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.
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