Needing Air

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Your source for these ?

Amal shows 4 stages in their diagrams.
Waddya know, the pinhole does the IDLE fuel.
And phases into the needjet stage as soon as the slide lifts any, the slide cutaway still limiting the air (or it would be too weak).
The amount of cutaway being adjustable (with a file !) to get the mixture burnable.

For decades and decades and decades, carbs had no idle jets at all, we all should be aware.
It was ALL done off the needlejet.
Talk of idle rpms airflow being too weak to pull fuel up out of the well is nonsense, my old Triumph beltdrive banger will fire down to ~200 rpms,
and it ONLY has the needlejet arrangement. Actually my old sidebanger isn't remotely running yet, but other old Trumpys are...

A Mr Binks patented a 2 jet carb, to give an idle function, quite some years after the 1st motorcycles.
Took quite a while for this concept to be widely adopted too. Mid 1920s ?
Not sure if he was the 1st, and other carb makers had different solutions (to get around the patents mostly ?)
Hopethisillucidates.
 
A documentation update to better represent how my carbys are currently tuned.
This is still a work-in-progress. See page 6 for 40+ year old documentation.
Ta.
 
As I mostly commented on the spray tube thread.

----

Still a little flawed ?

Firstly, if the pilot jet is a 25 and the main jet is say a 250,
then the main jets 'efficiency' or 'effectiveness' or call it what you will,
is that the main jet is 10 TIMES BIGGER EFFECT than the pilot jets effect.
So why isn't it drawn like that - ITS NOT TO SCALE.
Maybe minor, but for something like this it wouldn't have been difficult to do correctly to begin with.

Nextly, in real life, all of those effects are stacked on top of each other.
For clarity, they have been spread out to show each one individually.
But, why aren't they spread out in any order, seems quite random.
If the pilot jet is shown on the bottom, then the main jet should have been up top.
And the effects of each component contributing towards full throttle effects shown in turn up from the pilot jet.
Cutaway, then etc etc etc.
Again only minor, but still a flaw.
 
Jobs to do:
1. Polish prototype slides
2. Test prototype slides
3. Dyno runs
4. Field trial 1000km
Ta.
PS: the Mk 1 4-stroke pilot bushing flows 20 ml/min. The screw-in 2-stroke pilot jet flows 25ml/min.
 
needing said:
PS: the Mk 1 4-stroke pilot bushing flows 20 ml/min. The screw-in 2-stroke pilot jet flows 25ml/min.
Click to expand...
At what head pressure?
 
I am fascinated by flowing and spinning things, especially the streamlined art deco shapes so delicious to see your neat slide bottom. With enough low down improvement it makes short shifting around a city or onto a hwy a delight too. I should send ya one of my simple slip in mods to try a run with too.
 
WZ507 said:
needing said:
PS: the Mk 1 4-stroke pilot bushing flows 20 ml/min. The screw-in 2-stroke pilot jet flows 25ml/min.
Click to expand...
At what head pressure?
Click to expand...
Oh, the usual, as found on any Norton Commando motorcycle fitted with AMAL Concentric Mark 1 carburettors.
Seriously, there is no hydraulic head for the pilot jets as the fuel level in the float bowls is below either of them.
Ta.
 
hobot said:
I am fascinated by flowing and spinning things, especially the streamlined art deco shapes so delicious to see your neat slide bottom. With enough low down improvement it makes short shifting around a city or onto a hwy a delight too. I should send ya one of my simple slip in mods to try a run with too.
Click to expand...
...and so you should, and send money too, lots of money to pay for an ever expanding test programme! :D
Once I have established a new benchmark for my bike then I can look at testing other's designs/theories for comparison to that baseline.
Ta.
 
Didn't Amal cease calibrating jet sizes in cc's per min, quite some decades back now ?

I came across this a good while back - one series of carbs, don't quite recall which (early monobloc ?), has 2 different versions of jets.
And depending where the inscribed line is on the jet signifies if its old series or new series of jets.
And, of course, the sizes don't correspond between the different types....
 
Needle jets are sized in inches. I think pilot and cold start jets are too.

Main jet numbers are related to flow, but I don't know exactly how, except bigger ones are bigger!
 
Triton Thrasher said:
Main jet numbers are related to flow, but I don't know exactly how, except bigger ones are bigger!
Click to expand...

Easy enough to figure out at what pressure. Set up a simple test; take a jet and keep on adding steady fuel pressure until you measure the flow rate corresponding to that jet.
 
Rohan said:
Didn't Amal cease calibrating jet sizes in cc's per min, quite some decades back now ?

I came across this a good while back - one series of carbs, don't quite recall which (early monobloc ?), has 2 different versions of jets.
And depending where the inscribed line is on the jet signifies if its old series or new series of jets.
And, of course, the sizes don't correspond between the different types....
Click to expand...

I cannot address any changes that may or may not have occurred with regards to what units AMAL calibrates jets. The following link discusses what they are apparently using for units. It also shows examples of the different cut spray tubes as well as describes the "old" versus "new" main jets.

http://amalcarb.co.uk/rebuilding-mark-1-concentric-carburetter
 
Hi Dances with Shrapnel.
Within the AMAL link you provided above, there are a number of other clarifications e.g.
1. "...Some later 850cc Norton Commandos use a spray tube with a square cutaway step..." - the "...some later 850cc..." implies that not all 850's had the stepped tube,
2. Regarding the pilot bush, AMAL mentions cleaning "...using a No 78 or 0.016"drill..." as well as "...The bush has a flow rate of equivalent to 20cc/min...",
3. "...needle jets are stamped to show their sizes in inches from 0.105 to 0.125...".
Ta.
Hi Triton Thrasher.
Which one is the 'cold start jet'?
Ta.
 
needing said:
Hi johnm.
Thanks for the interest.
As you know, each run costs $ so I have focussed on my own test program for my mods.
On page 10, there is a video of the last run in that series and as you can hear (more than see) Tony rolls the throttle on quite smoothly.
I did have the ignition timing set at 30°BTDC but found on the dyno that 32° gave an extra 2 horsepower. Even cold, it still starts fine with my phase 1 mods so I go with that for the time being.
As of today, the main jets are now 260s (were 220) as I only have 200, 220 or 260 in the cupboard. My theory is at 7K+ rpm I would probably want the mix to be richer than leaner. The next series of runs will define the mid flow for that jet. I don't go there much out on the real road so it is really academic. I have a long haul (1000km) ride planned for next week to trial the full suite of phase 1 mods.
I have also changed the spray nozzles for the flat tops and expect the transition from the pin holes to then be leaner because the nozzle lip is now higher a la hobot's assertion and my bench trials with the vacuum cleaner. Personally, I see the variety of spray nozzles available as modern day tuning options. The historic evolution is interesting but moot. If rohan was to specify a test program I would be more than happy to quote (here, we call that putting your money where your mouth is). :D
Ta.
PS: I perceive the 3 phases will provide smooth idle to WOT through all transitions with a rolling throttle. A snap-open throttle on a carby bike can only work if there is a throttle pump. Constant flow at each opening is easy, it is the changes to air speed with opening transitions that make it tricky.
Click to expand...

Hi Thanks for the answer. Im a bit late getting back because there is only one computer in Romania that can see this site :)

The mixture curve you are getting is much much better than any I have seen when dynoing my 500. But it has megaphones which are harder to tune in. I have had advice in the past from John Healy on the Britbike forum on how to improve this (very small changes in the needle jet hole) and now your experiments will give me further things to investigate when I finally return home.

Oh yes and the hp increase with more advance surprises me too. I have gone the other way and it seemed to work. 28 deg advance on my Dommie at 10.25 CR and 98 octane fuel. However I read once about a series of experiments with race engines and around 1 in 10 would run best with considerably different timing than the others. No explanation was given but one might suspect squish or small changes in chamber shape ?

Regards

John
 
needing said:
1. "...Some later 850cc Norton Commandos use a spray tube with a square cutaway step..." - the "...some later 850cc..." implies that not all 850's had the stepped tube,
Click to expand...

LAB posted somewhere here recently that the parts lists show the same stepped spray tube listed for ALL 850 Commandos.
There is no other number listed for the spray tube for the 850 models, so in Norton-land thats pretty conclusive.

Burlen is a recent comer to the scene, so they likely don't have full chapter and verse history of what went before....
 
needing said:
1. "...Some later 850cc Norton Commandos use a spray tube with a square cutaway step..." - the "...some later 850cc..." implies that not all 850's had the stepped tube,
Click to expand...

I think the person who wrote that seems to have either got it wrong (didn't check their own records?) or worded it badly? :roll:

I suppose it's not impossible that "some" 850s left the factory with flat-topped spray tubes, however, if so, then probably only a few early ones that were not destined for the US West Coast.
The stepped spray tubes are specifically mentioned in the introduction to "The New 850 Norton" issued to the press by the factory in early 1973, quote: "Cutaway spray tubes are fitted" so the stepped spray tubes must have been introduced either at, or at least very close to, the beginning of 850 production.
 
Hi L.A.B.
Re: your AMAL comment: "...I think the person who wrote that seems to have either got it wrong (didn't check their own records?) or worded it badly?...".
This may often be the case and epitomises much of their documentation that I reviewed to the point where I now ignore more than rely on it. I am intrigued that so many accept it unquestioningly.
Ta.
 
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