Listed here are reproduction parts to fit Amal Grand Prix 1 (GP) carburettors. These carburettors were fitted to DOHC Featherbed Manx Nortons. Although I specialise in SOHC Nortons, I do have a '55 double knocker, so when I replaced the slide of my GP5, I decided to get a couple extra and put them on the catalog. I have since sold almost as many as I have TT slides, so I will probably continue to build up the stock of GP parts as well. Ask me if you have a requirement for something not listed, I maybe able to help

Castrol ValveMaster Plus - Lead Replacement Plus Octane Booster - 250ml Bottle.  If your Norton (or any other classic motorcycle) has not been fitted with new 'unleaded' type valve seats, then using modern unleaded petrol will lead to excessive wear of your valve seats.

Castrol offer Valvemaster Plus to combat this problem - just add a small measure of this liquid to your fuel tank each time you fill up and you will effectively be changing your 'unleaded' specification to 'leaded type - and therefore will protect valve seats.  

Note: Castrol make 2 versions of this lead replacement additive, a standard version, and then this version which also has an Octane booster included.  I always add this version to my British motorcycles - as I want to provide as high as an octane rating as possible to the high performance engines we are running (SOHC Nortons, sports twins etc), to reduce the possibility of pinking.  Therefore I use this in all my classic bikes.

However, should any more encouragement be needed - it is also endorsed by the Federation of British Historic Vehicle Clubs.

This 250ml bottle will treat 250 litres of fuel (1ml to each litre of fuel).  The reason I like this Castrol lead replacement offering over other makes is that the bottle includes a clever measuring device at the top - just squeeze the lower part of the container until the correct quantity of the additive fills the top measuring holder, which is graduated with the different quantities of fuel you are filling your tank with - simple!

Always read instructions before use.

 

Driven Defender and Booster - Lead Replacement Plus Octane Booster - 295ml Bottle.  If your Norton (or any other classic motorcycle) has not been fitted with new 'unleaded' type valve seats, then using modern unleaded petrol will lead to excessive wear of your valve seats.

Driven is a well known specialist American oil company, producting oils and additives for the motor racing industry - and one of their products is this fuel additive that protects valve seats on older style 'leaded' engines, as well as increasing octane  - just add a small measure of this liquid to your fuel tank each time you fill up and you will effectively be changing your 'unleaded' specification to 'leaded type - and therefore will protect valve seats.  

This 295ml/10 Fl oz bottle will treat up to 25 gallons (not litres . . . remember it is a US company!) of fuel.  The bottle has graduations along its side, along with a clear plastic area so you can easily see how much additive you  are adding on each fill up. 

I have recently stocked this item because other UK additives have been getting harder to find - and it is supplied by my main racing fuel distributor, so know they can be trusted.  I am using this additive myself now in my roadgoing Vincent and will report back results later in 2018

Always read instructions before use.

This Facsimile is a full and comprehensive catalog, listing good quality reproductions of original Amal specification and tuning sheets for the Amal TT, RN (Remote Needle) and GP competition model carburettors, and also includes a full list of settings for SOHC Norton models when fitted with these models as well as a comprehensive setup guide from period Norton technical guides for these carburettors.  

Price is Each

We also include the most common TT/RN carb settings for Norton 350cc and 500cc carbs, as well as some other useful carb tuning information from period Norton and other tuning experts.

Background:

The TT type competition carburettorwas first produced in the 1920's - before Amal was formed, at that time the company was called Amac - and we include a single page exploded view of that early Amac design in this facsimile.  The carburettor was then updated through the years (some pre-war versions being identifiable as they had the sub-model number relating to year stamped on the flange - i.e. TT27 or TT35), before being developed into the RN (Remote Needle) carburettor - used mainly on genuine competition bikes only, such as Manx's and KTT's, before being further developed into the GP carburettor. 

We also include one of the first of the Amal TT specification sheets (on which the cover shows the amalgamation of Amacs, Binks and B&B to create Amal), from approximately 1934, which also lists and shows pictures of many of the other carb accessories they were making in the early 1930's.  This being from an original I have in my own collection 

This Facsimile brings together copies of many of the original (and rare to find) Amac/Amal Tuning/Spares sheets for these different carburettor types - and as well as giving an interesting chronological account of how they changed - is invaluable for anyone trying to setup these carburettors - as there is a very specific order to do this in for most of the designs.

Then, in the second half of the document we have a section listing the most common settings for TT and RN carbs fitted to Norton SOHC models by year, as well as some common settings for many bikes fitted with Amal competition carbs in the 1950's (from a well known tuning book at the time). 

Finally, we also include a section from one of the period (1940's-50's) Norton technical manuals, written by the then Technical Manager for Norton's - Edgar Franks, on how to setup your road Norton SOHC for TT carbs, as well as a section on racing.

As well as being an interesting Facsimile, it contains a wealth of information for anyone who has a bike fitted with either TT, RN or GP carbs.

Printed on high quality A4 paper, with original documents carefully reproduced (and cleaned up if necessary), with a green card cover and Contents section, this facsimile is of circa 50 pages in total. 

High quality throttle slide to fit original Amal 5GP Carburetter - as fitted to shortstroke 500cc DOHC Manx Norton's from approximately 1953/54 onwards, as well as many other competition and sports motorcycles from the mid 1950's onwards. 

These are UK manufactured to the original design and available in 3 commonly fitted cutaways - No3, No5 and No6 Cutaways.

For Reference, Shortstroke Manx Norton models most commonly used the following cutaways:

1953 onwards DOHC 500cc Manx Norton:  5GP No5 Cutaway Slide

1953 onwards DOHC 350cc Manx Norton:  5GP No4 or No5 Cutaway Slide

(note although we do not offer a No4 cutaway - the No3 is similar, and has the option to have its cutaway curve extended by 1/16" to convert it to a No4, should a customer wish to do so).  If setting up an engine for the first time, it is often useful to have slides of different cutaways, so that changing them as part of the setup process can allow for differences to be noted before settling on a final cutaway. 

Price is Each.  

Like the TT and RN slides we also offer, these GP5 slides are CNC manufactured in the UK from high quality Naval brass (far less likely to split than normal brass) and machine finished to a high standard, before finally having their outer face 'Finish Ground' to the correct tolerance. Like original slides, they then have a final thin coat of nickel plating (only a few microns thick) - which is cosmetic to prevent corrosion.

The GP5 slide carburettor was commonly fitted to DOHC shortstroke Manx Nortons from approximately 1953/54, and in one of the photographs you can see the similar slide fitted to the GP5 carburettor of my own 1955 500cc DOHC MAnx Norton.  

December 2021: New batch back in stock

 

Amal RN and GP carbs fitted to 1950's Norton Information:

FYI - Manx Norton models were fitted with the Amal 10RN (Remote Needle) competition carburettor from the late 1930's through until the early Longstroke Featherbed Manx Norton models, approximately 1951/52.  We can also supply throttle slides to fit original RN carbs - see our RN Section.

From approximately 1952 Manx Norton models were fitted with the Amal 10GP.  This had a smaller diameter throttle body than the 5GP.  Throttle slides for this carb type are now very uncommon to find.  As at Dec 2021 - we are hoping to have a small batch available of this slide in the next 3 months - email us on sales@racingvincent.co.uk if wishing to reserve one of these - stocks will be limited.

From approximately 1954-5 the DOHC Shortstroke Manx Norton was then fitted with the larger bodied Amal 5GP carb.

 

- This is the special needle clip fitted to GP carburettors - It also requires the special lockscrew which ensuresthe clip does not come loose - (RN Customers - Sorry, although it looks close, this clip will still not work for RN carbs, I tried!)

Correct type conical throttle spring to fit Amal TT. RN and GP type racing Carburettor's

This type of conical spring were fitted to all the Amal racing carburettors - i.e. TT, RN and GP types.  These are manufactured in the UK and are just as per original. The smaller end is placed on the throttle slide and the wider conical end fits at the top stop the spring moving over to one side. 

 

This is a throttle needle to fit original Amal Type 10GP and the smaller 15GP Racing Type carburettors. This is the 'Normal' type needle, but we can also supply the alternate 'Weak' type (identified by a '6' after the number) - for that, see Item 1141.

Price is Each

Note - these needes are UK manufactured by a specialist carburettor engineer, to the original Amal needle dimensions.  As per originals, they are stamped with the GP model and type designate (as GP needles were specific to the GP size type and were available in two types - 'Normal' or 'Weak').

Because these needles have been manfuactured over a period of years - occasionally there may be tarnish marks from being kept together in storage . . . but this will not affect their use.

  

Background for GP Carbs:

The GP carburettor was introduced in the early 1950's and was available in a number of different body sizes (i.e. the diameter of the throttle slide) - as the size of the throttle slide bore increased, the numbering of the GP carb model number decreased - i.e. 15GP was the smallest size (comparable to the 15TT carb, and actually quite rare to find), 10GP (comparable to 10TT carbs, and fitted to the later Longstroke Featherbed Manx Nortons - I think 1952-53?), then 5GP, then 3GP.  The range of inlet tract bore sizes for these GP variants is shown below:

15GP Carb:     7/8" To 1 & 1/16"

10GP Carb:     1 & 1/16" To 1 & 7/32" (Replaced the RN carb on late Longstroke Manx Nortons @1952/53)

5GP Carb:     1 & 7/32" To 1 & 3/8"   (Used on most short stroke DOHC Manx Nortons)

3GP Carb:     1 & 3/8" To 1 & 1/2"

The accompanyning photograph shows a line up of 4 racing carb types - a 10TT, 10GP, 5GP and 3 GP, to show the different carb type bodies - with the model this needle is to fit ringed in RED.

The GP carburettor design was an improvement on the earlier TT and RN carb design, in that it had the needle to one side of the throttle body, and fuel enters the choke through a spray tube inclined to one side, rather than from directly underneath as on earlier designs - giving the shortest flow.

To go with this, and to give a more sensitive tuning control - each GP carburettor type had two types of throttle needle available, with a different taper - the 'Normal' type was identified by just having the model type stamped on it - i.e 'GP', or the 'Weak' type which was identified by having a '6' after the model number, i.e. 'GP6'.

Both the 15GP and the 10 GP used a needle stamped just 'GP' or 'GP6', while later 5GP and 3GP type carbs had a needle with that number on it (and a corresponding Weak needle followed by a 6 after the number).

A good starting point when setting up a carb is to look at which of the two needle types was originally fitted for your model - but as so many factors can vary the performance of an individual engine (i.e. fuel used/atmospheric conditions/condition and tuning of engine) - it is often prudent to obtain one of each type of needle and satisfy yourself which runs best (using the original Amal GP setting up instructions).

 

This is a throttle needle to fit original Amal Type 10GP and the smaller 15GP Racing Type carburettors. This is the 'Weak'' type needle (identified by a '6' after the number), but we can also supply the alternate 'Normal' type - See listing for more detail - for that, see Item 1140.

Price is Each

Note - these needes are UK manufactured by a specialist carburettor engineer, to the original Amal needle dimensions.  As per originals, they are stamped with the GP model and type designate (as GP needles were specific to the GP size type and were available in two types - 'Normal' or 'Weak').

Because these needles have been manfuactured over a period of years - occasionally there may be tarnish marks from being kept together in storage . . . but this will not affect their use.

  

Background for GP Carbs:

The GP carburettor was introduced in the early 1950's and was available in a number of different body sizes (i.e. the diameter of the throttle slide) - as the size of the throttle slide bore increased, the numbering of the GP carb model number decreased - i.e. 15GP was the smallest size (comparable to the 15TT carb, and actually quite rare to find), 10GP (comparable to 10TT carbs, and fitted to the later Longstroke Featherbed Manx Nortons - I think 1952-53?), then 5GP, then 3GP.  The range of inlet tract bore sizes for these GP variants is shown below:

15GP Carb:     7/8" To 1 & 1/16"

10GP Carb:     1 & 1/16" To 1 & 7/32" (Replaced the RN carb on late Longstroke Manx Nortons @1952/53)

5GP Carb:     1 & 7/32" To 1 & 3/8"   (Used on most short stroke DOHC Manx Nortons)

3GP Carb:     1 & 3/8" To 1 & 1/2"

The accompanyning photograph shows a line up of 4 racing carb types - a 10TT, 10GP, 5GP and 3 GP, to show the different carb type bodies - with the model this needle is to fit ringed in RED.

The GP carburettor design was an improvement on the earlier TT and RN carb design, in that it had the needle to one side of the throttle body, and fuel enters the choke through a spray tube inclined to one side, rather than from directly underneath as on earlier designs - giving the shortest flow.

To go with this, and to give a more sensitive tuning control - each GP carburettor type had two types of throttle needle available, with a different taper - the 'Normal' type was identified by just having the model type stamped on it - i.e 'GP', or the 'Weak' type which was identified by having a '6' after the model number, i.e. 'GP6'.

Both the 15GP and the 10 GP used a needle stamped just 'GP' or 'GP6', while later 5GP and 3GP type carbs had a needle with that number on it (and a corresponding Weak needle followed by a 6 after the number).

A good starting point when setting up a carb is to look at which of the two needle types was originally fitted for your model - but as so many factors can vary the performance of an individual engine (i.e. fuel used/atmospheric conditions/condition and tuning of engine) - it is often prudent to obtain one of each type of needle and satisfy yourself which runs best (using the original Amal GP setting up instructions).

 

This is a throttle needle to fit original Amal Type 5GP Racing Type carburettors. This is the 'Normal' type needle, but we can also supply the alternate 'Weak' type (identified by a '6' after the number) - for that, see Item 1143.

Price is Each

Note - these needes are UK manufactured by a specialist carburettor engineer, to the original Amal needle dimensions.  As per originals, they are stamped with the GP model and type designate (as GP needles were specific to the GP size type and were available in two types - 'Normal' or 'Weak').

This model - the 5GP type carburettor were normally fitted to Shortstroke DOHC Featherbed Manx models, my own 1955 DOHC Manx has a 5GP fitted.  

Background for GP Carbs:

The GP carburettor was introduced in the early 1950's and was available in a number of different body sizes (i.e. the diameter of the throttle slide) - as the size of the throttle slide bore increased, the numbering of the GP carb model number decreased - i.e. 15GP was the smallest size (comparable to the 15TT carb, and actually quite rare to find), 10GP (comparable to 10TT carbs, and fitted to the later Longstroke Featherbed Manx Nortons - I think 1952-53?), then 5GP, then 3GP.  The range of inlet tract bore sizes for these GP variants is shown below:

15GP Carb:     7/8" To 1 & 1/16"

10GP Carb:     1 & 1/16" To 1 & 7/32" (Replaced the RN carb on late Longstroke Manx Nortons @1952/53)

5GP Carb:     1 & 7/32" To 1 & 3/8"   (Used on most short stroke DOHC Manx Nortons)

3GP Carb:     1 & 3/8" To 1 & 1/2"

The accompanyning photograph shows a line up of 4 racing carb types - a 10TT, 10GP, 5GP and 3 GP, to show the different carb type bodies - with the model this needle is to fit ringed in RED.

The GP carburettor design was an improvement on the earlier TT and RN carb design, in that it had the needle to one side of the throttle body, and fuel enters the choke through a spray tube inclined to one side, rather than from directly underneath as on earlier designs - giving the shortest flow.

To go with this, and to give a more sensitive tuning control - each GP carburettor type had two types of throttle needle available, with a different taper - the 'Normal' type was identified by just having the model type stamped on it - i.e 'GP', or the 'Weak' type which was identified by having a '6' after the model number, i.e. 'GP6'.

Both the 15GP and the 10 GP used a needle stamped just 'GP' or 'GP6', while later 5GP and 3GP type carbs had a needle with that number on it (and a corresponding Weak needle followed by a 6 after the number).

A good starting point when setting up a carb is to look at which of the two needle types was originally fitted for your model - but as so many factors can vary the performance of an individual engine (i.e. fuel used/atmospheric conditions/condition and tuning of engine) - it is often prudent to obtain one of each type of needle and satisfy yourself which runs best (using the original Amal GP setting up instructions).