Needle - which groove?

[Phil C]

Evening all,

You might have noticed, I'm fiddling around with my carburretor (!)

Does anybody know please which of the three grooves in the needle I should fit the clip to? (Stupidly dislodged it when taking the carb to bits, before I saw which groove it had been in.) I believe they are normally numbered 1 to 3, with 1 being the top one.

The bike is a 1965 B40F, and the carb is a Concentric  (626  L301).

Thanks.     

Phil

[DAVE BRADY]

Hi Phil,

I believe that you have a workshop manual and an RR manual.  What is the recommended position in stated?

Dave.

[Phil C]

Yes I do have the books you mention, Dave, but RR doesn't give carburetion figures for a 1965 B40, and the Haynes lists it as Monobloc. So it seems to me I can't really use them. Phil

[chaz]

probably trial and error, the one Ive got is middle ring but then its got a larger main jet 200 against 160 normal but standard 106 needle jetn and no choke.
obviously, getting on for 50 years old , if original, needle and jets may be worn. Has any internals been changed?

[DAVE BRADY]

Good morning,

There is a previous thread on the Forum titled "B40 star best set up for wrong carburetor".
Some details about concentric on B40.  Looks like it could be useful and worth saving.

Dave.

 

[JulianS]

I suggest clip in middle groove and to start with set the air screw about 1 1/2 turns open from fully closed and be prepared to experiment with settings to get the best running.

If on points ignition rather than electronic I would check that the advance unit is working smoothly and not sticking.

[Phil C]

Any particular reason you mention the advance unit, Julian? Would a problem there fit with my bike's symptoms of conking out immediately after starting?  I remember ages ago when fitting a new points unit the advance mechanism seemed a bit sluggish but as the bike was working okay I didn't replace it. Phil

[Phil C]

Good morning,

There is a previous thread on the Forum titled "B40 star best set up for wrong carburetor".

Thanks Dave. Looked at that but still not sure whether to start on groove 2 or 3.  Decisions decisions...         Phil
Some details about concentric on B40.  Looks like it could be useful and worth saving.

Dave.

[AdrianS]

The advance unit failure would stop the bike from running. If seized in the closed position the timing would not advance when the revs increase . If the springs fail and you set the timing at the most regarded position, I suspect you might get a bit of a kick from the engine when starting!

Phil, where are you based? I’ve got an old monobloc from a B40 which is a little worn but works fine if you wanted to try another carburettor.

[Phil C]

Very kind of you to offer, Adrian. I'm in SW Devon. Where are you?  But I'll see what happens when I refit the carb (maybe tomorrow.) Fingers crossed, all might be okay then.   Phil

[AdrianS]

I’m not near south west Devon but we can always try the post if necessary!
If you get really stuck with no luck pm me and I’ll sort out a monobloc for you to try!

[Phil C]

Thanks very much.