Setup for MK1 concentric carbs

[triman65]

I have a 1973 Bonneville with concentric carbs and in the haynes manual it lists the two adjusting screws as pilot jet screw and throttle stop screw. There is no mention of an air mixture screw. so I suppose that the air mixture must be the pilot jet screw.

1 is this screwed in or out for more air

2 would the screw extend further out past the end of the casting

The plugs are new and the recommended number eg NGK 88ES
They are sooting up as the mixture is to rich and no sign of it being oil related. :-? :-?

[L.A.B.]

There is no mention of an air mixture screw. so I suppose that the air mixture must be the pilot jet screw.

 Actually it's known as the "pilot air screw". And it is the horizontal one of the two screws.

is this screwed in or out for more air

IN = richer, OUT = weaker (as it meters air, not fuel, as it's name suggests)

would the screw extend further out past the end of the casting

The normal range of the pilot air screw would be between 1 and 2.5 turns out from fully screwed in. If you find you need to adjust it further out than that to get an even idle, then there's probably something wrong somewhere?

The plugs are new and the recommended number eg NGK 88ES
They are sooting up as the mixture is to rich and no sign of it being oil related

Are you actually experiencing any running problems? As modern unleaded fuel seems to soot plugs even when the mixture is correct.

I suggest you get hold of a copy of the factory manual, as the Haynes manual isn't much good for the OIF models.

[Goldie]

When i adjust the pilot air screw on my twin carb Triumph pre-unit 750 motor, i get the motor warm and then disconnect one spark plug so its running on one cylinder. I then adjust the air screw in until the engine starts to hunt and run lumpy, and then turning it out. The engine should pick up speed as you are turning the screw out, but will start to cut out if you go to far. I normally set the air screw at the fastest tick over speed the engine feels comfortable at.
I then do the same procedure to the other carb.
When both carbs have been correctly adjusted by the pilot air screw, you will find that the tick over speed will most probably be too fast when you connect to other spark plug lead for normal running. You will then have to screw out the throttle stop screws equally to obtain the correct tick over speed.
Before you carry out any of the above, make sure that the throttle slides are both lifting together from the fully closed position, by adjusting them by the throttle cable. If you don't all the above will be in vain.
Hope this helps
Its quite simple really. Remember both slides should lift together, and shut down together, and that there should be the same turns on both throttle stop screws when lifting or dropping the slides.

[thunderbird]

thats exactly how i do it goldie [smiley=thumbsup.gif]

[triman65]

Thanks for the advice friends. I am in the process of changing all the Jets and needles and hope this cures the problem

Mick

[L.A.B.]

You may find this info useful?:

http://www.jba.bc.ca/Bushmans%20Carb%20Tuning.html (link was incorrect - now OK)

http://www.hitchcocksmotorcycles.com/amal/mk1_conc_ht.html

http://www.amalcarb.co.uk/