Author Topic: B40 star best set up for wrong carburetor  (Read 1053 times)

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hoogerbooger

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B40 star best set up for wrong carburetor
« on: 12 November, 2017, 18:55:53 »
My 1965 B40 has a Amal 627 (428) concentric carb. 20 years ago Dave Smith of BSAOC said its from a Trident but is ok and recommended the set up as:

Main Jet: 140
Pilot jet: 20
Slide 3
Needle position 2
Needle jet .106

( I don't actually know how its set up)

I notice that the concentric that was fitted on some later B40's was a 626. So was Dave Smith right that my 627 as set up above should be fine. ?

I am presuming after 18 years of doing nothing in a garage I'll probably need to check/clean/service it. I did take it apart once but only checked if for crud & cleaned jets ( oh yes then had to emery the flange flat that my make over tightened).

I will see if I can the bike going, but would be useful to know if the 627 should be ok.

Ta



JulianS

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Re: B40 star best set up for wrong carburetor
« Reply #1 on: 12 November, 2017, 19:18:01 »
Your bike would have had a 1 1/16 inch monobloc, about 27 mm bore. The 627 is also 27 mm bore.

Condition is important.

Lots of information on the Amal website including rebuilding the Mk1 concentric, see link;

http://amalcarb.co.uk/rebuilding-mark-1-concentric-carburetter


Also see the tuning guide,

http://amalcarb.co.uk/downloadfiles/amal/Mk1_Hints_and_Tips.pdf

You should find all the information you need and you will be getting it from the manufacturer.

hoogerbooger

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Re: B40 star best set up for wrong carburetor
« Reply #2 on: 28 January, 2018, 17:25:04 »
The 627 concentric has no air slide ( or at least the one I have doesn't). Previously I bodged a choke for start up with a perforated cap -  I had no air filter attached- just removed cap when warm.

Is there any off the shelf or tidy bodge to fit an air filter with a choke ability ? 

[I could just buy the  the right carb and an air lever/cable, but if I can reuse what I have i'd prefer to  if there is a sensible fix ?]

 


JulianS

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Re: B40 star best set up for wrong carburetor
« Reply #3 on: 28 January, 2018, 17:37:16 »
Often bikes will start with just a good tickle of the carb and without a choke. Have you tried this?

But if you want a choke why bodge it, why not just fit a choke slide, cable and lever to your exsting carb.

AWJDThumper

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Re: B40 star best set up for wrong carburetor
« Reply #4 on: 28 January, 2018, 17:46:20 »
It will be interesting to see how your concentric carb set up compares with that of Phil C in the other B40 post!

hoogerbooger

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Re: B40 star best set up for wrong carburetor
« Reply #5 on: 28 January, 2018, 19:34:42 »
Tickling: even with the perforated cap on it wouldn't start easily in the cold.... unless I warmed it with the hot air gun !

Air Slide: Can't remember if internals allowed for an air slide ...... should it ? ( I'll have a look) but the cap has no hole for a air cable. So may be a case of take apart check for wear  & if barrel ok order parts worn or missing ?

hoogerbooger

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Re: B40 star best set up for wrong carburetor
« Reply #6 on: 04 February, 2018, 11:07:02 »
I've taken my carb apart to check how its set up & it's not as Dave Smith had recommended. The carb doesn't seem that worn. Some light lines on barrel and slide but only one I can feel with the finger nail. Slide seems a snug fit to the barrel and hardly any no lateral  movement.

Q1: Dumb question :  Are all 626 slides the same diameter ? Having stared at diagrams and looked at  spare parts on-line I still can't work out if the choke size is the bore of the carb barrel/ slide diameter ? Slides are listed as 626 slides without choke size. On mine the barrel diameter as far as my bad eyes and ruler measure is more than  27mm.

Q2: Dumb question:  Is the spray tube changeable or not? cos I have a Norton with the square bite out of it !

Q3: less dumb question: I'm thinking it may be sensible just to get a new 626 premium carb more guaranteed  function, fuel effeciency & resistance to modern fuel. I've provided the set-up as apparently fitted to the Australian WD B40s . I'm not sure if this set-up is best for my Star as i.e I haven't managed to find out whether the air filter used on the WD then or the fuel octane may have affected the set-up ? Anyone know whether they used a gauze air filter similar to the B40 star?.  Any one clever enough to tell me what the best ( starting) set-up would be for a 626 for a) an original gauze filter b) paper filter ?

 !!! this was a nice table table in word:

Dave Smith Recommedation   What I have 627/428      Amal Website -1967 Australian WD B40

Choke size         27mm               27mm                       26mm
Main Jet            140                   140                           130
Pilot Jet             20                     20                             20
Needle Position  3            1? ( i's on the top ring)          2
Throttle Slide     3                       3.5                            3
needle                            U ( no other markings/rings)
Needle jet          0.106                0.106                          0.106
Spray tube                                 Norton                        ? 4 stroke presumably

p.s. Also No O-ring or O-ring grove on flange of my 627






AWJDThumper

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Re: B40 star best set up for wrong carburetor
« Reply #7 on: 07 February, 2018, 19:11:38 »
Here are some answers to your questions:

Q1. All 626 slides are the same diameter - it's just the cutaway that different. The carb's choke size is the diameter of the bore running from the air filter into the cylinder head.

Q2. You need to use the correct spray tube for your engine - in your case, with a square end that is not angled.

Q3. The B40WD uses a paper element filter a bit like a B50 which is more constricting that the simple filter set up on a B40. The army specified the bike so that it could cope with harsh conditions, especially dust - hence the much more effective air filter.

hoogerbooger

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Re: B40 star best set up for wrong carburetor
« Reply #8 on: 08 February, 2018, 18:30:09 »
Many Thanks. New Carb needed then.

AWJDThumper

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Re: B40 star best set up for wrong carburetor
« Reply #9 on: 08 February, 2018, 19:46:39 »
The only real thing that wears out on an Amal carb is the throttle slide and bore, and the needle and needle jet. If the slide still seems to be a fairly snug fit then the carb may be ok. However, it might be worth replacing the needle and needle jet because it's difficult to know when they are worn out but, after 50 years, they might be. The slight differences in carb settings listed in your table including the choke sizes won't make a huge difference to the way the bike runs or starts although it's best to start with the needle position near the middle. The same is true as to whether you have an air filter fitted or not. In general, the standard B40 is a mild mannered beast and should start reasonably easily after tickling the carb. If the carb turns out to be ok then poor starting might be down to another issue with the engine (ignition timing, compression, etc).

hoogerbooger

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Re: B40 star best set up for wrong carburetor
« Reply #10 on: 13 February, 2018, 22:19:59 »
Can I double check. Are you saying the Norton spray tube and the 3.5 throttle slide won't make much difference and it should be possible to set up? (They being the main reason I was thinking a new carb was needed)

( I note your comments about needle and jets. cheap enough just to change.)

AWJDThumper

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Re: B40 star best set up for wrong carburetor
« Reply #11 on: 13 February, 2018, 23:01:33 »
I was really referring to the difficulties you have in starting the bike referred to in your original post which mainly depends on the pilot jet and the pilot airways. The slight differences in the settings in your table will affect how well the bike runs and particular how much power it produces but it won't affect how well or how badly the bike starts. For example, the slightly bigger cutaway will affect how smoothly the engine picks up from idling and, if not correctly chosen, might cause a slight hesitation or lumpiness. A slightly non-optimum main jet or less than ideal choke size or lack of air filter will almost certainly result a reduction in power (20-30%) in the produced. So, if you're having difficulty in starting the bike, it's the pilot jet system that will be the thing to worry about.

hoogerbooger

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Re: B40 star best set up for wrong carburetor
« Reply #12 on: 02 June, 2018, 17:13:40 »
my new 4 stroke needle from draganfly ( code 622/124) is very different to the one I've taken off.

new needle is 67mm long . old needle is 58mm.

( old need has a flat top and a "U" marked on it. New needle has chamfered top and two fine rings as markings)

More importantly, when the taper is compared from the top the old needle tapers earlier and seemingly more suddenly to a narrower diameter.

Very confused & can't see how they would do the same job.  Mix must be very different.

The carb is a 627 mark 1 concentric ( annoyingly with a Norton spray tube not the 4 stroke one) It's also got a 3.5 slide rather than the 3 that would be the later B40's that had a concentric

So do I fit the new needle ? and just see if I can get it tuned ?

Is the old needle one for "sportier" acceleration of a Norton ?

( old one looks smooth and untarnished. I replaced the needle jet, but it didn't looked clean and not obviously worn)
 


AWJDThumper

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Re: B40 star best set up for wrong carburetor
« Reply #13 on: 02 June, 2018, 17:38:25 »
The carb is not the one from the B40 (or a Trident as far as I can see) and therefore, unless someone else has determined the correct settings for it, you'll need to tune it. There is actually a choice of two needles for the 627: 622/124 which is 2 "V" grooves and 622/278 which is 5 "V" grooves. I'm not sure of the difference but will try to find out. It's possible the original needle was completely wrong for the carb.

JulianS

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Re: B40 star best set up for wrong carburetor
« Reply #14 on: 02 June, 2018, 18:11:50 »
Your carb was set up with pre 1969 parts. Then the carb was improved and the needle, needle jet and jet holder were changed. The needle went from 5.79cm to 6.74, the jet went from 1.74cm to 2.06cm and gained a cross drilling and the jet holder went from 1.9cm to 2.2.

You cannot interchange the parts you need a jet and jet holder to go with your new needle. The pre 1969 parts are obsolete.

See this link from Amal which explains all.

http://amalcarb.co.uk/rebuilding-mark-1-concentric-carburetter