Carb spray tube - cut away = stepped

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Staytite

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Hi All,
I have just bought a pair of Amals jetted as per an 850 Mk1
(260 & 3 1/2 & 107 ....)
On inspection they have a cut away (stepped) spray tube sticking up into the air flow.

I thought the cut away spray tube was introduced by Norton on the late 850s due to the use of the plastic
air box and the anular silencers.

I am informed that the stepped spray tube is correct for the earlier paper type air filter and the straight
throug peea shooter silencers.

Does anybody know which is correct for the paper / peashooter combination used on the early 850s?

Thanks
Staytite
 
It might be more important that you have the 4 ring needle to match. I am sure that you do and it will work just fine.
 
For some reason, maybe the lower compression 850 lack of mixture draw in off idle, they stepped the spray tube to draw fuel up easier is all, and a secret weapon for 750's to get acceleration pump like response down low is to notch/step their spray tubes also. Two strokes that don't don't draw in mixture down low as well as a 4 stroke also get notched/cut/stepped spray tubes. So the spray tube back side or how high it sticks up should not mess with the basic needle and jet combo's per standard engine needs. Amal reported they tested carbs with differing height of spray tubes to report it did not alter mixture to matter but I still try to even the spray tubes similar in each Amal. Spray tubes are barely held in place by a textured grip fit so its a wonder to me they stay put with engine vibe and heat.
 
hobot said:
Spray tubes are barely held in place by a textured grip fit so its a wonder to me they stay put with engine vibe and heat.
Click to expand...
This is somewhat true but is fitted from the bottom and held in position by the jet holder. The serration on the spray tube lines it up, kinda like a key way, to face the proper direction. No worries! It is going no where.

Just to be clear, the 4 rings on the needle are for its ID and not the rings for the circlip as with a 2 ring needle for non cut a way spray tubes.
 
Staytite said:
I thought the cut away spray tube was introduced by Norton on the late 850s due to the use of the plastic
air box and the anular silencers.
Click to expand...

I think perhaps many would agree, however, all three parts lists for '73 850, 850 Mk1A and '74 850 Mk2 & 2A only mentions the "928/104" (4 ID ring) needle ("Use with Spray Tube 928/107") and "928/107 Spray Tube".

The only apparent difference is that the Mk1A parts supplement refers to the 1A carbs having 230 main jets and .106 needle jets.
 
Hi All,

Thanks for the replies.

It seems strange to me that the Mk 1 suplement gives the 220 main jets as I would have thought with
the paper air box and peashooters on the Mk 1 the bigger 260 jet would be fitted.

I need to check the ID of the needle fitted to my new carbs to see if it is correct for the cut-away
spray tube.

Are we sure the parts books reflected what was actually fitted in the early 1970s?
I still think I remember the full spray tubes (and associated needle) on the paper/peashooter 850s
and the cut-away spray tube for the plastic airbox/ anular. And when changing to the paper/peashooter
I also changed to the full spray tube (and associated needle) and with 260 main jets.

Does anybody else have the same recolections?

Thanks
Staytite
 
the cut-away spraytubbes were indeed used on mk3 (electic start and bean-cans)
normally these cut -aways are for 2stroke appication only but for some reason they seemed to work fine on the later commandos
for earlier commandos (pre bean cans)one should use full spray tubes

(source ; mr B Johnston AMAL 1992)

when using cutaways on the kneeler we could not get the carburation spot on , and all kind of 'advice 'was given ,in the best intentions, but only after we knocked the half ones out and put complete ones in , did we get what we wanted
This was after i contacted AMAL to get the answer from the horses mouth

needles etc should bet set according to what you use as engine/exhoust etc , as on the outfit we ran a 2 into 1 big bore ,and long bellmouths so nothing standard
 
Staytite said:
It seems strange to me that the Mk 1 suplement gives the 220 main jets as I would have thought with
the paper air box and peashooters on the Mk 1 the bigger 260 jet would be fitted.
Click to expand...


I think you may have misunderstood.

I said:
L.A.B. said:
The only apparent difference is that the Mk1A parts supplement refers to the 1A carbs having 230 main jets and .106 needle jets.
Click to expand...

The supplement is for the 850 Mk1A model that had the black airbox and A/D silencers, not the 850 Mk1 which is covered by the 1973 750-850 part list.

(also 230 not 220).
 
you can got to the Amal sight and check settings and components of the carb for your Norton model. Pretty sure cut away spray tubes with the 4 ring ID needles were found best for 850's. I read somewhere back in the day the 850 gave the factory trouble in the clean carburettion and Amal and factory reps got together and after much experimentation came up with the two stroke style spray tube, all the tubes are there to pool fuel around the base, together with providing a certain spay pattern. Straight cut a pretty common, Tridents need a angled pattern to run well.

Cheers Richard
 
Hi Richard et al

Thanks for the reply. However I think your referance to problems fueling of 850s being a problem
was due to the plastic air box and "bean-can" anular silencers being forced upon the 850 Commando
to meet the new emmision/noise regulations of about 1973/4 (UK or USA or both?).

I still think there is a big difference required for the carbs of the 850+plastic+anular compared to
the 850+paper+peashooter. One being the cut away for the spray tube of the former and the full tube f
or the later such that both rum cleanly.

Thanks to all

Regards
Staytite
 
Staytite said:
I still think there is a big difference required for the carbs of the 850+plastic+anular compared to
the 850+paper+peashooter. One being the cut away for the spray tube of the former and the full tube f
or the later such that both rum cleanly.
Click to expand...


My copy of the book "Norton Commando Gold Portfolio" contains an article published in the April 1973 issue of Motorcycle Sport which is entitled: "The New Big Norton" and it outlines the various detail improvements of the new Commando 850.

Listed as item 19
19.
Carburettor ticklers are now of "waterproof" Spanish type.
The float bowls are fitted with drain plugs.
Cutaway spray tubes are fitted.
Click to expand...

As this feature was published some months prior to the introduction of the Mk 1A model it does seem to suggest that cutaway spray tubes were fitted from around the beginning of 850 production.
The 1973 750-850 parts book also lists only the 928/107 stepped spray tube and 928/104 (4 ring) needle and the factory manual gives the same information also listing the needle jet as: .106, so according to the manuals and parts books at least, the difference between non-A and A models appears to have been basically down to main jet size. Why the Mk 1A supplement specifically refers to a: ".106 needle jet" remains a mystery if all 850's supposedly had them?
 
I've been happily running non-cutaway spray tubes in an 850 for years. Seat of the pants told me that it felt better that way, although the difference was small.

I use a 750 air box with flat front plate 060902. However, the late 750 / 850 parts book includes a drawing of a front plate with a deep 'mouth' into the filter area with a half-round inlet tube below. Could the cutaway tube be related to this interim perhaps more restrictive and quieter induction system which still used the paper filter, and then continued with the black plastic system ?

I have to say that they appear to have mixed up the item numbers in the drawing as the part previously labelled as 060902 Front Plate 750 Air Cleaner is now shown as 063813 Front Plate 850 Air Cleaner and the new-fangled part is marked for the 750 and shown as 060902. :?
 
L.A.B. said:
Staytite said:
I still think there is a big difference required for the carbs of the 850+plastic+anular compared to
the 850+paper+peashooter. One being the cut away for the spray tube of the former and the full tube f
or the later such that both rum cleanly.
Click to expand...


My copy of the book "Norton Commando Gold Portfolio" contains an article published in the April 1973 issue of Motorcycle Sport which is entitled: "The New Big Norton" and it outlines the various detail improvements of the new Commando 850.
Click to expand...

I would never take a magazine article as gospel. Nor a factory press release. They are usually based on pre-production information and can easily be changed later.
 
swooshdave said:
L.A.B. said:
Staytite said:
I still think there is a big difference required for the carbs of the 850+plastic+anular compared to
the 850+paper+peashooter. One being the cut away for the spray tube of the former and the full tube f
or the later such that both rum cleanly.
Click to expand...


My copy of the book "Norton Commando Gold Portfolio" contains an article published in the April 1973 issue of Motorcycle Sport which is entitled: "The New Big Norton" and it outlines the various detail improvements of the new Commando 850.
Click to expand...

I would never take a magazine article as gospel. Nor a factory press release. They are usually based on pre-production information and can easily be changed later.
Click to expand...

I would be inclined to agree-if the factory parts book for '73 did not also contain the same information. That parts book does not cover the 1A model.
The '74 Mk 2 & Mk 2A parts supplement also does not list any alternative spray tube and needle for the Mk 2 model.
 
Re: Carb spray tube - full tube or cut away or chamfered

Hi All,

I have found a bit more time to investigate....I was in a quarry previously (supposedly working).

I have found much theory and information on the Norton Owners Club web site.

Go to NOC web site ....Technical....Commando...Carburettor

It would seem the same discussion I started this week on sprat tubes also took place in 1998!

For those who have time to read it is interesting stuff. I am leaning towards fitting my new Amals with the cut aways
rather than full tube type.....or where can I get some chamfered ones?.....decisions....decisions....there were only two
choices now there are three!

Thanks for any thoughts on the 1998 data on the NOC web site

Cheers
Staytite
 
Hehe, I cut my Cdo teeth on NOC from the UK so suggest you don't buy new spray tubes, until you've pushed out your current flat tops and trimmed them a bit by a notch or slot or step, to see if you can handle the accelerator pump effect. DIY allows ya to creep up on the effect. Basically two things happening, one less height for air flow to over come fuel gravity and two some extra back side suction to pull fuel out a bit more sooner. I'd also file the sides of the spray tubes a bit to streamline them a tad.
 
Spray tubes are available at the Amal site. I have, and you can, cut your own to what every notch or angle you wish. Be sure to have both types of needles on hand and be prepared to do some tuning. I have gone through the gamut of 2 ring, 4 ring, notch, no notch and all combinations there of.

No 2 Nortons breathe exactly alike. Compression, bore size( 20 over, 40 over etc.) different exhaust and many more aspects all play a part in carb setup. Make your best guess to start with then start the analysis. Eyes, ears, smell and feel. There are generalities and you may hit a home run right of the bat, but if you are anything like me, you will go to extremes to validate. That's just my way of having fun.

Also, make sure your cam and ignition timing is right before delving into such practices. You could waste days with no good results if all ducks are not in line.
 
Hi All,

I was not intending to re-invent the wheel. Surely somebody knows whether the spray tube on an
850 with paper air box and peashooters was originally fitted with a cut away spray tube or not?

Regards
Staytite
 
Staytite said:
Hi All,

I was not intending to re-invent the wheel. Surely somebody knows whether the spray tube on an
850 with paper air box and peashooters was originally fitted with a cut away spray tube or not?

Regards
Staytite
Click to expand...
I gotta say and this thread sort of begs the question, are you more concerned with purity or functionality?

I am not saying it is so, but you are right in that range where it could have had either.
 
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