Rowley's 1/4 mile and the Magic Tube .

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Rohan said:
Triton Thrasher said:
"Straight diameter" is the metering by the parallel part of the needle in the needle jet.
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So why is 'clip position' at the top of the chart ??
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Aha!

I think I see now. You are reading the vertical axis as though it had zero at the bottom and ten at the top.

The vertical placing of the shaded blocks doesn't matter. It's the vertical depth from the bottom of a block to its top that indicates its influence on mixture at the throttle opening on the horizonal axis.
 
So can we move the main jet section to the top, and it makes no difference ?
So its saying there are 7 different zones of carby operation ?? (no surprises there, but we seem to be gaining them).

What would your definition of 'effectiveness' be then, if its not an axis on a graph ???
 
Rohan said:
So can we move the main jet section to the top, and it makes no difference ?
So its saying there are 7 different zones of carby operation ?? (no surprises there, but we seem to be gaining them).

What would your definition of 'effectiveness' be then, if its not an axis on a graph ???
Click to expand...

This chart appears on bushman's amal carb tuning notes, I thought these were very well known to those of us who have got their hands dirty with amals, whether by choice or necessity!
 
Rohan said:
So can we move the main jet section to the top, and it makes no difference ?
So its saying there are 7 different zones of carby operation ?? (no surprises there, but we seem to be gaining them).

What would your definition of 'effectiveness' be then, if its not an axis on a graph ???
Click to expand...

I didn't draw the graph.

I didn't understand it at first, either.
 
I reviewed and suggested the correction for that AMAL jetting chart on page 6 of 'Needing Air'. Keep up.
Ta.
 
needing said:
I reviewed and suggested the correction for that AMAL jetting chart on page 6 of 'Needing Air'. Keep up.
Ta.
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Have you corrected it yet?

If not, then what are we supposed to keep up with?
 
Triton Thrasher said:
needing said:
I reviewed and suggested the correction for that AMAL jetting chart on page 6 of 'Needing Air'. Keep up.
Ta.
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Have you corrected it yet?

If not, then what are we supposed to keep up with?
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Sure did. It is pinned up in my shed and the correction suggested on page 6 (Needing Air). Have you updated yours?
I no longer suggest corrections to AMAL/Burlens as they have yet not made changes to the other 40+ year old info they still have on their website.
Ta.
 
Rohan said:
What would your definition of 'effectiveness' be then, if its not an axis on a graph ???
Click to expand...

Rohan,

Try replacing the term "effectiveness" with "relative influence".

As stated earlier, there is no "absolute zero" on this graph's vertical axis as it is stacking various carb functions for relative comparison purposes.

I hope this helps to clarify.
 
I have answered this thread on page 4 but will state outright for clarity: In real world use, stepped spray nozzles on any Norton will create a rich mixture at low revs i.e. at 1.5 to 6.5 mm of throttle slide opening. That is why so many people complain of carbon fouled plugs.
Ta.
Edit: chart quick-fixed for others to use.
 
I've probably got a little confused, but the needle jet and spray tube are not the same they are different items. A two stroke spray tube is usually stepped be it Amal Bing or Mic'

I was taught it like the air correction jet influenced the depression in the primary mixing chamber and that is the reason two strokes generally have stepped or slanted spray tubes and smaller air correction jets was to drag out more fuel and oil.

I'm also pretty sure my Mk1 850 had four stroke spray tubes

Dave
 
Probably gonna go "DOH" after this question . In the chart, on the far left "I.M.S." is overlapped on "air screw slow jet". What does "I.M.S." represent?
 
Deets55 said:
best guess would be idle mixture screw?
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That's kind of what I thought so maybe this is a generic chart as any carb I've ever come across, that has a separate idle circuit, controls the mix with either an air screw, or a fuel screw, not both. The chart covers both... Pick your flavor.
 
Also, and apologies to those actually read both thread, I'd like to post here what I mistakenly posted on the hijacked one.

Sorry, but that one is just getting too bizarre what with upside down airplanes and all. Next they'll be discussing whether helicopters, bumble bees, and butterflies should be able to fly at all. :mrgreen:

This is an interesting topic as far as I'm concerned. Especially when we are still talking about Amal carbs and not so much airplane wings.
If a notched spray tube richens the mix at super low test drive-bys enough to prevent the Norton from totally bogging, which I believe is the case, then it stands to reason that same style spray tube would cause a too rich mix at higher revs as well. And so I believe the smaller 230's will under these conditions, deliver as much fuel as the previously fitted 260's because of the stronger vacuum signal at the float bowl keeping the mix correct. Would also explain to me why my own MK3, now fitted with straight through pea-shooters and a K&N filter does best with a jet increase to only 240. Previous to this thread I never gave this much thought, but now I think that being equipped with it's original notched tubed Amals, my Norton's engine would be getting too rich a mix with 260's regardless of muffler type, and is in fact getting the same (correct) amount of fuel throughout the range as a machine equipped with 260 main jets but with a straight cut spray tube.
Further, and forgive me if I'm wrong, but I believe there was questions about why 260's were OK for a while in the 850 with no apparent bog problem. Well it has been asked who in the world would actually routinely try to accelerate at WOT from such low revs? Nobody. So the 'problem' was only caused when the bikes had to pass such a ridicules sound test.
My final deduction: Engines equipped with Norton style notched spray tubes require smaller jets than identically set up engines with straight cut spray tubes regardless of intake or exhaust. (as long as intake and exhaust is also the same)
My last sentence may sound a bit snotty, as if I'm making believe I'm some sort of authority here. I don't mean it to, just using plane language that came into my plane head.

Biscuit Posts: 445Joined: Mon Sep 10, 2012 10:12 pmLocation: NH. USA
 
And this, a bit out of context but having to do with why smaller jets may work with a notched spray tube.....I'm thinking notched spray tubes in a 750's carburetor's would also necessitate smaller mains for the exact same reasons. As a matter of thought, Triumphs and BSAs would probably act the same way. That is; equipped with notched spray tube'd Amal carburetors, a given engine will need smaller main jets.

I really like brainstorming about carburation. I wish we were all out in my back yard playing music and drinking beer
 
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