Choke removal

Hi there, then I am in the remove -choke league, and to plug the hole , two solutions, put an inner tube cap over the screw or a "Bic" pencil cap in the screw, cheap and safe ......less tan two cents.

My 2 cents.
My bike needs choke to start and also during a couple of minutes warm-up (even at decent temperatures).

If your bike starts and runs great without choke you probably have a rich setting allowing this to work.
And a bike with a rich setting should have higher fuel consumption, right ???

My bike runs approximately 63 mpg but requires the use of choke. What consumption do you have running an engine that works with no choke? Any difference? Trying to understand if this is theoretical only or if it is for real ?

Regards,
Per

Per, you are quite right. If the bike starts and runs without choke, it will be running rich when it gets warm, nothing theoretical about it.

debby said:

I believe the screws are 2BA and you certainly won't find those at the local hardware store!

Click to expand...

Although the carb top (and float bowl) retaining screws are 2 BA (31.4 tpi), the throttle and choke cable adjuster screw threads should be 40 tpi ("ME" thread).

While not Norton specific, this primer on carburetion summarizes the concept, I wouldn't have thought there would be so much controversy about such a basic carburetion concept:



http://roadstarclinic.com/content/view/56/96/


"A properly set-up carb will require “choke” on a cold startup, be able to pull away cleanly on half-choke within a couple of minutes and run well without the choke within about a half mile."

montelatici said:

Per, you are quite right. If the bike starts and runs without choke, it will be running rich when it gets warm, nothing theoretical about it.

Click to expand...

A properly set-up carb will require “choke” on a cold startup,

Click to expand...

But an important point is being missed, as dave M said, these Amal (MkI) carbs have ticklers?

Tickling the carbs raises the fuel level in the float bowls, therefore the engine should be fed with a rich enough mixture for starting?

Once the engine has started, then the fuel in the float bowls will drop back to the normal level, and choke may then be required to keep a cold engine running until it's warm?

Therefore as I see it, the choke shouldn't necessarily be needed for Starting'?

It would be a different matter for carbs WITHOUT ticklers.

Tickling just fills up the float bowl and the intake for a momentary richness, it doesn't change the size of any fuel circuit, the excess fuel provides a momentary rich mixture that may start the engine but if it continues to run (unless you are in Saudi Arabia at 30+C) it means that the air/fuel circuitry/mixture is appropriate for combustion in a cold engine, hence, rich for a steady state or even accelerating warm engine.

montelatici said:

Tickling just fills up the float bowl and the intake for a momentary richness

if it continues to run (unless you are in Saudi Arabia at 30+C) it means that the air/fuel circuitry/mixture is appropriate for combustion in a cold engine, hence, rich for a steady state or even accelerating warm engine.

Click to expand...

Well...I thought that's what I'd said?

However, as long as we agree that for cold starting using the ticklers is probably sufficient, and would not necessarily prove that the overall mixture was too rich if choke wasn't used.

L.A.B. said:

montelatici said:

Tickling just fills up the float bowl and the intake for a momentary richness

if it continues to run (unless you are in Saudi Arabia at 30+C) it means that the air/fuel circuitry/mixture is appropriate for combustion in a cold engine, hence, rich for a steady state or even accelerating warm engine.

Click to expand...

Well...I thought that's what I'd said?

However, as long as we agree that for cold starting using the ticklers is probably sufficient, and would not necessarily prove that the overall mixture was too rich if choke wasn't used.

Click to expand...

Except that he fails to agree to that. Only way to prove this is to start a cold bike with a choke and with the ticklers at a variety of temperatures, measure the air/fuel ratio at different points and see which works the best.

Until then we might as well talk about which oil to use. :mrgreen:

I think we have a difference in what "start" means. In a properly jetted carburetor, an initial tickled charge will allow combustion to take place (start) in a cold engine without choke, but the cold engine will stop running once the tickled (rich) charge finishes. If the carburetor is jetted rich, on the other hand it will, subsequently deliver an air/fuel mixture combustible in a cold engine and the motor will continue running without choke. However, that mixture that allowed a cold engine to run, will be a rich mixture in a warm engine. Again, there is no magic here, just basic physics.

Not about carburetion but a very good primer on air fuel mixture requirements when developing a air/fuel ratio curve digitally:


http://www.turborick.com/air1.html


"STARTING AND WARMING-UP: Abnormally or very rich mixtures are required to start a very cold engine. The air/fuel ratios must be progressively reduced from this point during the warm-up period until the engine will run satisfactorily with the normal steady-running air/fuel ratios. Starting or cranking fuel is also a temperature dependent variable with more cranking fuel required for lower temperatures. Air/Fuel ratios on initial start-up In cold weather can easily be 50% greater than stoichiometry i.e. In the 11.0:1 to 10.3:1 air/fuel ratio range."

Okay I suppose I can jump in here to throw a little more fuel :lol: on the fire;
One thing that isn't mentioned is humidity in the air. As the humidity goes up for a given volume of air the oxygen percentage goes down and since the fuel uses oxygen to burn you by default get a richer mixture. With carburetors you could actually feel an improvement in performance in the motor when you were in the rain. Oh yes and in cold weather the air is denser thereby having more oxygen and there fore needing more fuel to get the optimum fuel air ratio. Today with fuel injection the O2 sensor and computer does a pretty good job of keeping everything spot on regardless of the weather etc.
Down here in the hot and humid tropics I suppose most Norton riders subscribe to the rule; If it won't start without the choke it's too damn cold to ride

I threw my chokes on the Amals away long ago, just one more thing to fail and a crappy design to begin with. BTW Amal suppliers sell a purpose built bolt to fill the hole in the carb top for a very sanitary look.

Scooter

I think I know a bit about jetting, the bike you see in my avatar is my Yamaha TD-3 which I race. It is a 250 two stroke Grand Prix race bike which is extremely sensitive to weather ambient conditions, jetting wise. I sometimes have to change jetting it between races on a race day depending on temp, atmospheric pressure, humidity etc. I have a mini weather station and various jet sizes/needle settings depending on those factors.

But I can assure you that if you have combustion with a cold engine from tickling and it will continue to run without choke, you are running rich when the engine warms up. There is nothing particularly wrong with running a bit rich, you are just not getting maximum power and using a bit more fuel. P

montelatici said:

the bike you see in my avatar is my Yamaha TD-3 which I race. It is a 250 two stroke Grand Prix race bike which is extremely sensitive to weather ambient conditions, jetting wise.

Click to expand...

But this is a completely different animal (OK motorcycle) to a Commando! However I would certainly agree that the same rules of physics apply to both types of engine.

montelatici said:

But I can assure you that if you have combustion with a cold engine from tickling and it will continue to run without choke, you are running rich when the engine warms up. There is nothing particularly wrong with running a bit rich, you are just not getting maximum power and using a bit more fuel.

Click to expand...

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!

But the fact is, that many British bike owners, not just Commando owners (or should that be 'Amal carb' owners?) successfully run their bikes with no chokes fitted, without experiencing over-rich mixture problems which of course they ought to, once the engine has reached its normal operating temperature?

And I will repeat . If your bike runs fine when cold without choke, it will be running rich when the motor warms up, whether you know it is running rich or not. There is no way around it. Any tuner will tell you that, it is basic stoichiometry for gasoline engines. Just for fun, how far down are your exhaust pipes discolored? If further down than 2-3 inches from the exhaust port and evident at midpoint of the downward curve it is almost always caused by the unburnt fuel which tends to settle and ignite right at that point.

montelatici said:

Just for fun, how far down are your exhaust pipes discolored? If further down than 2-3 inches from the exhaust port and evident at midpoint of the downward curve it is almost always caused by the unburnt fuel which tends to settle and ignite right at that point.

Click to expand...

I think I will let you be the judge of that? (apologies for the poor photo-taken a couple of minutes ago) there is a slight gold discolouration as far as the balance pipe on each side,-but that's it.

(850 MkIII, starts on ticklers only, needs no choke, although chokes are still fitted, exhibits no symptoms of rich running, I think the pipes are about 7 years old?)

Unless it is a reflection, I see blueing right at the point where it should be with rich running. If not, what can I say, you have defied physics.

montelatici said:

Unless it is a reflection, I see blueing right at the point where it should be with rich running.

Click to expand...

It is either a reflection or some refraction from the two artificial light sources (as it's dark here in the UK -9 PM) there's certainly NO bluing on either pipe!

[Edit]I will post a photo tomorrow taken in better light.

Blue?...No.

montelatici said:

"A properly set-up carb will require “choke” on a cold startup, be able to pull away cleanly on half-choke within a couple of minutes and run well without the choke within about a half mile."

Click to expand...

This puzzles me a little when applied to the Mk1 concentric . A concentric on half-choke has the choke slide hanging halfway up the carb bore so will not be visible to the incoming air until the slide is more than half open. this is not a situation that I would expect to encounter with a cold engine. I make a point of not using full throttle for five or six miles.

If the carb had a proper choke butterfly that restricted airflow at all throttle openings or a main jet bypass such as a Mikuni then half choke would be more noticeable.

The main jet size would also seem to me to be something that should never come into play on a cold engine. If an engine is not run above 1/3 throttle when cold then richness can only be assumed at small throttle openings ?

Pilot air screw settings are adjusted when warm for smooth running.

Changes to needle jet and slide cutaway would have an effect at low openings but I have never seen a suggestion that this should be done on standard Commandos. I have 'played around' with slide cutaways and again always on a hot engine.

This no-choke aspect seems to be a Commando speciality (do Bonnies do it ?) Could it be that the shaky old Commando engine just shudders fuel past the float needle at low rpm ?

Naah!
Weak runs hot, not slightly rich. Timing out runs hot.
& as for using maximum power on an old engine, use it, that is what it is built for. Have faith.