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Anonymous
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Dear rohan.
You self proclaim to be the "proof reader" of this forum yet the 1978 scientific paper you quote to support your polemic is as incorrect as is much of the other AMAL liturature.
You will observe that their drawing "Fig 4 'Concentric' carburetter" does not even have a throttle slide cutaway - how can the rest of the paper be taken seriously now, in this, the 21st century. Please choose your historic (perhaps ancient, certainly redundant) documentation with greater care. I had hoped that you would contribute in a positively meaningful way but, Oh no: back under the bridge for you
.
Ta.
Reference: http://velobanjogent.blogspot.com.au/20 ... r.html?m=1
You self proclaim to be the "proof reader" of this forum yet the 1978 scientific paper you quote to support your polemic is as incorrect as is much of the other AMAL liturature.
You will observe that their drawing "Fig 4 'Concentric' carburetter" does not even have a throttle slide cutaway - how can the rest of the paper be taken seriously now, in this, the 21st century. Please choose your historic (perhaps ancient, certainly redundant) documentation with greater care. I had hoped that you would contribute in a positively meaningful way but, Oh no: back under the bridge for you
.Ta.
Reference: http://velobanjogent.blogspot.com.au/20 ... r.html?m=1
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Spray tubes work like a chimney faster draw out the longer it is but will leak smoke out easier if shorter and low pressure turbulance tumble is created if back edge is lower than leading edge. Could try to drill a small hole near its base to see if can get both earlier fuel spill out at low rpm throttle ups yet more fuel pull at hi flow rates.
At the mini Woodstocks out here they have bonfires hollow logs craved as TIKI gods stood up to catch fire out all openings so I have experimented with my hand and wood slabs on leading edge to mimic notched spray tubes for insights on how to profile chimney for better flow out. Also to reduce flow turbulence interfering with chimney draw out they can have spiral vanes added and sides made flater too.
At the mini Woodstocks out here they have bonfires hollow logs craved as TIKI gods stood up to catch fire out all openings so I have experimented with my hand and wood slabs on leading edge to mimic notched spray tubes for insights on how to profile chimney for better flow out. Also to reduce flow turbulence interfering with chimney draw out they can have spiral vanes added and sides made flater too.
ludwig said:
Did you READ that article ?
"rich" at "wide open throttle" are the operative words in any discussion of the stepped spray tubes. !!!!!!
This has been widely known for 40+ years.
That was someone from AMAL presented in that article.
I never had a flat spot problem, in any 850 - they ALL came with the stepped spray tubes.
Amal had solved that problem before I'd even heard of it...
Maybe I need to explain in 2 syllable words.
I bought those 2 new GENIUNE 850 amals back when I was rebuilding a crashed commando, that had sat in the open for several years.
The carbs were somewhat crusty, and new ones were either $40 the pair or maybe $40 each, not quite sure now.
I still have them, they are great for trouble shooting carbies.
Can chack that any rebuilt carbs function identically.
Just swap em over, and instant compare....
Capiche ?
needing said:Dear rohan.
You self proclaim to be the "proof reader" of this forum yet the 1978 scientific paper you quote to support your polemic is as incorrect as is much of the other AMAL liturature.
You will observe that their drawing "Fig 4 'Concentric' carburetter" does not even have a throttle slide cutaway - how can the rest of the paper be taken seriously now, in this, the 21st century. Please choose your historic (perhaps ancient, certainly redundant) documentation with greater care. I had hoped that you would contribute in a positively meaningful way but, Oh no: back into the box for you
You are getting deperate. AND somewhat condescending in your ignorance.
Is that the best nitpicking you can do....
That guy was from AMAL, and if one of the diagrams wasn't quite up to snuff, so be it.
He probably grabbed a draft copy of a prototype and didn't notice, who knows...
Stepped spray tubes in 850 AMAL carbs have been widely known for 40+ years now.
About time folks here caught up some, it would seem.
Actually Steve, the article mentions that the cutaway spray tube has the fuel level closer to the air flow,
so it draws out more fuel with wide open throttle.
So railway loco chimney example doesn't fit here.
Complicated stuff this aero magic.
These stepped spray tubes have been around half a lifetime already, seems some are still learning here...
Nice diagram, not sure what it shows.
Pretty though...
so it draws out more fuel with wide open throttle.
So railway loco chimney example doesn't fit here.
Complicated stuff this aero magic.
These stepped spray tubes have been around half a lifetime already, seems some are still learning here...
Nice diagram, not sure what it shows.
Pretty though...
hobot said:Spray tubes work like a chimney faster draw out the longer it is
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ugh, the word -read- origin means to quess. Two of one thing or a pair of em or a couple, as less distance for fuel to rise to spill out same as path of fuel closer to air flow. This better mean same thing to everyone here or just baiting w/o merit. Spray tubes are same thing a fireplace chimney (w/o the heat) which is also called -Stack Effect-. Spray height varies a bit and Amal said could vary over 10% difference w/o affecting the mixture which implies rear profile matters more that the front same as land speeders.
If someone that does not know of of this already, caring to experiment with spray tubes - I suggest instead of step/notch that just a couple of hack saw blade slices about 3/16 deep be tried and bevel the ID of leading rim of tube and file sides flat as ya dare. Then diddle float so pilot screw likes/invites less than one air diluting turn out.
Air cooled engines pressed into hi heat of WOT down low fuel burns and red lining tend to survive better with richness surppressing detonation because they do not have enough octane for full ign pressure advance quick nor water or methanol sprayer.
Needing there is a down dirty way to give Amals an accelerator pressure pump but for life of me can not understand why as none of ya ever seem willing to discuss to thrilling dangers of digital level traction response or immaturely using full power at every opportunity... Get enough low down into mid range response and better have water skiing reflexes down to the bone memory or just not taking advantage of your improvement. Surprise wheelies a risk so do not attempt at home. Less than this factory spec works fine.
If someone that does not know of of this already, caring to experiment with spray tubes - I suggest instead of step/notch that just a couple of hack saw blade slices about 3/16 deep be tried and bevel the ID of leading rim of tube and file sides flat as ya dare. Then diddle float so pilot screw likes/invites less than one air diluting turn out.
Air cooled engines pressed into hi heat of WOT down low fuel burns and red lining tend to survive better with richness surppressing detonation because they do not have enough octane for full ign pressure advance quick nor water or methanol sprayer.
Needing there is a down dirty way to give Amals an accelerator pressure pump but for life of me can not understand why as none of ya ever seem willing to discuss to thrilling dangers of digital level traction response or immaturely using full power at every opportunity... Get enough low down into mid range response and better have water skiing reflexes down to the bone memory or just not taking advantage of your improvement. Surprise wheelies a risk so do not attempt at home. Less than this factory spec works fine.
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Hi hobot.
Thanks for the colour picture of the needle. As you know, fuel struggles to 'climb' the walls of the needle jet itself and then break free at the lip due to surface tension. However, it 'climbs' the needle much more readily and is then whisked free by the jetstream of air that creates the Bernoulli effect that lifts it. I had not yet thought of spiral grooving (perhaps rifling type grooves) to the needle to enhance atomisation per your picture: thanks. A potential downside could be faster wear of the needle jet orifice by the groove edges if raised. My earlier experiment of drilling the needle jet was intended to improve capillary flow up the needle: I may yet revisit that one in light of viewing your picture.
This musing forms part of the phase 2 mods: the transition from slide/air channel to fully exposed spray nozzle and needle.
Ta.
PS: I can envisage a Mark 1 incorporated throttle pump but will call that one Phase 3 for the time being.
Thanks for the colour picture of the needle. As you know, fuel struggles to 'climb' the walls of the needle jet itself and then break free at the lip due to surface tension. However, it 'climbs' the needle much more readily and is then whisked free by the jetstream of air that creates the Bernoulli effect that lifts it. I had not yet thought of spiral grooving (perhaps rifling type grooves) to the needle to enhance atomisation per your picture: thanks. A potential downside could be faster wear of the needle jet orifice by the groove edges if raised. My earlier experiment of drilling the needle jet was intended to improve capillary flow up the needle: I may yet revisit that one in light of viewing your picture.
This musing forms part of the phase 2 mods: the transition from slide/air channel to fully exposed spray nozzle and needle.
Ta.
PS: I can envisage a Mark 1 incorporated throttle pump but will call that one Phase 3 for the time being.
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Ugh, look again and view image in correct prospective > its an Image of outside air flow on a fairly tal narrow chimney not as thin a profile as gasoline fuel needle - thought similar flows would be seen on needle IF the flow around the fuel needle was sideways to it - like it is for a spray tube, not rising up its flanks as needle in jet. Best I can get plain Amals to work by snap off 900 rpm idle is bit hesitation for a few rotations then takes off w/o stalling. Not my style expect is similar to lugging with cargo up grass steep must keep adding throttle to climb but not stall out nor spin out so exactly matches the official definition of Lugging, engine states where more throttle does not change engine speed but by golly is sure maintains torque or increasing it as grade steepens still as same sane speed for conditions and cargo. Un loaded and going below 30 its fun to snap Wot an instant for the rear kick out that stops almost as fast as let off.
The pressure gradients past spray tube will have some flow on floor rise up spray tube into lower pressure faster flow zone closer to center of throat, though may not be enough to matter at lowish rpms
The pressure gradients past spray tube will have some flow on floor rise up spray tube into lower pressure faster flow zone closer to center of throat, though may not be enough to matter at lowish rpms
hobot said:
No need to 'experiment' with spray tubes Steve.
This mod has been around for decades, I'm stunned that folks here don't know of it.
(let alone argue or deny that it works or how it works !!!, that is just hilarious).
Jim Mosher is the engine guru on other lists.
http://www.performanceindian.com/VinAmalMods.html
This mod has been around for yonks.
I have used 32mm 850 Amals on other things for decades, they are the best thing since sliced bread.
Just in case folks haven't looked into an Amal with the cutaway spray tube, this is a rough old view.
The brass bit down at the base of the needle is where all the action is, a half slice has been cut out of it - facing the inlet valve.
Apols for the poorish pic, had to do it flashless and out in the sun.
This is in an Amal 32mm from an 850, genuine factory fitted.
The brass bit down at the base of the needle is where all the action is, a half slice has been cut out of it - facing the inlet valve.
Apols for the poorish pic, had to do it flashless and out in the sun.
This is in an Amal 32mm from an 850, genuine factory fitted.
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Rohan said:
Does that mean it doesn't temporarily enrich the mixture just off idle?
Dunno, I've never explored precisely how they work - they just work, very well.
I met this decades ago, might have forgotten the finer points of it all, until memory jogged here lately.
It was widely discussed and printed back then.
Amal did a good job of setting them up to run just tickety boo.
Maybe someone could report the exhaust gas analysis of a dyno run,
might shed light on matters...
I met this decades ago, might have forgotten the finer points of it all, until memory jogged here lately.
It was widely discussed and printed back then.
Amal did a good job of setting them up to run just tickety boo.
Maybe someone could report the exhaust gas analysis of a dyno run,
might shed light on matters...
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Anonymous
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Hi hobot.
You see the chimney, I see the throttle needle, and I imagine improved airflow providing the motive force to draw fuel up spiral grooves cut into the parallel section to better achieve and maintain the fuel column.
From thread page 14 drawings and explanation, you can see that my design is optimised for the notched spray nozzle however the design can accommodate and improve flat top spray nozzles by increasing airspeed over them during transition from pilot circuit. The photos below show the difference between the underside of alloy slides compared to my revised design build into a polymer throttle slide prototype.
I am currently reviewing modern polymer characteristics to determine the best options for a consumable throttle slide that does not destroy the throttle body (as the current design and materials have done since inception). Although materials development has progressed exponentially since the late 1960's it is now obvious to me that some mindsets remain fixed in the 'Buy new stuff, even if new stuff is the same old stuff'.
Ideally, the throttle body should have lasted forever with only a relatively cheap throttle slide being replaced when worn beyond acceptable use limits.
Ta.
needing said:is now obvious to me that some mindsets remain fixed in the 'Buy new stuff, even if new stuff is the same old stuff'.
If thats the thinking though, why not just buy current new type bikes.
Perpetually reinventing the wheel is - just - reinventing the wheel ??
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Let us keep quoting :
In Duckworth's book , p 76 , Bob Rowley sais that the mythical flat spot appeared when doing roll on tests with an 850 for the American market .
" Nobody seemed to want to know about this " ( quote)
" I mentioned it in front of Dennis Poore , who thanked me ..." ( quote)
" By experimenting with different shapes and amounts of cutaway ...they arrived at a situation where the main jet size could be greatly reduced .
This had the effect of eliminating the flat spot ...etc .." ( quote )
So , what do we learn from this :
1. Bob (Wrecker) Rowley , one of the best test riders/developpers at the time , was the 1st to mention the problem .
2. It only showed up on 850's with muted peashooters . ( the black cap silencers came with the MK 1A )
3. Apparantly there was no problem with the 850's for the European market , who still had the straight cut tubes .
4 . He only talks about the cut off , not a word about the 4 ring needle , which is supposed to go with it .
5. Not a word about small throttle openings , where all the other tuning gurus are talking about .
More later ..
In Duckworth's book , p 76 , Bob Rowley sais that the mythical flat spot appeared when doing roll on tests with an 850 for the American market .
" Nobody seemed to want to know about this " ( quote)
" I mentioned it in front of Dennis Poore , who thanked me ..." ( quote)
" By experimenting with different shapes and amounts of cutaway ...they arrived at a situation where the main jet size could be greatly reduced .
This had the effect of eliminating the flat spot ...etc .." ( quote )
So , what do we learn from this :
1. Bob (Wrecker) Rowley , one of the best test riders/developpers at the time , was the 1st to mention the problem .
2. It only showed up on 850's with muted peashooters . ( the black cap silencers came with the MK 1A )
3. Apparantly there was no problem with the 850's for the European market , who still had the straight cut tubes .
4 . He only talks about the cut off , not a word about the 4 ring needle , which is supposed to go with it .
5. Not a word about small throttle openings , where all the other tuning gurus are talking about .
More later ..
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