Needing Air

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Rohan said:
An electrically operated switch at the end of twist grip travel to operate a solenoid give it a shot of fuel - and a little leccy fuel pump to supply the pressure.
Sort of a proto fuel injection nozzle, with no intelligence...

Of course, you could cut away the spray tube to do it the Amal way....
.
Click to expand...

So Rohan ,
you know for sure that the cut away enriches the mixture at low throttle openings , and that it prevents a flat spot when snapping open the throttle , right ? .
You have stated , or at least insinuated it countless times in this thread .
Can you please answer with a simple : " Yes " or " No " ? .

( what is it gonne be boy , YES , or NO ? ..)
 
Ludwig, the Amals haven't come into my office and signed a confession, so we cannot be ABSOLUTELY sure whats on their mind.
And I haven't interrogated them....


That Amal man, quoted back in that article back in 1978

"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."

I can recall similar stuff in magazine technical stuff back then, but I haven't thought any further on it for decades...

ESPECIALLY NOTE that phrase - "the compensation curve inclined towards richness at low speed wide open throttle."
That is pretty clear, is it not.
 
Rohan said:
The Amal blurb talks of a tube of fuel/froth available for enriching duties if the throttle is opened suddenly,
which is what triton is speaking of... (?).
Does the same job as an accelerator pump.
Click to expand...

Yes.

The section of the needle jet, above the bleed holes, is passing "emulsion" (froth) up to the venturi.

Apparently, when you grab a handful of throttle, to zoom past the car in front, some extra froth is briefly sucked up.

I'm not pontificating as a self-styled expert- I shortened the needle jet tops and obseved that it badly messed up the transition from "cruise" to "accelerate."

I was trying to improve the transition from "over-run," to "accelerate," but it didn't work.
 
And mine (Amals) work, quite well, and I haven't experienced a flat spot, so I haven't measured anything.
And as that little pic I showed show, they have the cutaway spray tubes.
Although my current 850 project is not quite there yet, been somewhat leisurely. (too many bikes ?).

I'd comment I also have a couple more of those carbs, for various projects,
including a pair for a Austin Healey Sprite.
Haven't tried them yet, though.

I'd further comment, again, that my 850 Lemans has pumper Dell Ortos,
and that shot-of-fuel out of the accelerator pumps ( and accompanying puffs of black smoke) give VERY strong acceleration.
As any carburetted airplane operator knows, max acceleration is FULL RICH for takeoff !

I have also mentioned here disconnecting the accelerator pump on my old V8 - and the acceleration was woeful, to put it mildly.
Dangerous even, although the fuel consumption halved !! (Country vs city miles though.)
Makeofthatwhatyouwill.
 
Rohan said:
An electrically operated switch at the end of twist grip travel to operate a solenoid give it a shot of fuel - and a little leccy fuel pump to supply the pressure.
Sort of a proto fuel injection nozzle, with no intelligence...

..
Click to expand...

The car (1960s Vauxhall) carburettors I had, with accelerator pumps, had mechanical means of only letting the pump work when you suddenly pressed the throttle.

Gentle pressing of the throttle didn't result in a spray of extra fuel.
 
Rohan said:
Dano said:
Good on you Ludwig love your work
Click to expand...

Even if he hasn't read that Amal mans spiel, or absorbed it. !
Needless either, it seems...
Click to expand...

Maybe I did ?

Ok Rohan , because I am such a nice guy , I will soften the question for you :

Do you BELIEVE that the cut spray tube enrichens the mixture at low throttle openings , and that it is a cure for flat spots ?

YES , or NO ?

( don't sleep on it . I've got to know right now ..)
 
needing said:
Rohan said:
The Amal blurb talks of a tube of fuel/froth available for enriching duties if the throttle is opened suddenly,
which is what triton is speaking of... (?).
Does the same job as an accelerator pump. [What a load of rubbish!]
Click to expand...

Real world Reality 1: Mk 1's do not have anything that resembles or functions as an accelerator pump
Click to expand...

I'd say it has a temporary enrichment function, for sudden acceleration.

Real world Reality 2: Fuel 'froth' collapses the moment the throttle slide is closed.
Click to expand...

Could be. But some fuel does still go via the needle jet while the throttle is closed, because it's not usually completely closed, but held slightly open by the throttle stop screw.

The difference I noticed with butchered needle jets was transition from (approx) 1/4 throttle to (approx) 2/3 throttle.
 
Ludwig, Thats what the Amal man said.
Who am I to deny what the man hisself said.

Accelerator pumps work BECAUSE they enrich the mixture.
Amal have found a similar effect, without actually needing a pump to do it ?
 
I offered that electrical triggering only as a simple way of adding an accelerator pump to a Commando.

My Lemon has fuel pumps on the pumper Dell Ortos, and they deliver a real stream of petrol.
HUGE puff of black smoke, and vast acceleration.
Some while back I (briefly) had a ride on a Guzzi with lightened flywheel - 2kg alloy one - and it would spin the back wheel on twisting the throttle hard.
Great fun in the dry, but I reckon it would be lethal in the wet.

Pumper Dell Ortos are big carbs, no chance of getting them in between the narrow frame tubes in a Commando.
Might get one only though, if it was mounted a little lower, with suitable manifold.
 
usually ??

Not sure I want to experience an unusual takeoff.....

But we diverge.
 
[quote="Triton Thrasher"
Gentle pressing of the throttle didn't result in a spray of extra fuel.[/quote]

Quite so.
Its only a brief spray too.

In US slang, accelerator pumps are also termed 'bore washers'.
The stream of fuel does have that effect, could imagine engine wear would be affected with a lot of it...
 
Rohan said:
Ludwig, Thats what the Amal man said.
Who am I to deny what the man hisself said.
Click to expand...


Rohan said:
ESPECIALLY NOTE that phrase - "the compensation curve inclined towards richness at low speed wide open throttle."
That is pretty clear, is it not.
Click to expand...

Ok Rohan , although you keep dodging the question , I will put you in the camp of the " enrichers " .

Now , what do you make of this :

John Heayley's explanation :
". I understood that by cutting the spray tube you disrupted the normal Bernulli/venturi effect of the spray tube at low throttle openings. That is, it would present a softer signal (difference between atmospheric and manifold vacuum) to the needle jet and air intake around the needle jet. But why do we need to soften the signal one the needle jet/air at low throttle openings?

The answer came from Kevin Cameron. Kevin is considered by some to be a world class 2 stroke tuner. He is a hero among many Canadian snowmobile tuners. He spent years, along with Kawasaki factory engineers devloping their TZ750D race bike.

He explained that a 2 stroke piston-port engine (not rotary port) has a short, but sharp drop in vacuum as the piston opens the intake port. The piston is going up, which creates a vacuum in the motor's crankcase. This vacuum builds until it is released, in what he calls a "pop," when the piston finally opens the intake port. This short, but intensive decrease in vacuum would draw too much fuel from the needle jet if the spray tube was not modified (made less effective). This effect one the spray tube is most apparent at low throttle openings.

Without the aid of on-board computers an engine tuner is stuck witht the fact that his selections must be a compromise. He is trying to get, what some tuners call "flat" carburation. That is the carb delivers the proper mixture from idle to full throttle. There is no radical variations, as presented to 2 stoke tuners with the "pop"

He must do thisto meet rider styles, atmospheric changes, enviromental rules, and any anticipated modifications to the bike. One such change is Norton's use of the stepped spray tube to lean the bike out at low throttle openings to meet EPA requirements. Other times, such as the sloped spray tubes in the T150, to effects on intake manifold pressure caused by exhaust systems." (quote )


Once again :

. One such change is Norton's use of the stepped spray tube to lean the bike out at low throttle openings to meet EPA requirements.

What do you think , Rohan ?

( take your time ..)
 
As I said, I just know they work, have never explored how or why.

Ludwig denies they work ?!
Needless either isn't sure, or can't put it into words... ??
 
Maybe we need to ask here which bikes got what carbs - and were there different versions of carbs, for different bikes.

I've never had anything to do with the Mk1A, Mk2A or Mk3 bikes.
But my 850s got the cutaway spray tube carbs.
Why would that be, if they didn't need to meet emissions standards ?
Or did all 850s get the same carbs ? (which I had understood, but not really explored).
 
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