New Amal 932 carb adjusting

Joined
Aug 26, 2019
Messages
34
Country flag
I just installed a set of brand new Amal 932's on my 73' 850 Commando. After watching numerous videos and reading various posts I've come to this as my adjustment strategy...

1. After warming the bike I'll back out the idle screws (diagonal) to a low rpm.
2. With my air/fuel screws (horizontal) set at 1 & 1/2 turns when I started the bike, I'll back them out until I get the highest rpms and further turning makes no difference. Then I'll turn the air/fuel screw in very slowly until I hear a slight decrease in rpms, then back slightly to just before the decrease - repeat on other side.
3. My idle should still be high so I'll adjust out the vertical (idle) screws until I achieve a steady idle around 1300 rpms.

Correct? I live at sea level if that matters.
 
Joined
Aug 26, 2019
Messages
34
Country flag
I just installed a set of brand new Amal 932's on my 73' 850 Commando. After watching numerous videos and reading various posts I've come to this as my adjustment strategy...

1. After warming the bike I'll back out the idle screws (diagonal) to a low rpm.
2. With my air/fuel screws (horizontal) set at 1 & 1/2 turns when I started the bike, I'll back them out until I get the highest rpms and further turning makes no difference. Then I'll turn the air/fuel screw in very slowly until I hear a slight decrease in rpms, then back slightly to just before the decrease - repeat on other side.
3. My idle should still be high so I'll adjust out the vertical (idle) screws until I achieve a steady idle around 1300 rpms.

Correct? I live at sea level if that matters.


Correction - not 932, but 930 Concentric
 
Joined
Apr 29, 2009
Messages
1,233
Country flag
Someone correct me if I am wrong but I thought all 850's used the 932 carb. 32 mm ports on the rh4 head and 30mm ports on the rh10 head with 32 to 30 tapered inlet manifolds. Sounds like the proceedure is correct. Amals are opposite a lot other carbs, turning the idle mixture srew out leans the mixture and turning it in richens it. Make sure the bike is well warmed up. Generally if you get the idle right on a cold engine, it will be too rich when it warms up. 1300 rpm is a little high, I would shoot for 1100. Did you synch the slides. I use the drill bit method explained here.
 
Joined
Apr 27, 2015
Messages
1,630
Country flag
The idle air screw has about a half of a turn where it seems to do NOTHING... The reason that happens is because across that half turn, your engine will idle temporarily in a similar manner as you turn the air screw in or out until it runs out of the workable A/F ratio acceptable range... from too lean until it gets to too rich to run...

So that half turn "dead spot" seems to mean that the screw position is OK anywhere in that range, but that is NOT true....

The reason it isn't true is because when you lift the throttle, the next element of carburation enters the A/F ratio, and since the first element is still in play (The idle air screw position) you want to bias it's position to offset any deviation caused by lifting the throttle, so what you end up with is both a steady idle AND a smooth accelleration as you lift the throttle...

So, You find the starting position for the idle air screw midway between the lean and rich stumbling points. Then you lift the throttle to 2000 rpms and lower it back down, then you turn the air screw in a very small amount and lift and lower again listening for the smoothest accelleration. You keep going, even if you go past the smoothest spot and have to come backward to it. Then you do the same to the other side.... Then go back and micro adjust both sides as you lift and lower the throttle...

This adjustment pays off in that you've adjusted your bike to remove any stumbling caused by a wavering A/F ratio caused by lifting the slides to accellerate, so you are less likely to cough and die pulling away from a traffic light...
 
Joined
Aug 26, 2019
Messages
34
Country flag
Someone correct me if I am wrong but I thought all 850's used the 932 carb. 32 mm ports on the rh4 head and 30mm ports on the rh10 head with 32 to 30 tapered inlet manifolds. Sounds like the proceedure is correct. Amals are opposite a lot other carbs, turning the idle mixture srew out leans the mixture and turning it in richens it. Make sure the bike is well warmed up. Generally if you get the idle right on a cold engine, it will be too rich when it warms up. 1300 rpm is a little high, I would shoot for 1100. Did you synch the slides. I use the drill bit method explained here.

Great stuff - thank you Your're correct about the carb sizing. I miscorrected myself. Also, I finally found a mech here in San Diego that knows his way around a Norton - I'm going to him for the carb work / training.
 
Joined
Aug 26, 2019
Messages
34
Country flag
The idle air screw has about a half of a turn where it seems to do NOTHING... The reason that happens is because across that half turn, your engine will idle temporarily in a similar manner as you turn the air screw in or out until it runs out of the workable A/F ratio acceptable range... from too lean until it gets to too rich to run...

So that half turn "dead spot" seems to mean that the screw position is OK anywhere in that range, but that is NOT true....

The reason it isn't true is because when you lift the throttle, the next element of carburation enters the A/F ratio, and since the first element is still in play (The idle air screw position) you want to bias it's position to offset any deviation caused by lifting the throttle, so what you end up with is both a steady idle AND a smooth accelleration as you lift the throttle...

So, You find the starting position for the idle air screw midway between the lean and rich stumbling points. Then you lift the throttle to 2000 rpms and lower it back down, then you turn the air screw in a very small amount and lift and lower again listening for the smoothest accelleration. You keep going, even if you go past the smoothest spot and have to come backward to it. Then you do the same to the other side.... Then go back and micro adjust both sides as you lift and lower the throttle...

This adjustment pays off in that you've adjusted your bike to remove any stumbling caused by a wavering A/F ratio caused by lifting the slides to accellerate, so you are less likely to cough and die pulling away from a traffic light...

Incredible help here - Thank you very much. You're correct about my bike dying at signals... when I turn the throttle it seemed to flood so much air, so quickly, it dies. Maybe this new mech can help solve this - but I'll try your method first.
 
Joined
Apr 20, 2011
Messages
4,801
Country flag
The idle air screw has about a half of a turn where it seems to do NOTHING... The reason that happens is because across that half turn, your engine will idle temporarily in a similar manner as you turn the air screw in or out until it runs out of the workable A/F ratio acceptable range... from too lean until it gets to too rich to run...

So that half turn "dead spot" seems to mean that the screw position is OK anywhere in that range, but that is NOT true....

The reason it isn't true is because when you lift the throttle, the next element of carburation enters the A/F ratio, and since the first element is still in play (The idle air screw position) you want to bias it's position to offset any deviation caused by lifting the throttle, so what you end up with is both a steady idle AND a smooth accelleration as you lift the throttle...

So, You find the starting position for the idle air screw midway between the lean and rich stumbling points. Then you lift the throttle to 2000 rpms and lower it back down, then you turn the air screw in a very small amount and lift and lower again listening for the smoothest accelleration. You keep going, even if you go past the smoothest spot and have to come backward to it. Then you do the same to the other side.... Then go back and micro adjust both sides as you lift and lower the throttle...

This adjustment pays off in that you've adjusted your bike to remove any stumbling caused by a wavering A/F ratio caused by lifting the slides to accellerate, so you are less likely to cough and die pulling away from a traffic light...
I have found a easy way to get the fuel/ air mixture 100% correct on tick over , I just brought a second hand Gunsons Colourtune kit, but whatever you do with it, don't attempt to try it in broard daylight I always use mine at night time. Any one who is not colour blind could get the mixture right .
 
Joined
Apr 29, 2009
Messages
1,233
Country flag
What idle jets did your carb come with? Many suppliers fit them with #17's. These are generally too lean and #19's need to be fitted especially on 850's. The idle jets are the cross head screw on the opposite side of the carb from the mixture screw. Remove one carb and unscrew them to see what you have. The sizes are identified by rings on the jet. Two rings are 17's, three rings are 19's.
 
Joined
Apr 27, 2015
Messages
1,630
Country flag
Incredible help here - Thank you very much. You're correct about my bike dying at signals... when I turn the throttle it seemed to flood so much air, so quickly, it dies. Maybe this new mech can help solve this - but I'll try your method first.
As you can see Chris, some people think that the idle adjustment as a separate thing to set statically and use a "colortune" to set the static A/F ratio. The problem with that method is that lifting the slide can cause the A/F ratio to deviate on some bikes, so if the bike stumbles when you accelerate, then what good is having the perfect A/F ratio at idle...

Since your other components are basically fixed, (but not actually if you wanted to shim your jet needles to micro adjust them between the fixed positions on the needle among other creative adjustments) the idle air screw can be biased to offset the throttle lifting induced stumble...

I did that adjustment for a friend's commando who complained about his occasional stumble off idle and he was surprised how the stumble went away with a few minutes of adjustment using my method and paying attention to the engine response while lifting and lowering the slides repeatedly as the idle air screw is micro adjusted.

The proof of what I propose is generally shown on a dyno chart read out which shows both the power curve chart and the A/F ratio charts. You'll notice there's generally a blip in the A/F ratio when the acceleration begins. If your idle A/F ratio can be biased to help to keep the blip inside the workable A/F range as the bike transitions to the needle/needle jet dominant influence then you get no stumble between the idle and the secondary elements of carburation, albeit your colortune may now indicate your idle A/F ratio is off it's most optimal proportions for idling.. but the bike will still idle.

Some people set their idle air screw in the mid point of it's workable range and the get no issue with stumbling when they lift the throttle. There's a lot involved in why they don't get a stumble and others do get it. Maybe fuel level height or how tight their slides are to their slide bodies, or some other thing.

I hope the adjustment method works for you
 
Joined
Apr 20, 2011
Messages
4,801
Country flag
My comment regarding the Colourtune is of course subject to getting the ignition timings right and having the correct pilot jet , that is not blocked in any way and the correct throttle slide , needle jet and needle. The suppliers of the new Amal carburetors appear to be no help in putting the wrong pilot jets with some new carbs.
It should be used at a constant revs, opening the throttle automatically injets extra fuel/air into the combustion chamber.
 
Last edited:
Joined
Apr 27, 2015
Messages
1,630
Country flag
I wasn't trying to knock the use colortune. I just wanted show that the reliance on it, without understanding the relationship between a statically set idle A/F ratio, and what happens to that A/F ratio when the slides are lifted, can lead to the conclusion by some that their idle air screw position is "well set", when the bike might accelerate more smoothly with a micro adjustment using the technique I discribed...

I wonder if you can do that lift and lower the throttle technique with colortune?? Can you?

,
 
Joined
Apr 27, 2015
Messages
1,630
Country flag
No, I recalled you can't actually rev the bike up with a colortune, but can you use it in the lower rpm range other than just idling?
 
Joined
May 7, 2005
Messages
4,388
Country flag
The colortune can't be used under load but can be used to check the throttle slide cutaway by watching the colour as the throttle is opened.
 
Joined
Apr 20, 2011
Messages
4,801
Country flag
Colourtune can be used to 3000 revs, but remember this is not putting an engine under load. Sometimes one can detect a low speed misfire that is hard to detect by hearing on tickover, as I have done. (One faulty suppressor cap)
 
Joined
Jan 31, 2010
Messages
2,166
Country flag
"I wasn't trying to knock the use colortune."

No, you weren't....so I will!

Colotunes are designed to be used to (allegedly) set the idle mixture which is the easiest thing to set anyway - no equipment needed at all to do so other than a screwdriver and your eyes/ears. You can't use it under load, where all of the other carb settings that are much more difficult to determine need to be tested and then adjusted - main jets, needle jets, needle height, etc.

How an engine operates best in reality and what may be the optimum "color" for a combustion chamber burn at idle are totally dependent on the specifics of the timing, carburetor, cam profile, combustion chamber shape, engine temperature, spark plug, RPM, etc etc etc. IOW, one engine could idle very smoothly with the "correct" color while another will not.

So, adjust the various settings to produce the best response from the engine itself; sell the colortune on Ebay.! ;)
 
Joined
Jan 10, 2020
Messages
97
Country flag
A colortune is a useful tool and can certainly help if you are trying to make sure you are close. The ultimate running of the bike is the goal so as long as you have that in mind I think they are a great check. People that have been doing things for 100 years always knock the use of tools that are perceived as cutting it short because they can be used to forego understanding which certainly won’t help - but if I were just starting out I’d try the method of adjustment as detailed elsewhere then check it with the colortune. It saves a ton of second guessing and frustration for a beginner. If it runs well off if idle you know it’s all set. It’s a neat tool I keep one around.
 
Joined
Apr 20, 2011
Messages
4,801
Country flag
Put 10 different amateur mechanics on setting a pair of Amals up you may get ten different settings.
Used correctly, with the right ingition timing and pilot jets etc a Colourtune cuts out any second guessing.
 
Top