but real life get up and go to almost as fast top end, smaller works nicer. Its not a night and day difference though, you do have to twist throttle a good bit to feel the differences. If pure ease of operation and maintenance in maturing wiser man riding and lower wrist effort then single is better deal but for appearances.
 
I honestly do not understand how a single 34mm Mikuni with a little over half the intake area of two 32mm Amals can give roughly the same performance. I understand how to get enough gas into the engine, but how can you get enough air through the restricted space. I would think a 40mm or so would be needed, but most of the posts I have read in this forum seem to report poor performance from larger single carbs.

If someone wishes to answer, assume you are talking to a child in the 8th grade.............who will have to take pre algebra next year. Numbers are ok, but the only symbols I want to see are the little faces.
 
Diablouph said:
I honestly do not understand how a single 34mm Mikuni with a little over half the intake area of two 32mm Amals can give roughly the same performance.

In a 360 degree crank vertical twin 4 stroke engine, only one of its two cylinders will be on the induction stroke at any particular moment, so theoretically at least, as I understand it, the single carb only needs to be large enough to feed one cylinder at a time, although I believe there are some losses due to the airflow constantly having to change direction between cylinders and a bifurcated manifold isn't perhaps an ideal shape for the inlet passage, so a single carb can "run out of breath" at high RPM which a slightly bigger carb may help to compensate for.
 
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