6 part air adjuster kit to fit original Amal TT, RN and GP competition carburetters, containing the following parts: - Air cable adjuster and locknut - Air barrel top - Air valve and nipple holder for air valve - Air valve spring.  CNC manufactured (in stainless steel for top pieces, and brass for slide and barrel) to the original design - including the very distinctive top adjuster and screw in piece, where we have replicated the knurl and chamfers exactly as the 1940 originals - so they also look very pretty.  Kit is six pieces and will fit all Amal TT and RN carburettors and should also fit most later GP carbs).

AUG 2023: NOW BACK IN STOCK 

All parts are CNC manufactured with the same dimensions and profile as the originals, including the distinctive profile/knurl of the cable adjuster kit (3 parts) that screws into the top of the carburettor body - these were quite distinctive adjusters, with a flat top face above the knurl - only fitted to the racing carburettors.  Slide and and slide stop are in brass, but we manufacture the screw in top/adjuster and adjuster locknut in stainless steel - which looks nice and does not rust.

Our screw in top and adjuster locknut use the correct imperial Across Flats hex dimensions, so they fit correct imperial spanners.

Update April 2020:  These are now back in stock.  We are also offering the spring (Item 0850) and the top cable adjuster and locknut (Item 0871) as seperate items.  

Air Adjuster Mechanism - Background:

The air adjuster slide mechanism was fitted to all competition TT, RN (Remote Needle) and later GP carburettors.  There may have been very minor differences to the adjusters over the years (by batch) - but the distinctive overall shape and mechanism - as far as I am aware, remained unchanged. The final two diagrams are original period pictures of a TT carb body with air adjuster mechanism and a cutaway picture of the mechanism as it was fitted to later GP carbs.

The mechanism was not considered a 'Choke' in the way that other carburettors use a choke just for starting - instead it was described as an air adjuster, that would allow for slight richening of mixture by closing - for varying 'atmospheric conditions' or starting.

Because the cable adjuster often used to corrode and get stuck in the hex screw top - it is very common to find someone has loosened it with a pair of pliers(!) - which invariably crushes the original brass adjuster, or at the very least ruins the knurl.  This kit will help restore the original look, as well being less likely to crush in the future - as the cable adjuster is in a harder material. 

It also seemed to be common practice for the air adjuster mechanism to be removed back when these carburettors were being used in period.  Not entirely sure why this was - but I think it was possibly because if they inadvertently closed in a race (through engine vibration or whatever), it could affect carburation and possibly cost someone a race.  I remember when historic racing in the 1980's, it was common to remove this mechanism if fitted.  Because of this, these air adjuster mechanisms have always been hard to find - it is rare to find a second hand carburettor sold with this still in place - so this kit will help replace the full mechanism if missing.

Final point - the original Amal tuning guide for competition carburettors did suggest using this mechanism as an aide for setting up the carburettor - it helping to determine the correct slide cutaway required (as opening closing the slide will help richen the mixture slightly).  We sell a facsimile of the setup instructions in our catalog section. 

This is a cable adjuster and locknut with a 0.250" BSC thread, which is of the distinctive 'knurled' type that were originally fitted to Amal TT, RN and GP competition type Air Slides - however, they can also be used as throttle cable adjusters on other carb types - that had a similar thread, or a 1/4" through hole to take a similar adjuster. 

Price is per adjuster and nut.

These are CNC manufactured from stainless steel with the distinctive flat top face above the knurl - only fitted to the racing carburettors.  Locknut uses the correct imperial across flats dimension as the original (originals being used as the template for these).

This cable adjuster (and indeed the complete air adjuster mechanism) was often removed from Amal competition carbs in period.  If they are still in place it is very common for someone to have tried to unlock them with pliers - as the originals were plated brass - this almost always crushed the top cable recess or ruined the knurl.  Therefore, these adjusters with the correct profile are now very hard to find in good condtion - our adjusters are therefore a nice detail touch!  We sell the complete TT/RN/GP air slide kit - whiich includeds this threaded adjuster and locknut as Item 0149, however, some customers may already have the other parts - and as it is this adjuster that commonly gets 'mauled' most commonly, we also sell this adjuster and locknut seperately here.

Fitment to later TT Carbs and other carbs and Twistgrip Throttle Assemblies:

This particular type of adjuster was always fitted to the TT/RN (and GP) Air Slide cable top piece - it having a 0.250" BSC Thread.  Most earlier Amal TT and RN carburettors (approximately up to 1952) used a different (larger - 3/8" BSC thread) adjuster for the throttle cable and Top Cap - we also sell that item - Item 0874).

Later TT and GP carburettors often had a Top Cap to take a much slimmer throttle cable adjuster, similar to that used on the roadgoing Amal Monobloc and Concentric carburettors - that type was of lesser diameter than the adjuster shown here - but we sell that type of adjuster as well - Item 0149.

However, you may find that some Amal TT Top Caps have a 'through hole' - which may be of 0.250" diameter (I have seen numerous patterns fitted over the years to these carbs) - in whcih case this could be a suitable altenative.

Twistgrip Throttles: (i.e. genuine Doherty Type):   It should be noted that most genuine Doherty Twistgrips (including the modern genuine Doherty twistgrip we sell - Item 0942) did not have provision for a cable adjuster to be 'screwed in' to the handlebar casting - instead they had an 'unthreaded' hole - which might have had a ferrule or an adjuster dropped into that hole in period.  We manufacture a stainless steel 'Top Hat' Ferrule for this type of Doherty Twistgrip - see Item 1178, but as can be seen in the accompanyning photographs of both a genuine original Doherty quick action twistgrip, and a modern Doherty twistgrip (Item 0942) - the knurled adjuster and locknut offered here is also a viable alternative to be used with a throttle cable on the Doherty type twistgrips of that type - as the 0.250" diameter adjuster is a perfect 'drop fit' into the hole, and where the locknut is used to adjust the final tension of the cable (and being stainless steel, they are less likely to rust in the elements).

2 part throttle cable adjuster and locknut to fit original Amal TT and RN competition carburetters (with 3/8" diameter BSC thread), CNC manufactured in stainless steel, but with the same profile and distinctive knurl as the original competition item. 

Price is per Adjuster and Locknut

These are CNC manufactured from stainless steel with the distinctive flat top face above the knurl - only fitted to the earlier Amal TT and RN type racing carburettors (up until the early 1950's - later competition carbs being fitted with the more common monoblock road type).  Locknut uses the correct imperial across flats dimension as the original (originals being used as the template for these).

This cable adjuster was fitted mainly to the earlier (pre mid 50's at a guess) original Ama TT and RN carb tops.  Originally they were were manufactured in brass and dull nickel plated, and were fitted with 3/8" diameter BSC fine thread cable adjuster.  An original adjuster and locknut is shown in the second photograph alongside our version, and was used as a template.  However, because they were made in brass - they were often 'mauled' with pliers and it is now very rare to find this original and distinctive design still in good condition.

It should also be noted that this original type of threaded adjuster was also counterbored underneath to fit the early type straight throttle spring, as shown in the second photograph.  Our versions have the same counterbore.  We also sell both the parrallel type spring and the later conical type spring . . . bot types can be used with this adjuster if required.  

The original adjuster was in brass and very often seized in the carb top .  .. and then owners tried to remove them - invariably with a pair of pliers - so it is normal to find carbs missing these adjusters, or at least with the knurl chewed or crushed.  Our versions are CNC manufactured in stainless steel, so as well as looking nice, will be stronger than the brass originals.

Final point - later alloy top caps (probably mid 1950's onwards) were often fitted with smaller inner diameter alloy caps - and sometimes smaller adjusters, or no thread in them at all.  For this later type of cap - see the later adjuster we also offer - Item 0145, later in this section.

We CNC manufacture these in stainless steel to the original design so they do not rust and will add the final touch to your competition carb restoration - but although small they still require multiple machining ops (including the slim nut which requires a special 2nd op to remove scurf after parting), hence the price.

These are lovely quality chromed chamber cap to fit all original 10TT Amal Carburetters, CNC manufactured to the original design, with lovely crisp grooving (important not just for grip - but because many TT carbs use the later type design bellmouth spring (our item 0139) which uses this grooving to stop the top ring rotating.

These are CNC manufactured for us in the UK from brass, and then polished and chromed to a high finish (also in the UK - by a company specialising in classic vehicle plating and polishing).  Note also that as part of the manufacturing process for these caps - the ring grooves are not knurled, but are individually grooved on a CNC mill, to ensure a crisp and accurate finish - which knurling would not achieve (and explains why not a cheap part to manufacture).  Some owners of early original Amal racing carbs will know that original knurling is often damaged and worn - resulting in the cap being difficult to remove.

The type shown here is the type originally fitted to post-war TT carburettors, where the ring was secured using the retainer spring shown below (4/307) - and we also sell the similar quality inner cap that fits this ring - Item 0138.

Some pre-war TT carburettors used a slightly different design of chrome ring and inner cap - where the cap had a captive ball and square headed screw - by turning the screw clockwise, the ball came out and locked the ring.  Although an unusual design and original fitment pre-war, that type of cap made it very easy to damage the chrome ring - as most people forget to untighten the square head screw before undoing the chrome ring .. we recommend using this type in conjunction with the large bellmouth retained spring,

But if you do wish to retain that earlier type of inner cap (and still have an original) - you can still do this, but some of the earlier inner caps may have a different recess diameter - in which case you would need to machine out the inner diamteter of this cap slightly to accomodate - email us wiht dimensions of your original inner cap if you are not sure on sales@racingvincent.co.uk

Finally, if you own an Amal RN (Remote Needle Carburettor), that carburettor, although similar, uses a larger diameter top ring - which we can also supply - Item 1057.

Update November 2021 - We have just had a new batch of both these and the RN top rings come in, apologies the price has risen - but as you may be aware the price of brass has risen hugely in the last 18 months (post Covid impact?)

This is the turned aluminium choke top piece, that holds throttle cable adjuster on original Amal TT carburettors. These are CNC machined to a high standard and should fit onto any original Amal 10TT carb body. 

Comes complete with throttle cable adjusters and locknut

Price is each.

The threaded/knurled top ring then fits over this top piece and screws down onto the carb body - we also sell the correct style 10TT (and GP10) top ring - which is Item 0137 . . . as you can see from the photo they look very pretty together. 

This is the later TT carb design,  which used a leaf spring against the knurl to retain it - which we can also supply, that being item 0139.  Note we also sell the threaded cable adjuster and locknut seperately - item number 0145.

These mixing caps have an inner spigot diameter of 0.875" (although as at Dec 21, we are also in the process of manufacturing the similar looking Amal RN (Remote Needle) type with a larger diameter - if you wish to reserve one of these for an RN carb - email us at sales@racingvincent.co.uk

Notes on Original Amal TT and RN Top Piece Design:

It should be noted that earlier (particularly pre-war) Amal TT and RN carb design had a different type of choke top piece, made from brass and identifiable by a vertical square headed screw, next to the cable adjuster.  This type used the square headed screw to lock the brass knurled top ring in place - when it was tightened it pushed out a small ball from the side, that locked the ring in place.  Because it was very difficult to see if the square headed screw was tightened (or owners did not understand its purpose), these were often not loosened before trying to remove the top ring - therefore damaging and denting the top ring.  Therefore this later design simplified the top piece design, to prevent unnecessary damage - but if fitting this type - it requires a leaf spring (Item 0145) is fitted behind the bellmouth lockring to prevent the top ring moving.

The earlier design also used distinctive, wider diameter throttle adjusters - which we can provide, (Item 0874), which are very pretty and distinctive of those earlier TT/RN models - but remember you will need to bore and re-thread the top cap throttle cable hole to accomodate this earlier type.

These are lovely quality chromed chamber cap to fit all original 10RN (Remote Needle)  Amal Carburetters,  which were the carburettor type fitted to most competition/racing SOHC and early DOHC Norton's from the late 1930's through to the early 1950's.  Original Amal RN carbs are now very difficult to find spares for - and this is one of the parts specific to that carburettor type, and this ring is copied from an original pattern.

The RN top ring was of a slightly wider diameter than the more common Amal TT type (our Item no 0137), as well as being slightly less deep -as the top ring for this carb type also needed to retain the Remote Needle throttle needle cap and prayer book spring (which we can also supply - Item 0167), specific to the RN design.

They are CNC manufactured to the original pattern, with lovely crisp grooving (important not just for grip - but because many TT and RN carbs use the later type design bellmouth spring (our item 0139) which uses this grooving to stop the top ring rotating.

These are CNC manufactured for us in the UK from brass, and then polished and chromed to a high finish (also in the UK - by a company specialising in classic vehicle plating and polishing).  Note also that as part of the manufacturing process for these caps - the ring grooves are not knurled, but are individually grooved on a CNC mill, to ensure a crisp and accurate finish - which knurling would not achieve (and explains why not a cheap part to manufacture).  Some owners of early original Amal racing carbs will know that original knurling is often damaged and worn - resulting in the cap being difficult to remove.

The inner diameter of this ring is also slightly greater than the TT type - it being to fit the original Amal RN inner cap that had an inner spigot diameter of 1.062" (27.1mm)

Note November 2021:  Currently, we do not offer the original type Amal RN inner cap (i.e. with the 1.062" spigot, an original item is shown fitted in the accompanyning photos), but we will shortly be manufacturing a batch, similar to our TT type (Item 0138), but with the wider spigot.  Email us at sales@racingvincent.co.uk if you are missing this item.  Note also that the TT type 0138 will fit into the bore of an original RN10 carb - as the cap has a lip on its outer diameter that keeps it centralised .. . so can be used at a push if you do not have an original RN cap, and cannot wait for our RN type to be manufactured.

- This is the throttle cable adjuster and locknut as fitte d to many later roadgoing Amal carbs, however the thread size is 7/32 x 40tpi, and if fitting to a later Amal TT carb - you should check what thread type (if any) is already fitted - as some later Amal TT caps had different threads (or no threads at all, in which case a cable cap is often fitted - or the adjuster is stopped in place by the locknut on the adjuster alone).

Note - these are modern type adjusters from a UK manufacturer and will fit both Amal TT carbs as well as Monoblock/Concentric models.  They are high quality, but if fitting to replace the original early Amal TT/RN type threaded adjusters on original carb tops - they are slightly  slimmer diameter, so will require a small washer under the locknut, so as to give full purchase for the cable . 

Note also - if you have an earlier Amal TT or RN fitted with a brass top cap - these were normally fitted with a distinctive knurled top cable adjuster - particular for that model (normally 1930's to early 1950's TT/RN carbs) - we also manufacture that earlier and wider type of adjuster - See our Item 0874

These also fit the Amal TT type top alloy chamber tops (Item 0138) we manufacture - if you have previously bought one of these tops, which are threaded for this type of adjuster.

This listing is for a universal type throttle cable of 37^ in length, with nipples fitted either end - to fit most twistgrips and Amal carburettors.  This cable type has an adjuster in the middle of the cable (about 6" below the twistgrip). 

Price is Each.

This cable type comes with a small barrel type on one end (of the type that fits in all the twistgrips we sell), then a cable adjuster and locknut about 6" further along the cable (i.e. ideal for being adjusted when sat on the bike, just below the handlebars), and with a small cylinder ferrule at the other end - of the type that will fit most Amal throttle slides (including TT, RN and GP).

It should be pointed out though that if you are making cables up for competition TT, RN or GP carbs - and are intending to use our 'original type' air adjuster kits or throttle cable adjusters - that fit into the body of the carburettors - then you will need to unsolder the barrel at one end, carefully grind the cable to a point - so the barrel can be removed, then the outer cable adjusted to account for an new adjuster that is fitted.

We also sell a spare throttle cable outer cable ferrule, and inner cable barrel ferrule (i.e. the twistgrip end) as a seperate item - Item 1218, so if you are modifying the cable, and do not have a box of ferrules . . . you can fit a new outer cable ferrule if you have trimmed this cable to length, and fit a new inner cable barrel if the one that comes fitted is unusable (see Item 1218 for more information)

Although not listed - I should also be able to help with extra ferrules and cable barrels - and may be offering them in the near future (this update in January 2024). Also, if you email me on paul.norman@racingvincent.co.uk, I can provide more information on this cable setup process - it used to be a normal part of any 'Project Build' - making up all the cables to fit your particular motorcycle - but if you are doing this yourself for the first time - remember to 'tin' the cable before cutting or grinding it, and use plumbers solder rather than electrical solder.

This listing is for a universal type throttle cable of 37^ in length, with nipples fitted either end - to fit most twistgrips and Amal carburettors.  This is the 'plain' cable type - i.e. there is no adjuster fitted along the cable length.  

Price is Each.

This cable type is useful if you are fitting it to a carburettor or twistgrip that has its own cable adjuster already fitted.

In the case of twistgrips - some twistgrips come with a cable adjuster which is 'slotted' along its length - in this case, you may find the cable can be used just as it is (i.e. it comes with the ferrules either end already fitted, to fit most twistgrips and Amal throttle slides) - as the inner cable can be fed through the slot, without having to remove an inner cable ferrule to slide it on.

However, the main reason we list this type of cable, is for those customers who are fitting an Amal competition carburettor such as the Amal TT or Amal RN (for which we sell many parts, including - the original type cable adjusters particular to those models) - and want to fit cable adjusters particular to that carburettor type - either throttle cable, or air slide cable.  In this case - of course it will be necessary to heat one cable end up, to release one of the ferrules, and then feed the required adjuster on to the cable - and probably require the outer cable cutting to length, before re-soldering.  To do this it is expected you will be familiar on how to 'make up' cables yourself (i.e. tinning the inner cable, how to grind the end without fraying the strands etc) - but if you need help with this, you can email me at: paul.norman@racingvincent.co.uk.

We also sell a similar length throttle cable with a cable adjuster fitted midlength - this is Item 1216.  It should be noted though that that cable has a 'top hat' type outer cable ferrule on one end, which means it can be dropped into a carburettor top with no thread - while this cable type has a plain outer cable ferrule at both ends (i.e. it will just drop through a carburettor top, if the top was intended for a cable adjuster.

As a final note on this - if taking this route (i.e. removing the ferrule from one end to fit an adjuster etc) - we can also offer a useful small item -  Item 1218 - which consists of a spare throttle cable ferrule - of the type commonly fitted at the twistgrip end, and one outer cable ferrule, which can be fitted over the end of this outer cable, if you have trimmed it to a new length (I normally use a small sharp punch, to slightly punch the ferrule after fitting over the cable outer, to stop it coming off).

Also, if making up cables for yourself for the first time - remember to 'tin' the cable before cutting or grinding it (to help prevent the cable strands splaying), and use plumbers solder rather than electrical solder, as well as a good quality soldering flux.  and FYI - do not put any oil on the inner cable where you are intending to solder - they almost never 'tin' once impregnated wtih oil.

This listing is for a spare Throttle Cable (or choke/air/magneto type cable) outer cable ferrule, and a spare inner cable barrel of the type normally fitted on the twistgrip end of throttle cables. 

This item is useful if you have bought a throttle cable (see items 1216 and 1217) and need to then cut the cable to length or fit an adjuster.  

Normally to amend the length of a cable, or fit an adjuster, requires that the outer cable has to be trimmed to a new length - which loses the pressed on cable end ferrule that it comes with.  Therefore this spare outer cable ferrule can be placed over the newly trimmed outer cable to protect it.  When making up cables - I normally use a small sharp punch and give this ferrule a small punch midway along its length, to stop it slipping off in use.

Likewise, the inner cable barrel ferrule can be used to replace the twistgrip end ferrule, if the original is not re-usable after amending the cable.  But make sure you check this barrel type fits your twistgrip (or air/magneto lever, if being used for that purpose) before fitting!

You can email me on paul.norman@racingvincent.co.uk if you require more information about making up and soldering your own cables - or require other ferrule types, I may be stocking more types in the future.  Also - read the listings for Items 1216 and 1217 for more information.