madass gantry system - back to cables...

marshg246 · Mar 23, 2020

joe czech said:
sorry folks. not trying to be argumentative - i'm far from having any expertise on the subject. maybe i'm not understanding all the details of what's going on, but with the madass system, it was a problem to start cold and maintain idle until the engine reach operating temp. not so much cold weather (i'm talking 75-80°F florida weather), but a cold engine. when I put everything back to OE factory - issues gone. I guess there could be something else at play here - can't say. I did not change needles, jets, or settings - everything remained the same. I do have trouble believing the amal carb folks would install a choke mechanism that has little impact on cold air or cold start operation. to me, that doesn't make sense. then again, it could be just the nature of my carbs - everything involved -- my idle circuit, float level, settings - everything coming together was driving things just a bit too lean for that perfect start cold scenario - maybe a little choke put things in balance, closer to the ideal cold start F/A ratio. I DON'T KNOW. I do know, that every time I deviate from the norm, it comes back to bite me in the arse. again, nothing wrong Don's gantry system - nice product, and I really liked the concept. fit and finish - everything top shelf. it just didn't work me. peace....

The next time you have the air cleaner off, look in the carbs and put on a little choke, half choke, 3/4 choke and see what you can see. You'll see nothing change. Then put the choke on all the way and look.

I learned long ago to not be forceful in such things - I could be missing something so, I'm not saying you're wrong, just that I cannot imagine how a choke that is not choking can do anything.

The choke definitely does something when used as designed, but 1/2 choke does nothing that I can think of.

Also, many don't realize that the choke is on when the cable is relaxed and really have it on all the time - their bikes run much better when they think they are adding choke but are actually REMOVING choke.

IMHO you should pull the chokes up, set the air screws 1-1/2 turns out and try again. Once running, blip the throttle. If it stumbles, turn the air screws in a little on both sides. When the stumble is gone, try it for a few days without choke.

Onder · Mar 23, 2020

Im still waiting for that cold 75 degree weather...

joe czech · Mar 23, 2020

marshg246 said:
IMHO you should pull the chokes up, set the air screws 1-1/2 turns out and try again. Once running, blip the throttle. If it stumbles, turn the air screws in a little on both sides. When the stumble is gone, try it for a few days without choke.

thanks - I will try that....

joe czech · Mar 23, 2020

Beach said:
Joe,
Did you sell the kit yet?

pending....

Steves · Mar 23, 2020

I don't have chokes. Temps below about 8C require a few minutes of judicious throttle to get the engine (combustion chambers) warm. When colder I start (having tickled), then tickle carbs as the engine runs first 30 seconds or so. It's a bit of a juggling act, throttle and two carbs but I have a method.

motorson · Mar 23, 2020

There must be something I'm not understanding about the Amal choke system. For me it seems to work on full choke for starting and then gets progressively leaner as I ease it off. I admit that I usually just turn it totally off as soon as I am rolling. It definitely makes a big difference when starting because if I leave it on the engine will die. Anyone here know how the Amal choke system actually does work?

Beach · Mar 23, 2020

joe czech said:
pending....

If not I would be interested.

marshg246 · Mar 23, 2020

motorson said:
There must be something I'm not understanding about the Amal choke system. For me it seems to work on full choke for starting and then gets progressively leaner as I ease it off. I admit that I usually just turn it totally off as soon as I am rolling. It definitely makes a big difference when starting because if I leave it on the engine will die. Anyone here know how the Amal choke system actually does work?

Yes! I wish you were here - it takes less than 10 seconds to show how it works!

The choke slides in a channel in the throttle valve (some call it a slide). The throttle valve has a cutaway section towards the rear of the carb - like a horizontal 1/4 moon. When the choke is full on, it partly obstructs the cutaway. Once it is lifted about 1/4" to 3/8" it obstructs nothing at idle.

marshg246 · Mar 23, 2020

motorson said:
There must be something I'm not understanding about the Amal choke system. For me it seems to work on full choke for starting and then gets progressively leaner as I ease it off. I admit that I usually just turn it totally off as soon as I am rolling. It definitely makes a big difference when starting because if I leave it on the engine will die. Anyone here know how the Amal choke system actually does work?

And, at full choke it definitely makes the mixture richer. My issue is people saying they need half choke or a little choke. When you take off full choke a little, it's still choking, but once you've moved the cable 1/2" it's definitely not choking at idle.

Tornado · Mar 23, 2020

Could it be that when fully off, the choke slider leaves a cavity within the throttle slider and this makes a difference in how the air is behaving as it goes through the throttle gap? A partially closed choke slide would change that cavity dimension and may change the air to a different turbulent flow.

Scout63 · Mar 23, 2020

motorson said:
I once asked Dyno-Dave what the trick was for getting the air filter out and in to a 1972 Commando. His reply?: "There are no tricks. There are procedures. Would you like me to list them?" Where-upon he proceeded to list the procedures starting with 1968 etc.
I learned a lot in those few moments. (Thanks Dave!)
Starting my Commando has become a bit of a "set of procedures." I'm not going to say that this works on all other Commandos but it works nearly every time on mine.

1. Tickle the carbs.
2. Set the choke.
3. Turn on the ignition.
4. Give it one third throttle.
5. Push the kick starter down until you feel compression.
6. Bring the kick starter back to the top and kick it like you really believe it will start!

Like I said, no guarantees but this has worked on other Commandos which were giving trouble starting and mine has started on the first kick in freezing weather.

Exactly the routine that works for me. I bought a linkage from Madass recently. He was a pleasure to deal with and the piece is gorgeous. I wanted to get the carbs sorted before installing it. Now they are sorted and the bike starts and runs so well I don’t want to change anything. The linkage is going in as soon as I start the next round of fettling.

joe czech · Mar 24, 2020

Onder said:
Im still waiting for that cold 75 degree weather...

it's all relative....

marshg246 said:
And, at full choke it definitely makes the mixture richer. My issue is people saying they need half choke or a little choke. When you take off full choke a little, it's still choking, but once you've moved the cable 1/2" it's definitely not choking at idle.

so, you're saying there is no beneficial middle choke or half choke - the choke design is to work either on or off. there's no "gray" area. now, that I can understand.

if that is the case, I should be able to start the bike (ambient florida 75°F) without any choke. i'll try that this AM. if that is the case and it starts without any previous issues, there must have been something else impacting my start procedure with the madass system.

not to go off topic - i'm sure I can find this, but what is a nominal idle speed (engine at temp)?

olympus · Mar 24, 2020

With the conical air filters i have fitted ... might just hag over them a piece of rag .... should give the same result

ludwig · Mar 24, 2020

Seems like a lot of fuss and extra clutter to get rid of a cable splitter.
IMO, you can better spend that money on rubber mounting your carbs.

marshg246 · Mar 24, 2020

joe czech said:
it's all relative....

so, you're saying there is no beneficial middle choke or half choke - the choke design is to work either on or off. there's no "gray" area. now, that I can understand.

if that is the case, I should be able to start the bike (ambient florida 75°F) without any choke. i'll try that this AM. if that is the case and it starts without any previous issues, there must have been something else impacting my start procedure with the madass system.

This picture is of a carb with the choke fully on. The area where the choke does something is between the black lines. If the throttle is held open a little the top black line would be that much higher. The red line is choke 1/2 on - it chokes nothing unless you are above 1/2 throttle. The yellow line is my interpretation of "a little choke" - it too chokes nothing unless you're doing about 80mph.

The choke is spring loaded downward. When there is no tension on the choke cable, it is down (choked). With full tension and it properly adjusted, you cannot see the choke when the throttle is wide open.

madass gantry system - back to cables...

maylar · Mar 24, 2020

marshg246 said:
The choke slides in a channel in the throttle valve (some call it a slide). The throttle valve has a cutaway section towards the rear of the carb - like a horizontal 1/4 moon. When the choke is full on, it partly obstructs the cutaway. Once it is lifted about 1/4" to 3/8" it obstructs nothing at idle.

You are of course correct, and for me "1/2 choke" means moving the choke lever just a hair off full so the slide is still partially below the cutaway. This gives me a richer mixture during warmup. Within a minute the engine will start to blubber, and it's time to open the choke completely. I have also noticed that raising the choke up a bit further so that it is in play again at about 1/4 throttle helps prevent bogging during really cold New England nights. Works for me.

marshg246 · Mar 24, 2020

joe czech said:
not to go off topic - i'm sure I can find this, but what is a nominal idle speed (engine at temp)?

I don't know if there is an official answer and if there is, it might not apply to each bike.

With a new set of premier carbs properly adjusted, good compression, a good electronic ignition, good gas, a clean air filter, low humidity, on the center stand, etc. you might get one to idle reliably as low as 600 rpm but I think most set them at around 1000 rpm.

I used to use 1100-1200 because I hate the embarrassment of dying at lights. Today, my Norton and Triumph twins were at 1000 rpm and my Triumph Trident was at 900 rpm when I set them. Different weather changes that somewhat.

MexicoMike · Mar 24, 2020

My Commando will idle smoothly when warmed up at 500 RPM but that's not a practical idle speed for several reasons. 1000-1100 has always been my 'standard' idle for the same reason you suggested - reliability moving off from idle at a stoplight, etc.

FWIW, if a conventional, carbureted engine can start from cold and idle smoothly with no choke or other means of enriching the fuel/air mixture, the idle system is too rich when the engine is at normal operating temperature. It is not possible to have a proper mixture when the engine is cold and a proper mixture when the engine is at normal temp without some sort of 'adjustment' that can alter the mixture for those two extremes.

marshg246 · Mar 24, 2020

maylar said:
You are of course correct, and for me "1/2 choke" means moving the choke lever just a hair off full so the slide is still partially below the cutaway. This gives me a richer mixture during warmup. Within a minute the engine will start to blubber, and it's time to open the choke completely. I have also noticed that raising the choke up a bit further so that it is in play again at about 1/4 throttle helps prevent bogging during really cold New England nights. Works for me.

Also, anyone who means turn the choke all the way on and then back off a little when they say "a little choke" are actually using a little choke. Definitely not disputing that.

I got us down this rabbit hole by asking someone to explain. You obviously understand how the choke works and your 1/2 choke makes sense. Lots of people have no idea how it works.

I even had a guy that after 40 years of riding with the choke full on and starting with it full off was amazed when I pointed out what was wrong and why he had 40 years of jetting issues! His riding experience got so much better when I removed the choke and re-jetted his carbs to standard.

bill · Mar 24, 2020

and you have again stated what i keep saying. if you dont need the chokes IT IS TO RICH.

MexicoMike said:
FWIW, if a conventional, carbureted engine can start from cold and idle smoothly with no choke or other means of enriching the fuel/air mixture, the idle system is too rich when the engine is at normal operating temperature. It is not possible to have a proper mixture when the engine is cold and a proper mixture when the engine is at normal temp without some sort of 'adjustment' that can alter the mixture for those two extremes.

madass gantry system - back to cables...

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