concentric mk1/premier - choke fitting & subsequent removal

[hoogerbooger]

Currently I have no choke/ air-slide fitted. I can't imagine doing much riding in cold weather so the ticker will probably suffice for cold starting on my B40 Star,  but:

After staring at my old throttle slide (pic attached) and a diagram of a concentric ,it appears you need to remove /knock out the closed section at the bottom of the air slide section, so that the slide can actually extend out into the air path and regulate air supply. How is this best done ? Or are there separate throttle slides with an opening ?

Once this is done can you go backwards and remove the choke apparatus. I can see there are blanking screws for the carb cap but will the opening in the throttle slide /choke air slide section then mess with with airflow/mix  ?

(If so filling the opening  subsequently would need to avoid risk of the filling falling out and getting into the engine - so presuming a new throttle slide would be needed ?)

[AdrianS]

There should be a cut out that matches the cross section of the choke air slide at the other end of the throttle slide.
The choke air slide has a spring and tube going through it and is all retained by the choke cable end nipple.

If you want to add a choke ( my B40 needs some choke to start when the weather is cold ), you will need a new throttle slide, air slide, brass tube and spring, together with a choke cable and choke lever. Also make sure your carburettor top has access for the choke cable.

[hoogerbooger]

FOR INFO

I emailed Amal on this who confirmed that having the air slide not fitted has some effect. They said:

"Trials riders like to block the air slide opening in the slide as it slightly improves the initial pick up from idling. On road bikes the effect is probably not noticeable."

& on whether they make Mk1 throttle slides with the opening closed they said that:

"We sell slides without the choke aperture open for the Mk 1.5 carburetters which had a different type of choke arrangement. They are only available in Mazak and not in the Hard Anodised form".

I think they means they would also fit a MK1. concentric, if  it was intended not to fit the choke parts.

So sounds like it is not a big issue for running my B40 Star, but worth knowing in-case there is a bit of hesitancy in pick up from idle.

(I found some references on-line to trail-riders filling the air slide void with silicone mastic......but I have no idea how well that would cope with fuel & heat, so am not vouching for this as a sensible idea).

[AdrianS]

Not sure what carb you are running?
My B40 has a monobloc with air slide and all functions perfectly. In fact I do need the choke to get the bike to start easily when the weather is cold and wouldn't consider running one without a choke.

[hoogerbooger]

Noted, and thanks for your comments. Bike was bought with concentric mk1 627 fitted, with no choke. Despite lots of tinkering and replacing of parts still doesn't run well. Still possible my problems are not with the carb, but am probably going to get a Premier to replace it. ( Certainly I've run out of things to check/clean/ or change on the current carb!)

After a bit of pondering I think I will fit the choke. I'd seen a few comments about the air lever loosening/failing/choke jamming on and was wondering, do I really need it & if I did have any problems, how much would I have to change to remove the choke subsequently.

Shall now just have to get on with it and see (as soon as my dodgy operated-on  foot is up to it)

[AdrianS]

You could buy a new monobloc ( expensive I know) which should sort the carb problem out. I bought one from Hitchcock. Very helpful too. Give them a ring, they may be able to help you if you want to retain your existing carb.

[Beesy]

Was going to add about making sure the cap had two cable holes in it. But see it's already been mentioned.