Tech Tip: Amal Concentric Mixing Chamber Top Caps

Tech Tip: Amal Concentric Mixing Chamber Top Caps

Have you ever purchased a new set of Amal Premier carbs (or planning too) and noticed at the very top of the carb that there are adjusters for both throttle and choke cables?

Truth be told, new Amal Premier and non-Premier carbs have been coming to us this was since they introduced to the market

No it’s not to aggravate you when you try to install your cables only to find that your original cable set-up won’t work..

If you happen to be stuck in this situation, there is an easy, clean and correct way to proceed 

The easiest and quickest way (although crude) is to drill them out, or swap them with your original carb tops (if you have them).. but who wants to do that when you can have a genuine Amal part that as simple as removing one cap and installing an other?

Today we are going to showcase all the Amal top caps that where fitted to a wide variety of late model British motorcycles

Let’s begin..

What is an Amal mixing chamber cap?


Amal Carburetor Top Cap Removed

To be able to house and retain your throttle and choke cable return springs, Amal Concentric carburetors use a top cap that is secured by two screws

There are also two holes bored at the top of each cap to allow a throttle cable and choke (air) cable

The cap acts as a divider between the outer cable housing and springs making the opening and closing of your throttle or choke slides possible

Without a cap, your not going anywhere

Caps over the years

Since the introduction of the Amal Concentric carb in 1967, the Amal Concentric carb was fitted to hundreds of different make and models of motorcycles

This includes both two stroke and four models from Triumph to Bultaco

Since most of us that own vintage British motorcycles are not the original owners, this actually opens up the door to having incorrect parts on you’d bike as parts get swapped from owner to owner

Some models had chokes, some didn’t, some models also had “hat shaped” cable ends while many models had ferrule ends

This leads to confusion today, but let’s make it easy from here onward


Caps by Amal (current production)


600 & 900 Series Amal Mixing Chamber Caps


Whether you have an original Amal Concentric carb or a new Amal Concentric carb all Amal carb top caps available from Classic British Spares are interchangeable...

Keep in mind that the 600 and 900 series caps "look" the same, but they are different in terms of size

Our Amal caps will even work with our new Wassel Evo carbs..

Below we will show each cap and also explain to you the type of cable to in need to work that specific cap

Let’s take a look..


Cable end types & caps


 Throttle Cable End Types


Here is a hat shaped cable end and a ferrule cable end

Ferrule end cables are to be used with the proper cable adjuster that threads into the top cap..

Cap #1 928/064 & 622/064

 928/064 - 622/064 Mixing Chamber

The 928/064 & 622/064 cap features 2 threaded holes for adjusters to accept a ferrule type cable

This particular cap is the cap that comes with the new Amal Premier and standard concentric carbs including all 600 and 900 series carbs


Throttle Cable Bore Choke Cable Bore Cable End Type
Threaded Threaded Ferrule Type


You typically find this set-up on many late model BSA and Norton models..

Click here to purchase this cap for a 600 series carb and click for the 900 series carb


Cap #2 928/098 & 622/098

 928/098 - 622/098 Mixing Chamber


The 928/098 & 622/098 cap features (2) non-threaded holes to accept hat type ends on both your throttle and choke (air) cables 



Throttle Cable Bore  Choke Cable Bore Cable End Type
Non-Threaded Non-Threaded Hat Type


Click here to purchase this cap for a 600 series carb and click for the 900 series carb 

Cap #3 928/097 & 622/097

 928/097 - 622/097 Mixing Chamber

The 928/097 & 622/097 cap features a non-threaded hole for a throttle cable and a threaded hole for a choke (air) cable 



Throttle Cable Bore Choke Cable Bore Cable End Type
Non-Threaded Threaded Ferrule & Hat Type


This style of cap is popular on late model Triumph twins (and others)..


Click here to purchase this cap for a 600 series carb and click for the 900 series carb


Additional parts


4/137A Amal Choke Blanking Plug


Should you have a cap that has a hole that is threaded for a choke cable adjuster and you choose not to run a cable, you will need to plug the hole

Leaving the hole "unplugged" is an air leak and will allow water and debris to enter your throttle valve chamber 

Amal Concentric carb caps have a 2BA thread pitch and diameter which is a British thread form (not American or Metric)

We stock a genuine plug specifically for our caps as shown in the photo above

Click here to purchase your blanking plug today




Kyle of Classic British Spares has compiled a video in which he quickly goes over the differences should you fancy a video compared to reading..

Click the cover (image) above to watch the video now 


Thanks for reading


Thank you for taking the time to read today's Tech Tip post 

We hope that it may be of value to you

Should you have any questions, or if you would like to chime in, please leave us a comment in the section below

Ride safe! - Classic British Spares


  • Robert N Krauss

    Excellent video. Well composed and expertly presented. Thank you for leaving no questions unanswered.

  • Ed Cronin

    Very interesting Video, real helpful. I have Two 67 Triumph Bonniville’s one being a TT Special. Which I plan on putting two New Premier Carbs . Thx for the Information.

  • Classic British Spares

    @David – Thank you for reading and commenting today Dave!

  • Classic British Spares

    @Neil – Good! Glad you found it resourceful

  • Neil McCartney

    Thanks Guys I didn`t know this so it very useful information.

    Cheers !!

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