850 MKIII Obsessive Amal Throttle Slide Synchronization Gage

Status
Not open for further replies.
Tinkerbell

Tinkerbell

Joined
Oct 1, 2018
Messages
63
Country flag
Hi Everybody,
I was lying awake even after a snifter of brandy , wondering how to synch the Amal 932 throttle slides to best advantage. So I bought a pair of cheap dial test indicators ($10 ea) off of Ebay. These are the indicators with a 3/4" horizontal arm --not the long plunger type.
I rigged them to an aluminum plate with a screw under the body of each indicator and a means of clipping them to the Amals. The tip of each indicator slides just under the edge of the throttle slide, and the screw under the body of the indicator is used to preload the dial one full revolution to zero (0.8mm) , by moving the indicator up into the slide. The throttle stop screws are backed out for this procedure.
Then as you twist the throttle you watch the indicators unwind. I had done the best job I could by eye and teeter-totter type gage under the throttle slides. When I tested this setup with the indicators, the timing side slide had moved .28mm (.011") before the drive side slide began to move.
So I tightened up the cable abutment on the drive side a bit until both indicators began to move at the same time , and they now track each other within about .03mm or 2-3 divisions on the dial which is approximately .001" .
I don't know how to get them closer unless I use a higher level of indicator with divisions of .0001" per division , but I think this is overkill on a motorcycle, and that type of test indicator has very limited total travel.
Cheers,
Kara
 
Then again, a pair of wooden chopsticks from your friendly Asian neighbour take away will do the trick with the same accuracy, cost nothing and take zero space in your toolbox...just sayin'...
 
Seems a bit of overkill to get them so close together. Would be interesting to measure the vacuum of each cylinder to see if they are the same.

You are only setting the physical relationship of the two slides. For things to be perfectly balanced there are a lot more variables e.g. ignition timing on each cylinder, valve clearances, port shapes, valve seat size, compression. Something else to stop you sleeping. :(

Ian
 
I use an electronic vacuum sync tool called the Harmonizer. These were made by a member of the Advrider forum a number of years ago. Unfortunately the creator (Grok) has now passed on. Link: https://advrider.com/f/threads/harmonizer-vacuum-multi-tool-it-aint-your-daddys-twinmax.701625/

All you do is connect it to each manifold instead of the balance hose between carbs. There should be some of these still out there because they were extremely popular at the time. On my bike I did the sync mechanically with the drill bits or chopsticks in the carb mouths, then did some minor tweaking using the electronic gauge. Also it was useful to see how the balance was just off idle and at 2-3000 rpm.

No it is not really necessary....

Russ
 
I have a TwinMax, it connects to each manifold. Mind you, I found that all it did for me really was confirm that I'd got the balance right by sticking a finger in both carbs, or using the drill bit method … That would be harder on a boxer twin as used in the demo video, I imagine … Unless you've got extra-long fingers, or your eyes work like a chameleon's.

But the OCD bit works for me … ;)
 
Last edited:
batrider said:
I use an electronic vacuum sync tool called the Harmonizer. These were made by a member of the Advrider forum a number of years ago. Unfortunately the creator (Grok) has now passed on. Link: https://advrider.com/f/threads/harmonizer-vacuum-multi-tool-it-aint-your-daddys-twinmax.701625/
Russ
Click to expand...
I bought one at the time based on the great reviews it was receiving. Haven't needed to use it yet but now I'm curious. Usually I use two same size drill bits and leave it at that .
 
Hi All,
I realize that the physical sync of the throttle slides is not the complete balancing of the twin carburetor system, however it is hard to make a case against mechanical synchronization. I understand that this can be accomplished through various worthy and effective feeler gauge methods including, but not limited to chopsticks, bleached cat ribs, or dried mouse eyes on a toothpick.
In fact it is reported that in 1964 a Norton Atlas found its way into Nepal and came into the possession of a Tibetan monk named Rinpoche Tatang. The story of how the Norton got to Nepal is fascinating as is the story of how Tatang came to visit Nepal, and all I will say here is that the reason Tatang left Tibet involved young girls. However these accounts are too convoluted to be fully recounted here. What is germane is that Rinpoche Tatang used the dried finger bones of a local species of bat to exquisitely balance his carburetors.
I admire the boots-on-the-ground creativity of all these improvised devices, but all else being equal, I really like seeing the dial indicators track each other and settle back to their respective zeros.
Now, after a somewhat brisk ride on the rough-and-ready thoroughfares of my local borough, it may very well come to pass that the magnificently balanced initial condition of my twin carburetors may have undergone some form of perturbation , and we all risk perturbation when we actually ride the apparatus. However I still retain the satisfaction and the memory that the system was set up properly at one point.
I also have the satisfaction that I have been in a battle of wits with two carburetors and come out of it relatively unscathed. It puts me in touch with our doughty ancestors who, when confronted with Twin Amals sucked wind through their teeth, screwed down their courage, and marched once more into the breach.
 
Last edited:
Balancing for all twin carbs with separate cables.

1 get the idle so each side is even as possible.

2 set the cables adjusters so each carb has the same amount of cable slack (pull cables up and down at top of each carb).

3 putt steady down a lonely street at about 2000 RPM (steady your hand by gripping the twist grip housing), reach back and cover one exhaust with the top of your shoe/foot, then switch to cover the other exhaust while listening to determine which side is louder.

4 re-set the cable adjusters with the tools in your pocket.
 
I use a jewelers saw to cut 2x4's, for framing just as the Tibetan monks do. Yeah, it takes a long time but it wastes almost no wood and I can ensure the cuts are accurate to .001. Some folks criticize me, claiming there is no need for such accuracy and saying that a circular saw is sufficient. "Pshaw!" I say!!

But when it comes to my Commando, I:

1 Adjust the slides using my finger tips against the slides and feel if they both move at the same time from the closed position

2. Pull one spark plug and leave it connected/laying on the cylinder barrel (so that it is grounded and sparks when the engine is running)

3. Adjust other carb to idle at 500 RPM

4. do the same on the other side - adjust other carb to 500 RPM.

5. Reinstall the plug, start bike. Idle will be about where I want it.

The Tibetan monks don't do it that way but the Benedictine nuns do. Sister Mary Amabelia smacked me up the side of the head with a ruler many years ago until I finally got it right. ;)
 
I use a tuning fork, as the slider binds slightly in the carb when you pull on the go faster you get a change in tone. I then check both carbs are in tune at various stages of throttle opening. It saves fuel!
 
On my commando I have twin 32mm concentrucs and a 32mm ID balance pipe
But I found the tickover a bit high so I've disconnected one of the carburettors and now the bike runs spot on
No more balancing for me, i call it the "mikuni hunter"
 
Hello fellow Norton Enthusiasts,
Dave, whose moniker in this august forum is Cash, informed me of a fatal flaw in my most elegant apparatus designed in the service of balancing my wayward Amal carburetors. He pointed out that the counterbores into which the throttle slides settle, in the absence of stop screws, are found to vary in their respective depths.
Thus I was measuring a difference of movement from two different beginning apertures. I proceeded to locate a pair of drill bits of an appropriate diameter, and soon found that there was a good .020" difference between the throttle slides, relative to the bottom of the bore, which is truly the important quantity at issue here. Sadly, my apparatus can only be used effectively to verify what feeler gauge technique has already revealed, and with carburetors mounted on the engine, I do not see a way to overcome this limitation.
However, all is not lost. Dial indicators are a valuable tool in the setup of my Trident clutch mechanism and the hard won experience of setting Norton carburetion has prepared me for my encounter with T150 carburetion , whose three carburetors and gantry mechanism at this very moment await me on my bench.
Now, it is a fact that this winter I plan to renew the bushings and bearings in the MKIII gearbox--but I could not bear the thought of not having a single working British motorcycle on the premises. Thus I came up with the idea that I needed a simple and reliable bike to tide me over whilst repairs proceeded on the Commando.
Obviously the only sensible solution was to obtain a 1973 Triumph Trident. I was so bold as to buy a bike from Prescott Arizona, and have some nice people with a truck deliver said machinery here in Vancouver Wa. The bike and I had never met before. Now, the bike looks to be in showroom condition, and the P.O. claimed that the motorcycle ran perfectly . While I believe this statement was offered in good faith, it had overoptimistic elements contained within its scope.
The clutch needs some fine tuning, and appropriate renewal parts are en route from Athens, Greece. It turns out that Tridents are all the rage in Athens. And carburetor renewal parts are in the process of being installed this very day. The third issue is to find a way to stop the three cylinder monster from kicking back during the starting procedure. I have a bruise the size of a coffee saucer on the side of my knee. I am only flesh and bone, and the bike is made of steel . I suspect I may be dumping the Boyer unit in favor of a Trispark soon-- if kicking behavior does not improve.
However, after obtaining appropriate ear plugs I took some rides on the Trident-- before removing its carburetors of course. It is a very different kind of creature relative to the Commando. It is a trippy machine. Many times I have gotten down behind 500ug of high quality LSD , and I can say that riding the Trident is its mechanical equivalent .
Sincerely,
Kara Elizabeth.
 
Tinkerbell said:
Hello fellow Norton Enthusiasts,
The clutch needs some fine tuning, and appropriate renewal parts are en route from Athens, Greece. It turns out that Tridents are all the rage in Athens. And carburetor renewal parts are in the process of being installed this very day. The third issue is to find a way to stop the three cylinder monster from kicking back during the starting procedure. I have a bruise the size of a coffee saucer on the side of my knee. I am only flesh and bone, and the bike is made of steel . I suspect I may be dumping the Boyer unit in favor of a Trispark soon-- if kicking behavior does not improve.
However, after obtaining appropriate ear plugs I took some rides on the Trident-- before removing its carburetors of course. It is a very different kind of creature relative to the Commando. It is a trippy machine. Many times I have gotten down behind 500ug of high quality LSD , and I can say that riding the Trident is its mechanical equivalent .
Sincerely,
Kara Elizabeth.
Click to expand...

I put a TriSpark on my Trident years ago and never looked back. I also added electric start and never looked back. Guess I'm what the British call a braces and belt guy.
 
Status
Not open for further replies.
Back
Top