Needing Air

This final prototype variant is designed for cut-out spray nozzles and brass throttle slides. The tooled components can flow flat-top and cut-out nozzles equally well and can match brass and alloy slide profiles. Simple retrofit is possible or as part of the full suite of phase 1 mods. Interested?
Ta.

Certainly be interested to hear how they perform.

The slides in the little Villiers carbs are solid (plated brass), with just an ole for the needle.
Apart from the weight, I always wondered how something like that would perform in an Amal.

Its (just) possible the hollow ones may have some sort of vortex that improves the fuel mixture/distribution,
so it will be interesting...

Rohan said:

Certainly be interested to hear how they perform.

The slides in the little Villiers carbs are solid (plated brass), with just an ole for the needle.
Apart from the weight, I always wondered how something like that would perform in an Amal.

Its (just) possible the hollow ones may have some sort of vortex that improves the fuel mixture/distribution,
so it will be interesting...

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Norton Commandos were fitted with AMAL Concentric Mark 1s as standard equipment. The mods are developmental improvements to Mark 1s.
Ta.

Yes, we realise that.
Tell us how they work though.....

And for Ludwig, from a previous thread here.

L.A.B. said:

According to the account given by Norton development tester Bob Rowley in Mick Duckworth's book 'Norton Commando' the Amal modification cured: "the 850's flat spot under sudden acceleration" <snippo>

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Rohan said:

And for Ludwig, from a previous thread here.

L.A.B. said:

According to the account given by Norton development tester Bob Rowley in Mick Duckworth's book 'Norton Commando' the Amal modification cured: "the 850's flat spot under sudden acceleration" <snippo>

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Well , just like I said :
" I red somewhere .."

Why not a link to that thread :
jetting-932-amals-850-comando-t19424.html?hilit=spray%20tube
It is full of : " I red .. I believe .. I think .. someone said ..according to .." etc ..
Nothing but hearsay and contradicting statements .
I am still waiting for a final answer from John Healey .
( not that I'm holding my breath .)

At least Needing here is doing some experiments to separate facts from fantasy .
Rohan , maybe you could do some testing yourself with different types of spraytubes an provide us with some real answers ? ;
I woud be happy to hear the results ..

Hi ludwig.
Re: that link re stepped spray nozzles - I'm glad I missed it.
Ta.
I will draw some pictures tomorrow to explain the function of the flow disc in conjunction with the spray nozzle. The transitions through throttle openings are the critical aspects of how it all functions.
Ta.

It's like the UFO, except it's different.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1149364740

Triton Thrasher said:

It's like the UFO, except it's different.

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Like AMALs are like Mikunis, except they're different. My focus is the lower throttle opening transitions but WOT may also be enhanced by airspace reduction (re UFO) and channelling (re my design). Dyno runs to assess brass slide variant from 1000 to 7000rpm on Wednesday.
Ta.

Ludwig, my 850s have all had stepped spray tubes, no flat spot off idle.
Problem solved !
There is lots in print when you hunt around on this too.
Some of it from 40+ years ago....

We will have to put you into the 'doubting thomas' category on this.

Perhaps not the instant puff of black smoke that the guzzi with Dell Orto pumpers has,
but that thing gets woeful fuel mileage if you twist the throttle a lot.
Dell Ortos also have a reputation for being more tempermental than even Amals,
i (fondly ?) recall feeling a cold foot when fuel p'd out the overflow, more than once....

Rohan said:

Ludwig, my 850s have all had stepped spray tubes, no flat spot off idle.
Problem solved !
There is lots in print when you hunt around on this too.
Some of it from 40+ years ago....

We will have to put you into the 'doubting thomas' category on this.

Perhaps not the instant puff of black smoke that the guzzi with Dell Orto pumpers has,
but that thing gets woeful fuel mileage if you twist the throttle a lot.
Dell Ortos also have a reputation for being more tempermental than even Amals,
i (fondly ?) recall feeling a cold foot when fuel p'd out the overflow, more than once....

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Hi rohan.
The discussion of the history of stepped spray nozzles is simple obfuscation and another distraction (you're cutting into next months quota). Stepped spray nozzles in the 21st century are simply another tuning option available to AMAL carby users.
"Dell Ortos on my Commando" may be the original thread concept I encourage you to initiate. Perhaps have a go at throttle pumped AMALs as an original thought - oh no, too late, I just thought that thought!
When you say "...We..." in your posts, perhaps you could disclose just how many voices do actually muttter away in there.
Ta.

I believe its just the shorter-lower path for fuel to rise before spilling into air stream more than venturi sucktion on poor low rpm sucktion engines like 2smokes and 850s. A V groove by hand file works for me but a step cut out may be easier for production. Might see what happens w/o spray tubes installed as me bump up both off idle spunk and more mixture flow w/o the obstruction. May lower mileage but can have everything all the time.

hobot said:

on poor low rpm sucktion engines like 2smokes

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2 strokes don't have poor low suction ?
Thats why 2 stroke and 4 stroke amals differ....

needing said:

[

The discussion of the history of stepped spray nozzles is simple obfuscation and another distraction (you're cutting into next months quota). Stepped spray nozzles in the 21st century are simply another tuning option available to AMAL carby users.
"Dell Ortos on my Commando" may be the original thread concept I encourage you to initiate. Perhaps have a go at throttle pumped AMALs as an original thought - oh no, too late, I just thought that thought!
When you say "...We..." in your posts, perhaps you could disclose just how many voices do actually muttter away in there.

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Pumper amals have been done already ?
Some folks here still don't seem to appreciate the finer points of cut spray tubes, so the subject isn't done yet.
Even if all the informed discussion of them is 40+ years ago, which we are only now distantly recalling.

Why are we reinventing the amal wheel here, again, anyway ??

Rohan said:

"Dell Ortos on my Commando" may be the original thread concept I encourage you to initiate.

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They won't fit - not easily anyway. Looked at that already.
They are taller and wider than Amals, and the throttle action is up near the top.
Clashes with the tank.

Besides, as I mentioned, they are probably the only carb more finicky than an Amal.
The idle and synch always seemed to be out or need fiddling.
And they piddle fuel at the slightest opportunity. !

They are also 36 mm, which conventional wisdom has as being too big for a Commando.
Although maybe the accelerator pumps will handle that ?
Guzzi will handle 40mm, so maybe the cam (and 8000 rpms) is the answer to that enigma....

2 strokes develop less pressure differences between ambient and chamber on intake stroke than 4 strokes and some 4 strokes do not develop as much intake pressure flow differences as others so back to trial and error with what ever comprehension you can apply or just accidental experiments like BSA & me tripping over mis matched intake. Trouble is what might actually be a very good fueler improvement may not show up if exhaust not adapted to. Streamlining, ventri pinches and back wash turbulance and intake bounce out the throat confuse me no end. I know when ya get a do 750 stocker optimalized rear tire control and spares becomes next trial error experimenting.

Re: Needing Air to pick up fuel as it passes

An optimised pilot circuit first transitions at a minute slide opening where both pin holes are subject to Bernoulli effect. The next transition creates a lean condition until air speed and volume can draw enough fuel through the needle jet via the spray nozzle. This design resolves this condition by increasing the low pressure state at the spray nozzle earlier by restricting the air space beneath the throttle slide. The low pressure state increases air speed around/over the spray nozzle and therefore through the air compensation hole around the needle jet. The result is that fuel is available earlier for improved AFR and better atomised with increased air speed. Objectively: the proof of the tuning is on the dyno. Subjectively: the flat spot is noticeable by it's absence.
Ta.
Dear Rohan (and/or "We") Please provided all the original documented evidence of throttle pump enhanced AMAL Concentric Mark 1 carburettors that you claim exists. I'd just hate to re-invent that 'wheel' Ta.

Re: Needing Air to pick up fuel as it passes

needing said:

Dear Rohan (and/or "We") Please provided all the original documented evidence of throttle pump enhanced AMAL Concentric Mark 1 carburettors that you claim exists. I'd just hate to re-invent that 'wheel' Ta.

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Ta, do ya own searching, ya lazy git.
I don't claim to have invented it, just seen it in passing.

It was more complicated than I remembered...



Simpler way to instantly fix ailing amals.
Cut spray tubes included.

Rohan said:

Ludwig, my 850s have all had stepped spray tubes, no flat spot off idle.
Problem solved ! ..

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That may well be , but it does not explain what the stepped spray tube does , its relation to the 4 ringed needle ,
or why you had a flat spot in the first place .
(You did have a flat spot with straight cut tubes , right ? )

At the risk of oversimplifying things :
Larger main jet = richer .
Lowering needle = leaner .
higher float level = richer
More slide cut off = leaner .
Stepped spray tube = ?? .. start speculating .

Quoting someone who quotes from a book , in which the autor quotes someone who heared from an ex factory worker 40 years ago ...
Is not a satisfactory answer for me .
( or for Thomas ..)

NO, I DID NOT HAVE A FLAT SPOT.
You appear to have a mindset that is veering off into hobot land ?

As far as I know, all 850s came with the cutaway spray tube.
All the Amals for 850s I have seen have them.
Problem solved, before I'd even heard of it.

The Amal 2 stroke carbs have a different spray tube arrangement.
They were widely discussed back then though, if you hunt around.
http://velobanjogent.blogspot.com.au/20 ... paper.html

"Two alternative systems were developed, one for four stroke engines and one for two stroke engines, (inset), to give appropriate throttle range and compensation characteristics. These resulted in the need for alternative spray tube, needle and needle jet components."

"One system is virtually the monobloc principle, retained for four stroke engines but dimensionally more compact and maintaining approximately the same standard of performance, that is the compensation curve inclined towards richness at low speed wide open throttle."

"The second arrangement, developed specifically for two stroke engines, maintains tighter control over the fuel metering. A spray tube cutaway chamfered to the rear raises the effective depression across the jet, enabling smaller jets to be used for an equivalent fuel flow. "

This really is ancient history.....