From: Colin Sharpe
Date: Thu, 11 Jun 1998 12:19:47 -0500
Gregg Kricorissian wrote:
> At 12:14 AM 6/11/98 -0400, MikeT wrote:
> >Why doesn't someone make sleeved slides with stock outside diameter?
> >Then you could just buy them and plop them into a new carb to get
long
> >life without having to bore the carb.
>
> Mike,
> Very simple answer to this: the carb body wears just as much as the
slide,
> if not more, especially around the venturi. A sleeved slide would
do
> nothing to resolve that problem: you need to bore the carb body as
well,
> and fit an oversize slide.
>
> .. Gregg
A couple of points here. The first is that if what you say is true, all the stuff from people who say that a re-sleeved carb will last longer than a new one is somewhat bogus.
The second is that since the slide and the body are both made of zinc alloy, the wear characteristics may well be worsened. Note that any plain bearing/bushing uses dissimilar materials, such as steel and bronze, to maximise life. The carburettor is a particularly bad item from a wear point of view, since it gets no lubrication (Except on a 2-stroke). If the air cleaner is not up to snuff, it could also be abraded by road dirt.
-so-
We need more information before we can make a recommendation on this, but a slide made from something other than mazac or "Welsh Silver"(See Monty Python's Big Red Book for details), might help. Perhaps in these days of CNC machining, a prototype or two might be a possibility without tooling up for die casting.
English.
Date: Fri, 12 Jun 1998 04:58:41 -0700
From: Gary Slabaugh
Adrian Morgan wrote:
> Please, who are AMR?
> > > Doesn't AMR still do a Mikuni slide (chrome plated brass) conversion
for
> > > Concentrics?
There has been several inquiries about AMR's Mikuni slide conversion for Amal Concentrics. They can be found at:
http://www.rtd.com/~amr/
I have two of the original prototypes in my 750 Combat installed back
in 87 and 30K miles ago. The slides and inside of the carbs still look
like new. Only one slight problem I have encountered and that is sometimes
wishing for a choke during our cool winter months when we are forced to
use special brew lean burn fuel with a high alcohol content. It is also
important to replace the needle and needle jet after the mod or the carb
will run too rich after warm-up because of new tight tolerances of slide
to carb fit. I also have a pair of the modified carbs on my 850 Interstate
that I had to pay for.
--
Gary Slabaugh Tucson, Arizona
2.2 Concentric Production Tolerances
Date: Thu, 11 Jun 1998 10:26:23 -0400
From: Gregg Kricorissian
Dear all,
This is a long posting, so feel free to skip ahead...
With all the recent talk about the relative superiority of Amal and Mikuni carbs, I began to think more about the effect of production tolerances on the Concentric carb.
The differences in the styles of needle jets, needles and jet holders have been well documented, as have the sloppy tolerances of the orifices in aftermarket jets. However, I have not seen anything about the effects of dimensional variations in the jet holder.
One end of the jet holder suspends the main jet in the float chamber while locating the needle jet with respect to the needle at its other end. Since the relative position of the needle and needle jet have a primary influence over the mixture for most of the riding we do, this relationship is very important. I decided to examine a few jet holders last night, in a moment of introspection.
I measured the overall length of the jet holder, which I found to be quite uniform over the 10 samples I checked. However, the critical measurement is the length of the "threaded portion" of the holder, since that is the dimension that determines the relationship of the needle and the needle jet. Unfortunately, I found a lot of variation on this dimension: about 0.015" over the samples I evaluated. Interestingly, they paired up nicely in two's, within 0.001", so I'll bet that Amal controlled machining tolerances within batches, but certainly not among batches!
This means Lord help you if you simply took any two jet holders from your collection, and used them to build a pair of carbs. You would end up with one carb running too lean or too rich.
A related thought is that the machining for the jet holder in the carb body is quite critical: not only the absolute measurement, but also relative to the dimension to which the jet holder was finished.
Similarly, the later needle jets are counterbored, so that metering is done "down inside" the jet body. The depth of this counterbore is critical to metering as well, and subject to production tolerances.
This may be a point in which the Mikuni may be superior, since the position of the needle jet is set directly by the machining of the carb body, rather than by an interposed jet holder ... fewer dimensional tolerances to worry about. However, you'll still find Amals on all my Brit bikes.
It's always been good practice not to mix and match parts in precision assemblies, and this is just another case to prove the point. However, since most of our bikes are over 20 years old, it's anyone's guess what the DPO's may have done. Best to check your carbs carefully when you have them apart, and don't take anything for granted!
Food for thought?
.. Gregg
Date: Wed, 29 Jul 1998 10:23:49 -0700
From: Mel Ray
Much has been speculated recently about other-than-amal carbs on B-I, I can add some supporting real-world fact to the discussion. Short story is, if you are not of the "it has to be stock" school, CV carbs are as huge a leap forward as pointless ignitions.
Way back once upon a time (about 1974) with some help and encouragement from a fellow now known as the Phantom Oiler, I swapped a pair of rattling, clanking worn out amals for a set of 38mm CV mikunis from an early 650 Yamaha twin onto a medium hotrod 650 Triumph which I still have (you can see em peeking out in the photos on Phantom Oiler).
This was very unscientific, the carbs came from someones' trash (I think Bin is the proper Brit term) which was exactly the price I could afford, We took the trouble to make up adapters that utilized the stock Yamaha soft mounts, which then took some sorting as the vibration on this one was once about an 8 on the Richter scale, tore the rubbers.
The experiment was a huge success as to easy starting, idling even on JOMO 15 spec cams, snappy throttle response, very light cable pull, and fuel economy jumped to over 60 on the highway when ridden easy. Oddly, the carbs are not too big even for the 650cc the engine currently displaces. Igniton failure at upper revs was not solved.
If you run a cv with the filter off you can slip a probe (don't drop it) or your finger in the mouth while running, check how far the unit is actually opening under different conditions. I'm amazed to find that this old Triumph is happy using the whole 38mm, from about 35-3800 RPM.
Big carbs will definitely illustrate any weakness in the ignition system, this particular engine never really ran right on top end (well DUHH, it was ET) until I fit a boyer. Now it pulls the tallest gearing I can put on it, full revs in top gear (127-128 mph by my GPS).
A 650 with less cam and head work might not like such big ones, dunno- oh almost forgot, SMALL exhaust pipes are essential to making them work. I have an 1 3/8" 2 into one Triumph T-bird pipe from 1963 and one early straight-thru muffler (it is surely NOT a silencer), the pipe is not as well done at the joint as some Armour pipes I've seen recently, but it works and looks right. TT pipes look great but don't work, except to make most noise per cubic...
If junk-yard shopping for similar carbs, be sure to get the rubbers off the engine too- these parts are scarce if there are any dirt track racers around as the Yamaha big twins shake pretty bad too.
I also just adapted a set of 34mm CVs from a Yamaha 850 triple to one
of my T150s, but that's a story for another day.
--
Mel Ray Nottage
NetGroupInc
Date: Thu, 30 Jul 1998 10:48:14 -0400
From: Frank Palmeri
I have an old Chilton general motorcycle repair manual. I've always loved the part where they try to explain how CV carbs work. It's something like "CV carbs are just like throttle slide controled carbs, except the throttle controls a valve in the intake air stream instead of the slide directly..."
Excuse me! This sounds to me like CV carbs are VERY DIFFERENT from throttle slide controled carbs!
Anyway, I've always wondered about the whole "constant velocity" and "constant vacuum" theory behind these carbs. In essence when you twist the valve open between the carb and intake vaccuum, the vacuum sucks air from the top of the carb, which pulls the slide up, which lets more air in. I know it works, and works very well, but you have to admit it's so fundamentally different from the cable just pulling the slide up that it's confusing.
Too bad I don't have the time or skill to go to a wrecking yard and pull a pair of CV's off a UJM an get them fettled. If someone put out a kit with the proper jetting, cables, etc., I'd certainly be interesed.
It's funny. Commando's haven't been made for over 20 years. Yet every
now and then someone will come out with some marvelous upgrade, like the
automatic camchain tensioner. Apparantly there's still somewhat of a market
for these bikes. I'd love to know how many Commando's are actually running
today, using tires and oil and filters, etc. Is the number increasing,
decreasing, or staying the same?
___________________________________________________________________________
Frank Palmeri
1975 Norton 850 Commando Interstate ridden daily/cleaned less
1987 Honda Z50R my son's dream bike, but I like it too
1967 Montgomery Ward's/Benelli Riverside 350 sitting in boxes awaiting
my
attention
___________________________________________________________________________
2.4 Mk1 Concentric Float Bowl Types and Sizes.
Date: Fri, 12 Jun 1998 16:39:15 +0100 (BST)
From: Philip Pick
On Fri 12 Jun, Peter Aslan wrote:
> I have still never received an answer to a question on Amals posted
here
> twice in the last 2 years.
> The Amal parts list, lists several different types of float bowls,
not
> just two , one for two stroke and one for four, but about 5 or 6
separate
> types.
>
> The question is, why the range of types. It can only be for different
> float heights or different sizes of needle seats, to allow more or
less
> petrol to enter the carb for different types of fuel or different
> applications.
Oh ye petulant one. If somebody had thought the question was worth an answer........
but to be dry and uninteresting I have some old Amal info. That gives the following:
For Petrol
622/050 Float Bowl - 0.10 seatingMost normal bikes will have .10 Seating for the float needle. Pumped systems need a smaller hole so will use .062 seating float bowls. I guess an installation with a very low feed pressure or high demand may need the .125 seat
622/055 Float Bowl - 0.10 seating, with drain plug
622/052 Float Bowl - 0.062 seating
622/057 Float Bowl - 0.062 seating, with drain plug
622/051 Float Bowl - 0.125 seating
622/056 Float Bowl - 0.125 seating, with drain plug
For Alcohol
622/050 Float Bowl - 0.156 seating, use with 622/149 float needle.Happy Now?
regards
--
Philip Pick
Date: Wed, 17 Jun 1998 20:02:54 -0400
From: Gregg Kricorissian
Hello Peter,
Thank you for the kind words about my posting on Amal tolerances. I took my own words to heart, and my Concentrics are running very well indeed.
Sorry I hadn't noticed you had directed your question at me. Regarding your question about why Amal listed so many different bowls, I'd have to agree that some may be, as you say, to accommodate different fuel levels, and flow rates.
Of course, then there is the variant with the removable plug for accessing the main jet, though I haven't seen much of any information relating to any of it.
.. Gregg
2.5 Mk 1 Concentric Float Height Adjustment
Date: Fri, 26 Jun 1998 14:42:17 -0500
From: Barb McFarland
If you haven't already gotten an answer here is what I did:
The INOA Tech Digest says that the floats in Amal carbs should sit 3/32 of an inch above the edge of the float bowl with the float seated into the bowl. You have to heat the float up and use a punch to raise and lower the float valve seat.
I just adjusted mine and set them to that. Now all is well and are running great!
Good luck!
Bob McFarland
2.6 Mk1 Mk 1 Concentric Idle Jet.
Date: Wed, 8 Jul 1998 09:11:21 -0700
From: Tony Mackay
I got a new Amal 930 Concentric recently and noticed that the 25 ccs slow running jet was missing from the underside of the body (although the female thread to locate it had been tapped). In exploded views, some of the manuals show this jet and others don't and there is a note in one of the books which seems to suggest that the Needle/Main Jets are differently sized to compensate for not having a slow running jet (and just letting the engine suck up as much fuel as it needs through the slow running drill holes).
I would appreciate knowing if all is in order here.
Many thanks........Tony Mackay.
Date: Wed, 8 Jul 1998 10:31:27 -0700
From: John Mead
Almost all new Amal Concentrics are drilled for the pilot jet. I think it is for the 30cc one. On my Vincents 30 is too rich and I just screw 25cc jets into the body. This allows me to get the correct adjustment on the idle mixture.
John Mead
Date: Thu, 9 Jul 1998 09:51:28 +0100
From: Philip Pick
On Wed 08 Jul, Mr. A. Mackay wrote:
> I got a new Amal 930 Concentric recently and noticed that the 25
ccs
> slow running jet was missing from the underside of the body
{Snip]
I presume the carb was ordered as a 4-stroke type.
The pilot jet is fitted, as a brass (non-removable) piece pressed into a drilling. If you take out the pilot air screw and look deep into the body, at the far end of that drilling you will see the ring of brass, with a .017inch hole. That's the jet.
It is sized as a 25.
Needle Jets, Main Jets, Jet Holder and spray tubes are different for 2 or 4 stroke use.
I believe for 2-stroke use the fixed pilot jet is not fitted and the removable one is used, screwed in to old position in the body.
The fixed jet was not fitted until 1969, so '68 bikes that had Amal Concentric in the first year of major carb production had the pilot jet in the screwed in position.
Regards
--
Philip Pick
2.7 Mk 1 Concentric Idling Problems.
Date: Mon, 08 Jun 1998 20:03:31 -0500
From: Rick Tyson
Thanks to all who provided advice for sorting out my head torque/bolt(stud) inquiry. It is of course rather straightforward if you just think about the bolt(stud) size rather than the head(nut) size. I so enjoyed the experience that I torqued the head a total of five times. Just a little added insurance.
Looks like I'll get the opportunity to check out at least one of the suggested causes of my unpleasant noise that occurs when the throttle is "blipped". Since there appears to be a rather noticeable oil leak from the region of the primary cover, I imagine that removal and seal/gasket replacement will be my next order of business. I'll take a careful look at the alternator and anything else that might be responsible for the noise.
Unfortunately, other problems continue to plague the '75 MkIII. The most frustrating is trying to get the silly thing to do what it is supposed to at idle and slightly beyond. There appeared to be some type of "minor" carb problem before I began the restoration this past winter. The right (timing side!) carb would only work when the idle mixture screw was a quarter turn out. Any further out and the flame would die. So before I put it back together I thoroughly cleaned everything and installed new needles, needle jets, and main jets. When first together the bike ran pretty well, both mixture screws were approx. one and a half turns out. During the past couple of weeks, things have gotten progressively worse. Now when I start the bike cold it appears to run on one cylinder and backfires through the exhaust like crazy. If I keep it running, it can be ridden and when warm, it actually seems to idle and run OK. If I adjust the idle and mixture screws on the warm engine, the bike seems to run OK, but when cold the same old story again. I've read the many reports on worn Amals. As far as I know the carbs on my Commando are the stock originals. The bike appears to have approx. 30,000 miles. on it. Are the symptoms that I have described caused by worn carb slides. Since I have no experience in these matters, I have no clue where to go. I've even tried a mercury vacuum gauge for balancing the carbs but everytime I turn a screw, I seem to see the opposite of what I expect to happen. Are there problems other than fuel systems problems that can cause these symptoms?
Any wise and knowledgeable advice from the loyal readers? At this rate I'm going to end up spending a lot more riding time this summer of the Trident than I had planned and leave the Commando under a tarp in the garage!
Rick Tyson
Date: Tue, 9 Jun 1998 02:25:43 -0400 (EDT)
From: Steven R. Schoner
Reply to message from dryheat of Mon, 08 Jun
>Being that 90% of carb problems are electrical, I solved my starting
and
>idling "features" associated with my old amals by purchasing a serious
>flame throwing Andrews high output dual lead coil and properly disposing
of
>the two Lucas coils. I bought it from Stan at Rocky Point Cycle, I
think
>about $75 or so.
>
>When we are born, we cry, that we have come to this stage of fools.
> Blinded by the Light at NUTS.com Lear 4.6
As everyone knows my love for Mikunis, I too, canned the Lucas coils and opted for a Harley yellow coil. Fits real nice under the tank, and no resistor is required. It works perfectly with the Boyer ignition.
No problemo
--
Steven R. Schoner (Meteorite Man and Seeker)
___________________________________________________________________________
Compared to the Infinite we know next to nothing. What good we do with
the little we do know is the key to wisdom.
Date: Tue, 9 Jun 1998 07:21:19 -0700 (PDT)
From: Thomas H. Allen
Rick Tyson Wrote:
>The bike appears to have approx.
>30,000 mi. on it. Are the symptoms that I have described caused by
worn
>carb slides. Since I have no experience in these matters, I have no
>clue where to go. I've even tried a mercury vacuum gauge for balancing
>the carbs but everytime I turn a screw, I seem to see the opposite
of
>what I expect to happen. Are there problems other than fuel systems
>problems that can cause these symptoms?
[SNIP]
The answer to the carb problem is long in the telling but I'll take a quick stab at it ant then look for a collection of posts from Brit iron a couple of years ago on the subject.
First, it sounds like your immediate problem is that the pilot circuit(s) are plugged or partially so. If you're lucky you can cure this with a few doses of Red Line S1 fuel injector cleaner added to your gas. If that doesn't work unscrew the idle mix screws and poke into the hole with a paper-clip sharpened to very fine point (it has to fit through a hole that passes 25 cc of fuel per minute. Get a #25 pilot jet and look into it to see how small the hole is. If that doesn't work you'll have to wait for the post on drilling out the blanking plugs to get access from behind.
If the slides are indeed loose you will go nuts trying to achieve a stable tune particularly at idle. The solution is to sleeve the slides and rebore the carbs, about which much has been said already and no doubt will be again soon. I would not invest in sleeving the carbs until you get the pilot circuit blockage sorted out. Since you believe you have both problems, you might consider buying two new carbs. You'll get around 17-20 thousand miles before you have to sleeve them.
Date: Tue, 9 Jun 1998 07:26:34 -0700
From: Ben & Linda
Rick Tyson Wrote:
> Unfortunately, other problems continue to plague the '75 MkIII. The
> most frustrating is trying to get the silly thing to do what it is
> supposed to at idle and slightly beyond.
[Snip]
Perhaps, but clogged idle drillings are equally likely to be the culprit. You need to dissemble the carbs completely and soak the bodies in the eat-your-skin-off type carb cleaner (@ $30 for a can big enough for one carb at a time at auto parts stores).
When you take them out of the bath, use compressed air (or a spray can solvent like brake cleaner) to blow through the idle passages. They are small drillings that connect a hole in the front air inlet, a hole that connects into the float bowl, the mixture adjusting screw hole, and a spray hole right downstream from the slide (next to the manifold). I hold fingers over two holes and spray into one other to see that the last hole is clearly open to all others. Rotate around until all are seen to be clear. If not- back into the soup.
Extreme cases call for drilling out the plugs Amal put in to plug up the original work drillings. Sort of reproducing the factory manufacturing process.
Many of the slide sleevers offer this service as part of their package. With today's high detergent (for car fuel injection) gasoline, you'll never have to do it again.
Ben English
1972 Norton Commando Combat Roadster #201695
1982 Honda FT500 Ascot / 1972 Olmo 10 speed
Amtrak National Timetable / Pocket full of bus tokens / Good shoes
USNOA 1395 / NOC 06Z06.2530 0 / MGNOC 15713
Scowling Street Terrors 2 / Skinny Tire Motorcycle Club 3
Lower East Side Egyptian Cobras 4 / Hells' Vegetarians 5
Denizens of Doom 304
Date: Tue, 9 Jun 1998 12:15:32 -0400 (EDT)
From: Steven R. Schoner
Reply to message from bucbean of Tue, 09 Jun
>At 02:25 AM 6/9/98 -0400, you wrote:
>>Reply to message from dryheat of Mon, 08 Jun
>>>Being that 90% of carb problems are electrical, I solved my starting
and
>>>idling "features" associated with my old amals by purchasing a serious
>>>flame throwing Andrews high output dual lead coil and properly disposing
of
>>>the two lucas coils. I bought it from Stan at Rocky Point Cycle,
I think
>>>about $75 or so.
>>
>>As everyone knows my love for Mikunis, I too, canned the Lucas coils
>>and opted for a Harley yellow coil. Fits real nice under the tank,
and
>>no resistor is required. It works perfectly with the Boyer ignition.
>>
>>No problemo
>
>Would this be a 12v. Coil? Where did you mount it?
>
>Thanks.
>bucbean
>70 Commando with High Rider tank.
Yes, it is the standard 12v Harley Coil. Yellow, and make of some kind of thermoplastic. The mounting holes are on the top of it on a flange that is in line with the poles of it. The high tension wires come out perpendicular to that flange, and perpendicular to the coil body.
Now, there is holes already on this top mounting flange. Beneath the Norton gas tank and on the front end of the frame just behind the steering yoke is the mounting arms for the tank. The old dual coils also fit to this,a nd the holes are already there. What you need to do is make up a bracket that fits to the two holes in these arms and is also drilled so that you can attach the Harley coil with thru bolts.
No big deal. A small lenght of 1/2" angle alum. will do the trick. Drill the holes for the coil, and then for the tank mounting arms, but you don't have to drill the arms, as the holes should already be there.
Use a strip of tube rubber to help insulate the coil from vibration, hook it up andy you are set to go. Looks like it was made for it.
--
Steven R. Schoner (Meteorite Man and Seeker)
___________________________________________________________________________
Compared to the Infinite we know next to nothing. What good we do with
the little we do know is the key to wisdom.
-
2.8 Mk 1 Concentric Renovation.
Date: Tue, 03 Feb 1998 16:46:58 +1100
From: Chris
Glen wrote;
> My question is: how much is too much play between the slide and the
body.
> An expierienced Nortonian I'm sure could just rock the slide and
decide
> go-no go.
While someone may write in with a "so many thou" answer I doubt it. The test seems to be whether the bike will give a tuneable and consistent idle. (yes I mean relatively consistent.) The mileage is consistent with worn.
> Also my friendly local British parts supplier told me when I purchased
the
> Amal kits that the needle jets and needles also are prone to wear
and
> should be replaced. He says this causes rich mixture and leads to
fouling
> plugs. This guy is truly a British bike expert, and I don't doubt
him, I'm
> just wondering if this is common knowledge and if everyone does it
as a
> matter of course.
Yes, it is common knowledge. Everyone I talked to when trying to get my Commando sorted said somewhere up the front of the conversation, "what are the jets like". Just as with the slides I resisted this insight. When I finally cracked and replaced the needles and jets the bike was smoother, more powerful, more consistent in the tune plus I reckon the gas saved paid for the parts in a short time. The reason they wear is the needle is not rigid and with the vibration must constantly be hitting the sides of the jet.
Hope this helps
Chris Ghent
From: Jordan Princic
Date: Tue, 30 Jun 1998 19:28:25 +1000
Colin Sharpe wrote:
> since the needles bouncing around in the jets will wear them, allowing
> more fuel to pass. I'd do it if I had problems which seemed to indicate
> a rich mixture, such as having to use Bosch Platinum plugs to avoid
> fouling. (I'll duck here!).
>
> English.
Does anyone have any objections to lowering the needle (raising the clip)as a remedy for jet wear? It would seem a logical no-cost solution. Jordan
Date: Wed, 01 Jul 1998 07:41:25 -0500
From: Mike Selvey
Charles R. Lipton wrote:
> Jordan wrote,
>> Agreed, it would be hard to guarantee that the original settings
are kept,
>> but lowering the needle in a worn jet might approximate the correct
effective
>> hole size, surely? That is to say, it might be better than leaving
it as it
>>is. Or am I barking up the wrong tree?
>
> In short, I don't think it's a good idea for a long term solution
> ... like not further than the next paycheck or until the mail horse
> next arrives. I am going to keep my rear end in this chair and not
> get up to get any resource material. If I miss something in this
> thought experiment, the rest of you please be gentle with your
> criticism.
>
> In real life, there are actually two things happening when a jet
> wears: First, the hole in the needle jet is worn out of round,
> usually extended fore and aft as a result of erosion from the steel
> needle striking the edges of the brass jet as the engine rocks during
> running) and, in many cases, the needle itself gets a groove or two
> worn in it (especially at constant throttle openings -- where the
> needle is often in contact with the sides of the jet -- as well as
> larger throttle openings where the needle's metal is thinnest for
> those who like to turn up the wick often).
>
> This means that the amount of the jet's hole being uncovered by the
> raising of the needle increases at a fairly constant rate when both
> parts are new, but when the needle gets worn at certain places, you
> get sudden rich spots. If you lower the needle in the jet, you are
> reducing the amount of fuel flow (leaning the mixture) at low speed
> settings and you are moving the rich spots up the throttle opening
> range (the latter isn't necessarily a negative but I can't think
of
> anything good to say about it either). As a get home trick, this
> might be all right, but I wouldn't want to do this very long. There
> may be a way to compensate for the leanness at low throttle, but
I
> can't see where this could be a long term benefit.
>
> Opposing opinions and corrections are welcomed.
>
> Charlie Lipton
Charlie and Jordan-
I agree with Charles here. He puts it far more eloquently than I used to when I worked a parts counter at a British bike shop. My simple explanation was that the needle in time wore the jet diameter into an "ovoid" shape, therefore NO amount of fiddling with the needle height setting would compensate for the fuel rushing past. It would ALWAYS run slightly rich, after the needle-to-surface area was worn.
Replace the needles and needle jets. It's really that simple....and not that expensive.
Just my opinion.
Mike Selvey
'72 Norton Commando Interstate
Nacogdoches, TX
Date: Thu, 23 Jul 1998 11:26:48 +0100
From: Aslan, Peter
The following has been kicking around my hard drive since I copied it out some years ago. Following discussions of setting up Amals, I thought I would finally post it.
Judging from the references to 'Sparkling Plugs' and 'Adjusting the Ignition for Best Slow Running' I would assume the original text is circa 1950 or before, but it was definately produced, (or Revised) for the Amal Concentric, which goes to show how old these bits now are.
FWIW, I also think the Concentric is a good bit of Kit, Cheap but efficient.
Regards, Captain Norton.
Notes:
1.0 MAIN JET.
With Throttle in position 1, (Fully Open).
If at Full Throttle the engine runs "Heavily" the Main Jet is too large. If at Full Throttle, by slightly closing the Throttle or Air Valve, (Choke) the engine appears to have better power, the Main Jet is too small.
With the correct sized main Jet the engine at Full Throttle should run evenly and regularly with maximum power.
If testing for speed work ensure that the Main Jet is sufficient for the mixture to be rich enough to keep the engine cool, and to verify this examine the sparking plug after taking a fast, (Full Throttle) run, declutching and stopping the engine quickly. If the plug body at its end has a cool appearance, (light Tan on the Spark plug insulator up next to the centre electrode) the mixture is correct: if sooty, the mixture is rich: if however there are signs of intense heat, (white with particles on the insulator) the mixture is too weak and a larger main Jet is necessary.
2.0 PILOT JET.
With the Throttle in position 1, (Closed).
With the Engine running too fast with the twist grip shut off and the Throttle shut down on the Throttle adjusting screw, and Ignition set for best slowrunning: (1) screw out the Throttle adjusting screw until the engine runs slower and begins to falter, then screw Pilot air adjusting screw in or out to make engine run regularly and faster. (2) Now gently lower the throttle adjusting screw until the engine runs slower and just begins to falter, adjust the Pilot air adjusting screw to get best slow running: if this 2nd adjustment makes the engine run too fast, go over the job again a third time. Both the throttle adjusting screw and Pilot air screw have an 'O' Ring fitted to hold the adjustment by friction.
3.0 THROTTLE CUT AWAY.
With throttle in position 3, (1/3rd Open).
If, as you take off from the idling position, there is an objectionable spitting from the carburetor, slightly richen the pilot mixture by screwing in the air screw sufficiently, but if this is not effective, screw it back in again, and fit a throttle slide with a smaller cut away. If the engine jerks under load at this throttle position and there is no spitting. Either the jet needle is much too high or a larger throttle cut away is required to cure richness.
4.0 NEEDLE.
With the throttle in position 4, (3/4 Open).
The needle controls a wide range of throttle opening and also the acceleration. Try the needle in the lower position, with the clip in the groove at the top; if acceleration is poor and with the air valve, (Choke) partially closed the results are better, raise the needle by two groves; if very much better try lowering the needle by one grove and leave it where it is best. If the mixture is still too rich with the clip in grove No 1 (nearest the top) the needle probably wants replacement because of ware. If the needle itself has had several years use replace it also.
5.0 FINALLY.
Go over Idling again for the final touches.