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Jan 27, 2008
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I've re-assembled my 850 after probably 20+ years of not running, and at least a few years fully dismantled. It was a challenge to put something together without having taken it apart, but I think I did OK.
I started the bike six weeks ago, and had many issues - oil leaks, mis-wired ignition switch, shifter quadrant off by one tooth, bad Boyer box, un-tunable carbs, melting gas tank, etc.

Most of the oil leaks have been resolved, wiring fixed, quadrant re-aligned (diagram in the manual is a little misleading, IMO) and carbs and gas tank replaced.

I just got back from another shakedown cruise, and still can't quite get the Amals tuned. I tried to start it this morning, following the procedure of: tickle the carbs, cycle once or twice, partial choke, ignition on, kick. Remove plugs, cycle the engine to clear flooding, repeat. After 1/2 an hour, I gave up and went for a little 80-mile ride on the Speed Triple. When I came back, I pulled the Norton out, tickled the Amals, and it started on the third kick. Idle is uneven, pilot air screws don't seem to do much - it seems to run best with them run all the way in.

I've balanced the carburetors with a mercury stick, I've balanced the throttle and choke cables, I've pulled the Amals apart and checked for burrs in the pilot holes (one was burred up), petcocks are clear and free-flowing, fuel lines are new, tank is new, timing is checked with a strobe. When I ran the bike this afternoon, I tried the manual procedure of balancing each carb independently by removing one spark lead at a time. It ran OK on each cylinder, but not the way I feel it should.

Its been 25+ years since I last had a bike without a button, but I'm nearly at my wits' end. Do any of you have suggestions?
Bill, I have a six page amal tuning guide I could email to you if you would like.

In addtion to tuning, make sure that the carb to intake and intake to head joints/bolts are snug and not leaking. Do not overtighten these bolts though.
I had a problem with a slide sticking open(1500 miles after resleeving) on one carb of my 650 Norton. It would do this intermittenly, aobut one time in four throttle openings.
I fiddled with the cable and thought that I had it.
It wasn;t that, it still wanted to stick.
I decided to take the carb off and have a look to see if there was a burr or crud in the slide bore that was causing the probem.
The moment that I tweaked the first bolt loose I heard a pop as the slide dropped back down onto it's idle stop.
I had overtightened the inside carb bolt and this was distorting the carb body, that is why the throttle was sticking. With a new tight slide in the carb it didn't take much distortion to cause the sticking.
I tried it several times and for that carb the bolts can only be brought up just snug, any extra little tweak and the body distorts causing the slide to stick. At the same time distortion is occuring to the carb body, no doubt the flange is distorting too. This can cause leakage at the joint and the resultant week/variable mixture, poor starting, poor idling.

I was amazed at how little wrist effort it took to make the carb body distort. Something to check anyway.

Let me know if you would like the tuning guide.
The carbs not responding to air screw adjustments is a sure sign you didn't run a.016 drill bit into the idle jets. This tiny drill bit must be epoxied into the end of one of the plastic tubes that come with a brake clean can. It's about a 1 1/2 reach down a small hole behind the air screw to get to the little brass jet. A .016 drill bit is a #78 bit gluing it in straight is a bit fiddly. but mine is used weekly over the years. Have you checked the float heights to make them a pair at the 2MM speck? Float hight effects all the jets in the carb. These two things should be the first two things you do when you work on the carbs.
worntorn said:
I was amazed at how little wrist effort it took to make the carb body distort. Something to check anyway.

Amen to that. Had the same on my bike.

Can anyone expand on the procedure to clear out the idle jet with the 78 bit?

I have my carbs currently soaking in cleaner but would like to make up the rig described above to clean this damn thing befire I go putting them on again.

OK so the drill bit is glued firmly in the little red plastic tube dried over night. We don't want it coming out inside the carb.
You will be putting it into the hole in behind the air screw. Now the jet is pressed into the body and a bit this size formed the hole in the middle. The hole is small as is the bit but if you twirl it as you slowly proceed you will feel it hit the dirt in the hole. Twirl it constantly pushing very lightly. You are re-drilling a hole about 1/8 deep on a good carb the hole will fit quite snug on the bit. Now spray it out with brake clean down the air screw hole. Blow out with compressed air if you have it. Have you set your floats?
Worntorn, I'd like to see your Amal tuning guide. If you'd email it to me, I'd appreciate it. I'm sure you can PM me, but here's my email:

Norbsa, I didn't run a drill bit into the pilot jets. I did blow air through them, but after studying the sectional illustrations, it looks like the only way to ensure a clear pilot jet is to do the drill bit thing. I did check the float levels. They looked good and equal. Carbs are new, and the nylon floats look to be pretty good molds - no visible warp or deformation.

After posting this thread, I went out in the garage, started it up, and spent about an hour and a half riding around my town - first just in the neighborhood, then a larger radius around the neighborhood, then finally all over town. Stopped for gas, and it started right back up. Still not quite right, but definitely better.

Bike currently is set with the throttle screws about one turn in from contact with the throttle valve, and the air screws at 1/2 turn. I'll try checking the jets in the next day or two. Everything points to a weak idle circuit mixture.
Symptoms you describe could be worn, leaky slides. You say the carbs were replaced. Do you mean they are new? Have the slides been sleeved? I would not try to tune a bike with Amals that have not been sleeved. I was pulling my hair out trying to tune the twin Amals on my Commando when I first acquired the bike. Could never get them to idle properly. Eventually gave up and went to a single Mikuni. Most of my other bikes have Amal Monoblocs and all are sleeved. Makes a huge difference and gives you a good solid starting point for tuning.
The best way I have found to clean carbs is to boil them in soapy water. The boiling action removes any foreign matter from all of the passage ways. I set up a small tin pail over a propane stove.

Take the carb apart as much as possible then put everything in the boiling water. After five minutes of boiling, everything should be clean and you can remove the carb body with tongs. While it is still hot hit it with compressed air to remove any water that might be in the passage ways. With the compressed air on it, the hot carb body will dry completely in a minute or so. Do the same with the other parts.
When you boil water the minerals fall out. If you want to go another step to extra squeaky clean carbs, i would use distilled water so things don't get left where they aren't intended.

I also would love to see your Amal tuning guide. Not sure if it can be made available to the masses via this site, but if not , my e-mail address is

They suppose to be simple carburators but I have a challenging time getting them properly adjusted.
Thanks in advance,

Josh, Calgary, Alberta
If anyone else would like the tuning guide please let me know, I can email it to you. You can either pm me or leave your email on this thread as Josh and Bill did.
dezwartj said:
I also would love to see your Amal tuning guide. Not sure if it can be made available to the masses via this site

There's a lot of Amal tuning information on the Hitchcock's (UK) website: ... nc_ht.html

And Bushman's website tuning info:

Amal carb info link from the Norton Commando home page:

And I will add those links to the Commando forum page useful information sticky topic, so they remain easily available:
I'm tuning the concentrics on the 650 right now and trying to find out what the correct float position should be with downdraught carbs. I thought one of the items L.A.B. posted might explain, but all I found was this
"For down-draught carbs that slope down (i.e. on Atlas), the setting will need to be adjusted to suit using other methods."

Nor does my six page Amal tuning guide give any details on sloping carbs.

Any ideas?

BTW, L.A.B. please email me if you would like to add the tuning guide I have to the list of Carb info. I'm not sure how to put it on the site by any other method.

Well I boiled the carbs, adjusted the float level and my left carb is now firing at idle albeit it is not a smooth idle like on the right side. Seems like my last option is the #78 drill bit trick.

Can the idle be cleaned out while still on the bike or is it best to pull the carbs again?

Thanks again fellas
Yes I do it every year. Or as found necessary. A little of the brake cleaner will find it's way into the air cleaner but it just flashes off. This is a first step not a last step.
In response to some questions, I put two brand new 932s on the bike, jetted for the 850. I am convinced that the pilot jets are burred up or somethng, as the air screws seem to have little effect. It runs OK with the air screws either tight in or out 1/2 turn. More than that, the bike starts to stumble. There doesn't seem to be any vacuum leak, as the mercury level on my carb stick was pretty good (about 28 cm). I'll be getting a couple of #78 twist drills as soon as I can get to the supply house.

Once the revs come up enough to transition the carbs from the idle circuit to the main jet, everything's fine. Unless I'm mistaken, this means decent fuel flow and proper jet range for the main circuit, but the idle circuit is running lean.

With the air screws set at 1/2 turn, and the throttle screws set at 1 turn past initial contact, I was able to start the bike today without too much trouble (about ten kicks).

Once warmed up, I took it out for a 100-mile ride, with several stops, and each stop only took 1 or 2 kicks to start up. Only mishap today was the right foot rubber falling apart (dry rot).
BillT said:
I was able to start the bike today without too much trouble (about ten kicks).

A properly tuned Commando with a strong battery should start within 3 kicks.
Keep wotking on it.
I've had good luck using a twist tie from a bread wrapper to clear the jet. First burn the paper of the twist tie with a match, pull it through your pinched fingers to straighten it out, then poke around inside the hole with the air screw removed. I've measured the thickness of a number of different twist ties at .0165" . They are made of a soft wire & shouldn't harm the jet. After poking the wire through the jet, I give it a blast with aerosol carb cleaner. A little easier for me to find than a #78 twist drill or a banjo string.
I picked up a couple #78's from a hobby shop if you can't find it at a house. Something that deals with planes rc cars etc.
Did mine up tonight with the #78 bit and the bike seems to be idling a bit better but at this point any loping is probably just my ears not syncing right. She kicks over first or second with a good tickle.

What are you guys idling at?
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