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
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.
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 ?]
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.
It will be interesting to see how your concentric carb set up compares with that of Phil C in the other B40 post!
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 ?
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
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.
Many Thanks. New Carb needed then.
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).
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.)
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.
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)
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.
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
I think the needle you've got is the correct one - the other one seems to have been specifically used on a Trident (with a 626 carb).
Mulling over Julian's comment I think I'll put the old needle and needle jet back in as at least I knew I could get it running on that before, even if it didn't run that well.
If I get it running and MOT'd then I think I'll buy a new Concentric 626. and use the set up for the 1967 Australian WD B40 below ......but I guess with a 140 main jet as I'll be using the gauze air filter rather than the paper one that used. Does sound the appropriate adjustment for the air filter ?
( anyone ever seen half depth 5/16 CEI/BSC nyloc nuts ? as the ones I sourced for the carb studs are 11mm deep which is just too deep to squeeze into the gap with a spring washer between tickler & carb flange.........I guess I have to try filing them down)
Hello Hoogerbooger, AWJDT says below that it would be interesting to see how your carb compares with mine. I'm afraid I can't help at this stage, but thought I'd just send this post so you don't think I'm ignoring your issue. As you know, I have a 1965 B40F. It has a 626 carb, but I don't know the settings because I've not needed to take it apart after all yet (it started first kick the other day so I'm not inclined to tempt fate at the moment!) I did at one stage a while ago think I would take it apart but the problem was elsewhere (as I recall, me not knowing which way on the choke lever was open and which way was closed, until I took the air filter off and peeped in the carb intake!) I'm interested to read in this topic that some B40s had concentric carbs from new - I thought they were all monoblocs. I expect I'll have mine apart sooner or later, and will be on this forum asking lots of dumb questions. Phil.
Quote from: hoogerbooger on 03 Jun, 2018, 15:59
Mulling over Julian's comment I think I'll put the old needle and needle jet back in as at least I knew I could get it running on that before, even if it didn't run that well.
If I get it running and MOT'd then I think I'll buy a new Concentric 626. and use the set up for the 1967 Australian WD B40 below ......but I guess with a 140 main jet as I'll be using the gauze air filter rather than the paper one that used. Does sound the appropriate adjustment for the air filter ?
( anyone ever seen half depth 5/16 CEI/BSC nyloc nuts ? as the ones I sourced for the carb studs are 11mm deep which is just too deep to squeeze into the gap with a spring washer between tickler & carb flange.........I guess I have to try filing them down)
As said before, the small differences in settings discussed previously won't affect the basic running of the engine - at worse it will be down on power and may not pick up smoothly from idling. However, if the throttle slide and bore are badly worn then the engine may run very badly. In this case, tinkering with needles and jets probably won't make any difference. So it's best to start with the condition of the slide and bore. If the slide is a very loose fit then it can be replaced but, if the bore is worn, a new carb is probably required.
The slide and bore seem pretty good.
I take it from what Julian says that if I want to use the new needle & needle jet I have, then I can't use the old shorter jet holder.
So I'll have to purchase the new jet holder.
That correct
Attached is a service sheet which explains.
( complete matching set of jet, jet holder & needle jet fitted)
Does the throttle spring push directly down onto the butterfly clip?
( previously it was pushing onto metal cover that went over the old round clip(which is broken).....but looking at it and where the cable has to snag, I don't think I can use the plate it with a butterfly clip)
Just searched Amal website for the code on my carb (627/428)
and it comes up with one bike model.....a 1974 Bultaco Sherpa 350...... which on checking is a 2 stroke !! oh dear !!
Amal site says these were originally made under licence in Spain. Spec there doesn't mention the spray tube. So seems a little odd to have Norton spray tube.
Amal site says 2 stroke & 4 stroke carbs are inompatible.
anyone know what else (apart from the spray tube) differ .... that isn't cheageable ?
They differ in the spray tube and pilot jet configuration. I'm sure it will run with a 2-stroke carb but not as well as with a 4-stroke carb.
2 stroke concenric have a pilot jet which screws in (but not the bushed one), so did some early 4 stroke versions.
Later 4 stroke versions had a bushed non removable pilot jet and did not use a screw in one (new premier concentric now has a revised pilot setup).
Beig the Spanish made item will also explain the lack of O ring, had one like it some years back.
You can find it in the Amal link posted earlier.
To get the best from your bike I think you need to change that carb.
Thanks both.
I was keeping my my fingers crossed it'll do to get it on the road. So that panic over.
Anyone got an answer to my previous post. Does the throttle spring push down directly onto the butterfly needle clip ?
(can't see any other parts on the Amal guidance, but my previous round needle clip had a cover plate which doesn't look like it'll work with the new shaped clip)