Needing Air

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Re: Needing Air to flow where you want it

How a sealed throttle slide/body junction and the initial few millimetres of throttle slide opening improves tuning control. Pictures may assist for those having difficultly conceptualising. I hope it helps.
Ta.
 
My pilot circuit does not pass enough air to run the engine with the throttle slide right down, no matter what I do with the mixture screw.

Why is yours different?
 
Triton Thrasher said:
My pilot circuit does not pass enough air to run the engine with the throttle slide right down, no matter what I do with the mixture screw.

Why is yours different?
Click to expand...

Neither would mine until I sealed the throttle slide skirt/body junction.
Do your slide skirts actually bottom out or do the cables hold them up just a little bit?
Ta.
 
needing said:
Do your slide skirts actually bottom out or do the cables hold them up just a little bit?
Click to expand...

You can set the throttle cables so the slides hit the bottom.

It should be the adjuster screws that holds them up enough to be able to idle.
In conjuction with the mixture screws...
 
Re: Needing Air and balancing fuel

Stage 2
Just drilled carby set 2 to balance the pilot fuel feed lines from the float bowls. The picture that is pasted-up originally showed drilled and tapped pilot jet access screws: this mod simply goes one step further to provide ready access for checking and cleaning of the pilot jet orifices (you can see through both carbies via the pilot circuits).
Photo and paste-up should clarify.
Ta.

Edit: other carby sets now drilled for balance tubes.
Pilot fuel flow and manifold pressures are now balancing each other.
Now for Stage 3.
 
needing said:
Triton Thrasher said:
My pilot circuit does not pass enough air to run the engine with the throttle slide right down, no matter what I do with the mixture screw.

Why is yours different?
Click to expand...

Neither would mine until I sealed the throttle slide skirt/body junction.
Do your slide skirts actually bottom out or do the cables hold them up just a little bit?
Ta.
Click to expand...

The cables are adjusted so both slides hit the bottom. Then they're lifted with the throttle stops, far enough for a reliable idle, with a bit of adjustment to the mixture screws.

TRhat's kind of what everyone does.
 
Triton Thrasher said:
needing said:
Triton Thrasher said:
My pilot circuit does not pass enough air to run the engine with the throttle slide right down, no matter what I do with the mixture screw.

Why is yours different?
Click to expand...

Neither would mine until I sealed the throttle slide skirt/body junction.
Do your slide skirts actually bottom out or do the cables hold them up just a little bit?
Ta.
Click to expand...

The cables are adjusted so both slides hit the bottom. Then they're lifted with the throttle stops, far enough for a reliable idle, with a bit of adjustment to the mixture screws.

TRhat's kind of what everyone does.
Click to expand...

Hi Triton Thrasher.
The initial reason for sealing the junction was when I discovered new alloy AMAL throttle slides are not flat across the base of the skirts (wiped one across a sheet of 1200grit paper backed by a sheet of glass to check). I flattened the skirt face but this still did not effectively control the all airflow hence the seal on the 'old' sets as well as brass slides then a 'newer' set of carby bodies. From the video you will notice I use an Air:Fuel Ratio and Exhaust Gas Temperature gauges to optimise tuning. If you are using trail and error tuning methods without incorporating a seal then I suspect you will struggle to achieve steady idle even with the slides bottomed out. I have seven stages of mods planned, two are completed as of today. Trials tomorrow.
It is my opinion that alloy slides 'hitting' the carby body is the primary cause of the skirts breaking off and being ingested by the engine (another reason for the seal/buffer).
Ta.
PS: I am not counting the grubscrew mod and tapering needle jet lips as tuning 'stages'. They just needed to be done to make the carbys robust i.e. less failure prone by design.
 
Re: Needing Air and fuel to flow one way only

Stage 3 machined.
Self priming, non-return valves fitted to the pilot fuel circuits. The cut seats have a 3/16" steel ball drift tapped to form an air tight oneway seal (tested with a piece of tube and lungs :D ). With the sealed throttle slide fully shut, I envisage the first cold kick will prime the pilot circuit and start the engine (without flooding/tickling is the goal). Chokes have been redundant on my bike since the 1980s.
Ta.
 
Re: Needing Air to reduce pilot circuit surge

This is the rationale for Stage 2 (linked pilot circuits) and Stage 3 (oneway pilot fuel flow).
Hopefully, this picture will save 982 words from consumption. :D
Ta.
 
Re: Needing Air effectively

Ever seen this diagram?
Needle taper activation can be shown more to the RH or LH depending on clip position (as can 'straight dia.' deactivation.
So, I ask, why is 'clip position' shown on this picture? It has no active role except to show when needle taper begins to take effect and straight dia. ceases. Aha, says I, if you were to read 'needle jet' in place of 'clip position' then tuning AMALs will become such a simple matter. :D
Does anyone know of a corrected diagram issued by AMAL over the decades?
Ta.
The 4-ring needles (928/104) arrived today. Same parallel diameter (2.5mm) as the 2-ring (622/124) but the taper/length differs. Stage 1 of Phase 2 now begins.
 
Checked the throttle slide to body clearance on old carby sets today. Set 2 are original fitment, Set 3 is the first replacement set and Set 1 (currently on the bike) are recent acquisitions. The thottle slides were all set for checking at a consistent opening using the stop screws to accept a 1.5mm drill bit.
All carby sets use the float bowls from Set 3 to ensure a consistent float height for tuning.
Ta.
 
You removed the chokes , but did you do anything to the underside of your slides ? .
Sealing the slides with a curved plate will give you better throttle respons .
something like this :
Needing Air
 
Thanks ludwig.
I spotted that one on an earlier post of yours and it is on the list for phase 2.
Any other tweaks I can trial while I'm looking at carbys?
Ta.
PS: how are the screws locked so they can't come out and be ingested?
 
Not sure if the slide in the pic is pot metal , or the new alloy slides .
In the old pot metal slides , there is room for a nut on the inside .
The new alloy slides have plenty of material to thread and loctite .
Even if more massive , they are also lighter then the old ones .
I would recommend to use the new ones .
Other tip : shorten the brass needle seat in the float bowl , or cut slots , so that the bowl fills quicker .
And remove that useless big O-ring that seals the flange against the manifolds . It only helps to distort the carb body ..
 
Re: Needing Air to flow smoothly under the throttle slide

ludwig said:
Not sure if the slide in the pic is pot metal , or the new alloy slides .
In the old pot metal slides , there is room for a nut on the inside .
The new alloy slides have plenty of material to thread and loctite .
Even if more massive , they are also lighter then the old ones .
I would recommend to use the new ones .
Other tip : shorten the brass needle seat in the float bowl , or cut slots , so that the bowl fills quicker .
And remove that useless big O-ring that seals the flange against the manifolds . It only helps to distort the carb body ..
Click to expand...

Thanks ludwig.
Page 2 of this thread shows the slots that I cut into the bowls for fuel flow.
I have the gaskets that came in a kit but I went with the o-rings. Gaskets make better sense and the o-rings seal the topcap joint well (with distortion spacers)
I have brass slides (much heavier re page 2) but I'll have a think on how to eliminate the screw risk.
Ta.
Ps: if throttle slide/body seals, joined pilot circuits and one-way pilot fuel flow can collectively overcome the worn body/slide clearances (shown above) to allow the stop screws to be eliminated then the slide cutouts could be modified to retain the choke covers, maybe. Hmmm.
 
Do peashooter mufflers have full length perforated pipe that abutts the header exit, effectively defeating the measured header length concept? How are the internals of blackcap mufflers constructed? i.e. do they allow a finite header length as part of their design? Does anyone have a cutaway view (or sketch) of both types to share?
Ta.
 
Planning some 4000rpm noise reduction tests soon. Please post if there are results already out there.
Ta.
 
Re: Needing Air to draw fuel closer to jet orrifice

Stage 1 of Phase 2 complete.
Spray tube ID = 6.30mm
Needle jet tube OD = 5.08mm
Annulus area plus two needle jets through-hole total area = 6 larger needle jets through-hole total area.
Result = air draws fuel near jet orifice if annulus is sealed. Stepped spray tube provides better atomised air:fuel charge to improve transition from idle during cutaway phase.
Ta.
 
I've seen advice that enlarging the two bleed holes in the needle jet by more than 10 thou stops fuel being drawn up to the venturi.

Be careful of what you've done to the air compensation by sealing the outside of the needle jet to the spray tube. You may find mixture varying with rpm.
 
Triton Thrasher said:
I've seen advice that enlarging the two bleed holes in the needle jet by more than 10 thou stops fuel being drawn up to the venturi.

Be careful of what you've done to the air compensation by sealing the outside of the needle jet to the spray tube. You may find mixture varying with rpm.
Click to expand...

Thanks Triton Thrasher.
My experimentation is based airflows for current AMAL air passages. If it doesn't pan out I just revert to standard, scrap a few jets, and rethink a bit harder. Do you know if the +0.010" was with the annulus sealed or open?
Did you get the idle speed sorted? I'm thinking that slides without stop cutouts will be stronger so hope that the sealed slide/body junction mod can be replicated. Are your bodies and slides very worn? perhaps the linked carbys and ball valve mod will overcome leaks around the slides.
Ta again.
PS: the float bowls are sealed so air compensation is provided by the ticklers. I haven't touched them yet but will keep them for that function and looks.
 
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