G80S Throttle valve size

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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Jackson
Posts: 48
Joined: Mon Jan 01, 1996 12:00 am
Location: ENGLAND UK

G80S Throttle valve size

Post by Jackson »

Can anyone confirm the correct throttle slide size for my 500 G80S engine.
Carb type 389/1, pilot jet 30, main jet 260
engine number 28139

Should the throttle be 389/3 or 389/3.5?
Will I know the difference!!

Manuals say different sizes:-
AJS manual 389/3
Book of AMC 389/3.5 (After eng 27000
376/3 before 27000)
Fred Neil '55 389/3
'56 389/3.5

Graham grjackson@btinternet.com
Rohan B.
Posts: 136
Joined: Wed Oct 12, 2005 10:45 pm
Location: AUSTRALIA

G80S Throttle valve size

Post by Rohan B. »

The difference will be that with a slide with 3/16" cutaway, it was running a shade rich coming off idle, and hesitate a little. So they increased the cutaway to 3.5/16". That is a very fine distinction !!

If you have a 3, be worth trying on modern petrol to see how it goes. If you are buying a new one, may still be best to go with the 3 - you can always file a bit off later on..

hopethishelps,
Rohan.
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TommoT
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Posts: 1602
Joined: Mon Jan 01, 1990 12:00 am
Location: DENMARK

G80S Throttle valve size

Post by TommoT »

Yes it cold potentially make a big difference. A change from a #3 to a #3½ slide transformed my engine (-56 G80S). Went from lumpy running and fouled plugs to smooth running and only occasionally fouled plugs!

Good luck!

Tom M. (TM)
TommoT

Ride Your Motorcycle As If Your Life Depended On It - Cos' It Does!
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