Author Topic: Needle - which groove?  (Read 410 times)

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Phil C

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Needle - which groove?
« on: 06 November, 2021, 18:43:49 »
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

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Re: Needle - which groove?
« Reply #1 on: 06 November, 2021, 22:05:08 »
Hi Phil,

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

Dave.

Phil C

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Re: Needle - which groove?
« Reply #2 on: 06 November, 2021, 22:40:13 »
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

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Re: Needle - which groove?
« Reply #3 on: 07 November, 2021, 07:32:40 »
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

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Re: Needle - which groove?
« Reply #4 on: 07 November, 2021, 07:57:28 »
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

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Re: Needle - which groove?
« Reply #5 on: 07 November, 2021, 08:39:06 »
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

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Re: Needle - which groove?
« Reply #6 on: 07 November, 2021, 11:30:51 »
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

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Re: Needle - which groove?
« Reply #7 on: 07 November, 2021, 11:37:55 »
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

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Re: Needle - which groove?
« Reply #8 on: 07 November, 2021, 11:59:03 »
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? Iíve got an old monobloc from a B40 which is a little worn but works fine if you wanted to try another carburettor.

Phil C

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Re: Needle - which groove?
« Reply #9 on: 07 November, 2021, 12:58:08 »
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

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Re: Needle - which groove?
« Reply #10 on: 07 November, 2021, 18:20:27 »
Iím 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 Iíll sort out a monobloc for you to try!

Phil C

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Re: Needle - which groove?
« Reply #11 on: 07 November, 2021, 19:21:13 »
Thanks very much.