Choke removal

I hate to say it in this herd of Amal lovers but the old concentric is a pretty crude instrument.
The fact is that they will run with the choke removed and they just aren't lean like the final bikes that used more sophisticated carbs.
You can also use the arguement that there is a bit less to go wrong with no choke on an Amal.
Why did they get rid of the tickler? Dumping raw gas out like that is polluting.
Most modern bikes are barely going to run without a choke, if at all.
All in all the Amal is gone except on antiques and fuel injection is cleaner and better.
But since this discussion is about antiques, take your choice! It's your bike and they will run either way.

I agree,

If the rather rudimentary Amal Mk1 carb is compared to other more sophisticated carbs such as Mikunis or Keihins for instance, with their vast range of needles, needle jets, air jets, pilot jets, etc. then the Mk1 Amal has to be regarded as something of a blunt instrument that can only be tuned in very course stages using the limited choice of needle jets, ONE standard 4-stroke needle that has only three grooves, no pilot jet adjustment as standard (except on the earliest and latest Mk1s and 2-stroke Mk1 versions).
Although it's relative simplicity and ease of tuning is also its strongest point, but I do seriously doubt that a Mk1 Amal can be set up anywhere near as accurately as an experienced person could do with a Mikuni, so I think the majority of us Amal users have to settle for somewhat less than optimum mixture settings most of the time?

Cookie said:

I hate to say it in this herd of Amal lovers but the old concentric is a pretty crude instrument.
The fact is that they will run with the choke removed and they just aren't lean like the final bikes that used more sophisticated carbs.
You can also use the arguement that there is a bit less to go wrong with no choke on an Amal.
Why did they get rid of the tickler? Dumping raw gas out like that is polluting.
Most modern bikes are barely going to run without a choke, if at all.
All in all the Amal is gone except on antiques and fuel injection is cleaner and better.
But since this discussion is about antiques, take your choice! It's your bike and they will run either way.

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Thanks Cookie, you summarized what I'd been thinking. It's 41 years since the Commando engine evolved from it's predecessors. In modern engines every bit of metal in every part has been carefully planned out in the greater scheme of things.

The other silicon injection to the amal is the throttle stop screw. Why have it? The cable does the same adjustment. If the throttle stop screw pushes your slides past where your cable bottoms out then when you 1st turn on the throttle nothing happens till you catch up to where the throttle stop has raised the slides to. Why? If your throttle cable is set right and has a clear path from the grip to the carb you don't need a throttle stop screw and there is no slack in your throttle cable

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"

I doubt many (if any) Commando owners would use "maximum power" or anywhere near it, with a cold engine if they have any regard at all for the well-being of their engine's internals!"

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You completely missed my point. What I am saying is that, if the motor was able to start cold without choke, once warm the bike will run rich and you will have a performance drop off compared to a warm engine and properly jetted carburetion.

montelatici said:

You completely missed my point. What I am saying is that, if the motor was able to start cold without choke, once warm the bike will run rich and you will have a performance drop off compared to a warm engine and properly jetted carburetion.

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On the contrary, I fully understood what you meant.

But just because an engine may be rich at the throttle settings used during warm up, it doesn't necessarily follow that it will be rich at all throttle settings.

Correct, if your main jet/needle is correct at 3/4-full throttle (full main jet) it might not be rich at those settings when warm. But at the throttle openings that you are running it while it is cold (if it runs at those openings without choke), it will be rich when warm, if it ran at those throttle openings when cold.

montelatici said:

But at the throttle openings that you are running it while it is cold (if it runs at those openings without choke), it will be rich when warm, if it ran at those throttle openings when cold.

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Certainly, and I wouldn't disagree, but when it comes down to adjusting a pair of (generally) worn Amals, then the whole process of trying to get the mixture absolutely correct at small throttle openings becomes a bit of a waste of time. I cannot speak for others but as far as I am concerned, I am content if my Commando runs reasonably well without exhibiting signs of excessive richness or weakness whether it needs choke for cold running or not. :wink:

If you are happy, that's all that matters. But even in India tuners know that if a bike starts unchoked when cold, it will be running rich when it warms up.

http://www.nandanmotors.com/start2.html


"What it does is open a valve letting a lot more fuel get drawn into the engine. NOW we are in a position to analyse the myths about chokes ! If the engine can start cold without the choke, it means it is getting enough fuel for that thru the slow-speed jet. So it's quite likely the jet is bigger than necessary, wasting fuel when the engine is hot ! Or, it may be that the "air-screw" is adjusted too rich, with similar effect. Or, the fuel level in the float chamber is set too high. Or, the engine has been flooded already and hence starts. In short, it is "two negatives making a positive". Nothing to be happy about!"

The original question was whether it was possible to run a Norton without the choke mechanism installed, the short answer is yes and blanking plugs are available to accommodate this, however there is a caveat depending on the environment in which it is to be used. Enough of us have run without a choke and are convinced that this has no adverse effect on the optimum mixture for normal operating temperature that there seems to be something in this.

I normally start mine on ticklers and then keep it running by holding/blipping the throttle until it settles down (quite quickly unless it's unusually cold), I then check the oil level and only then ride the bike. It doesn't usually run particularly well until I am a few hundred yards up the road and on those odd occasions where I have simply bump started it from cold down the hill and ridden away, it is pretty rough until it warms up, because it is indeed running too lean under these conditions. It would undoubtedly run smoother with the choke on but the added complexity and possibility of broken cables has lead me to dispense with this. I like to warm my bike up without any load to get things flowing, so there is no inconvenience attached to this at all. I have spent a lot of time jetting the bike to what I consider optimum settings and I am convinced that it is not running too rich. One benefit I can see of running a choke system is if your throttle cable breaks out on a run you could cobble it back together using the choke cables to get you home.

I am not surprised that "even in India" they understand carburetor theory, the Enfield factory is a modern and high tech manufacturing facility and their lean-burn carburettors are designed to meet stringent worldwide emissions regulations.

Technical and theoretical discussions are fun and montelatici has contributed some interesting and one has to admit theoretically accurate points to the debate, perhaps paradoxically, as with my bumble bee analogy, the physics here is so much more complex in an old inaccurate system than it would be under laboratory conditions. However running these old bikes seems to require equal parts of Physics, Alchemy and bloody-mindedness and this is where the literally thousands of man-years of experience that we have available here makes this forum such a unique resource for seeking advise.

And now I know that to stir you guys up all one needs to do is mentions chokes or oil.

montelatici said:

If you are happy, that's all that matters. But even in India tuners know that if a bike starts unchoked when cold, it will be running rich when it warms up.

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Everyone agrees that a bike that starts with out a choke or tickler is probably rich. But you have to agree that starting with tickling can be used on a properly tuned bike and it will start. Or are you just trolling us now?

"But you have to agree that starting with tickling can be used on a properly tuned bike and it will start. Or are you just trolling us now?"

I never said that starting with tickling is not possible. I have said that if it starts (with tickling) without choke, the bike will be running rich once it warms up and hence the bike is not properly tuned but running rich. It is just physics, can't get around it.

And as far as the "trolling" accusation, why don't you grow up. This has been a civil discussion until now.

montelatici said:

"But you have to agree that starting with tickling can be used on a properly tuned bike and it will start. Or are you just trolling us now?"

I never said that starting with tickling is not possible. I have said that if it starts (with tickling) without choke, the bike will be running rich once it warms up and hence the bike is not properly tuned but running rich. It is just physics, can't get around it.

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You can have a properly tuned bike that starts with tickling. You haven't shown otherwise.

What we have here, is a failure to communicate. (It's from a movie). There is a difference between what it takes to get a motor started and what it needs to keep it running while it warms up. Ticklers will get it started but it's the pilot circuit it'll be running on during warm up. There was a guy on BritIron years ago that was a petro-engineer. He made the point that it is a fact that if the engine runs great, or even at all, cold without choke, then it's set rich. He finally won people over. Did they go out and re-tune their Amals? No. It didn't matter that much then and it doesn't now. It sure would be helpful if listers would uses their first names. It feels awkward referring to people by their none de net. And giving up some of that anonimity might make people just a little more real.

bpatton said:

What we have here, is a failure to communicate. (It's from a movie). There is a difference between what it takes to get a motor started and what it needs to keep it running while it warms up. Ticklers will get it started but it's the pilot circuit it'll be running on during warm up. There was a guy on BritIron years ago that was a petro-engineer. He made the point that it is a fact that if the engine runs great, or even at all, cold without choke, then it's set rich. He finally won people over.

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I won't even argue that. Not sure why it was even for discussion. If your bike starts (without choke or tickler) from cold it's too rich. Especially if it idles from cold.

Did they go out and re-tune their Amals? No. It didn't matter that much then and it doesn't now.

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I'm sure someone who had their carbs set way too rich may have.

It sure would be helpful if listers would uses their first names. It feels awkward referring to people by their none de net. And giving up some of that anonimity might make people just a little more real.

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Some forum owners require that. About all it helps is that you have a real name to go with the attitude. :mrgreen:

Interesting thread here. As a datapoint though, I've never seen a Manx with the choke installed in it's GP carb. Mine starts just fine without the choke installed after tickling the fuel bowl a bit. Starts up and stumbles for a few seconds, but warms up fast. Both plug chops and dyno runs after warmup indicate a good open throttle mixture. If anything, it runs a bit lean on the needle.

As you well know, on a dyno your plug chop is based on the throttle opening where you achieve peak power (because you shut down after the run for that purpose), not at lower throttle openings that you are starting the Manx cold with. It could very well be that the main jet is the correct size and needle set correctly and at high throttle openings you are not running rich. In any case the guys that I race with who have Manx's, start their Manx's with foam in the stack for choke. Once they warm up they take out the foam and run on the stack.

But again, this is like arguing about what temperature water boils at. Ask any engineer, tuner, etc. and they will tell you the same thing. If your carbureted engine starts and continues to run without choke when cold, by definition it will run rich when the engine warms up.

I think that an important point here is that most of us with long experience of Nortons could make an engine start and run using a squeezy bottle full of fuel and a pad of cotton wool.

I'm still puzzled as to the function of the Concentric's choke. At initial start-up, it's function is doubled up by tickling and if the choke is backed off to half as the motor warms, it is simply doing nothing as the slide is always lower in the carb bore.

What should an assembler, as opposed to an engineer do with his Concentric carbed Commando ? My carbs have a pilot bush so nothing to normally change there. I set my pilot air screw as per the book on a warm engine so it shouldn't be too rich. I have altered needle positions and changed slides and one groove or a 1/2 cutaway leaner causes definite signs of weakness.

As L.A.B. says, the Mk 1 is a bit of a blunt instrument to tune and perhaps it is so that a smooth accelerating Commando needs a slight richness low down. Could it be that the low frequency vibration causes eratic carburation at low rpm and that this is best disguised by a slight richness, the end result being a better-mannered road bike ?

HI a bit confused by this comment you made

"To start maintain running a cold engine the mixture needs to be between 11.01:1 and 10.3:1 depending on the ambient temp.

The above mixture ratios are pretty much accepted by tuners, although to meet emissions requirements engines run much leaner than optimum these days"

are you saying that moderen engines are runing outside of the 11.01 : 1 10.3 : 1 range when running cold have been following the discussion so far and this bit lost me

montelatici said:

If a motor starts without choke and continues to run when cold, the mixture will be, by definition "rich" when the motor warms up.

For a gasoline engine stoichiometry (the chemically “correct” point at which the most complete combustion takes place under no load) is 14.7 parts air to 1 part fuel (14.7:1).

Steady state throttle under steady state load the optimum mixture would be about 13.2:1 and with this you get peak Brake Mean Effective Pressure (BMEP).

Under acceleration the correct mixture with a cold engine is 12.1:1 and when warmed up 12.7:1. (You can see why "pumper" carburetors are performance enhancers, alternatively, you adjust the mixture somewhere between the steady state optimum and the acceleration optimum on conventional carburetors)

To start maintain running a cold engine the mixture needs to be between 11.01:1 and 10.3:1 depending on the ambient temp.

The above mixture ratios are pretty much accepted by tuners, although to meet emissions requirements engines run much leaner than optimum these days.

So, while a rich mixture is certainly preferable (and the bike will run satisfactorily) to a overly lean mixture, running rich reduces performance somewhat, uses more fuel, causes more carbon build up and over time introduces fuel into the lubricating oil in 4 strokes.

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HI from the source qouted it is pointed out that this richness at low throttle openings does not mean that the engine is running rich at all throttle positions

"Then, an engine that starts without choke will give poorer mileage?
Actually, the Bullet carburettor has 4 ranges, determined by: the slow-jet, the slide cutaway, the needle position, and the main-jet, which are effective at different speeds. The mileage is determined by whichever (combination) is dominant at the riding speed. We will see this in detail when we discuss the working and tuning of the carburettor."

In some ways all the arguments about if a bike is running rich has everyone thinking that their bike is running rich at all throttle openings which will not be the case.