tricky amals

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May 2, 2005
my '73 850 runs pretty decent but will occasionally die when i pull up to a light. the idle just conks out unless i blip the throttle. strange thing is that when i give her the old kick in the morning, great running. but a little mild use and idling becomes dicey. im running original amal's with the pilot screws set at 1 1/4 turns out. idle is normally around 1000rpm. any advice? things to check?
First thing to check if your cutting out at stop signs is the Battery. You should be able to start the bike warm it to point that it will idle then turn on the head light and hit the brights. Still running? Hit the rear brake that light may send your voltage below the ing. requirments. A bike that idles at 1000 rpm doesn't die when rolling to a stop because of carbs. norbsa
Something to consider with Amal concentrics: How often is the bike used?
I have found with all my carbed bikes(amals and Del orto's) that infrequequent use allows modern "gasoline" to slowly build up deposits in the idle circiut that slowly makes the mixture richer. on amals you may have to remove the idle mixture screw and ream out the jet to remove the deposits(they're quite hard!) be careful the jet is only .017" dia..

The use of Chevron Techron fuel system cleaner (a snake oil that works) about every 4 months will help reduce the build up. Use 1/2 bottle with a full tank of gas and ride for about 100 miles will usually make things better. :wink:

Bill Edwards 75 Norton,74 Trident,77 900 Ducati,76 BMW R90S
thanks much for the replies. to give some more information: i ride my norton at least once a week and run it with leaded gas. i never even thought about electrics but my headlight only works in high mode and my right side blinkers dont work at all. i'll fix those properly and start testing...

thanks again
The problem at stop lights is the Lucas alternator barely puts out enough juice to operate the engine. The small draw of the brake light is enough to kill the engine. If you are running a Boyer, it's worse.
This is why you need a strong battery.
At idle, you are pulling from the battery. Once under way, everything is fine.

Even the high output RM23 alternator does not put out enough at idle to keep from drawing on the battery.

This is why people convert to 3 phase units. It generates more power at a lower RPM.

Keeping a strong battery solves the problem.
interesting...thanks for the heads up. I'll check my battery and then figure out how to beef my the charging system. who makes the 3 phase alternator?
If you are still running points, check the resistor buried up under the little u box where the condensors are. I had one with the wire burned through at one of the lugs. It ran fine most of the time but would just die occasionaly till I found the problem. Switched to boyer after that. Another good idea is to bypass the power to the handlebar kill button which you never use anyway. There is a spare wire lug on the ignition switch that can be used to provide power.
Don't disconnect that kill switch!
What happens the next time you have that baby go over, due to any number of dumb reasons?
Last time, during parking, it was my boot got stuck in a space between cobblestones. The boot stayed, the bike rolled forward. I had no foot to hold the bike up with, it went over on top of my foot. Naturally, it continued to run, and the clutch was already pulled and it was still in gear. Couldn't let the clutch go, couldn't get it out of gear, couldn't reach the key, and still hoped to hold it up enough to avoid denting the tank. Prime case for a kill switch.

Check your battery, all my weak idleing problems went away with a new battery, even starts much better. Boyers need a strong battery.
3 phase

I only know of two, there may be more.
The Lucas 180w. RM24, and the Sparx 220w.

Just so you know. I have owned several Nortons, tempted as I may have been, I have yet to put in a 3 phase. A strong, properly maintained battery has always corrected the issue. If I find the need to change a stator, rectifier or zener, I may change it out and keep the remaining parts for spares.

Also, as I replace batteries, I am going to sealed units.

Another train of thought which I would suggest ~ have you checked your carbs.. that is wear factors.. what sort of mileage.. etc ..

I replaced the Needle jets in my amals and that was a huge improvement on all aspects of idling and performance.

(It is a common scenario for these babies to wear out in 10-12 k . )

I also replaced my carbon plug leads with copper.. another huge fix for me... (mine is Mk I boyer.. )

It is very possible there is an accumulation of small problems such as these.

For example my first experience with worn Amal slides was on my BSA OIF Lightning and it would idle badly or erratically ~ .. I know this in hindsight was the worn slides..
thanks all,

im still running points and havent done too much poking around the electics--definitly not my strong point. I really suspect electric though because the problem is erratic. in my driveway the bike idles great. just when i happen to cruise well beyond pushing distance (or am in heavy traffic) the bike will conk out. I've got some direction on stuff to check so I'm pretty sure I'll make some progress.
Hi people!

Well, I have exactly been experiencing the same sort of problem on my 750 S, lately...
It was running absolutely perfect for the past 1000 miles, starting first kick with a healthy idle and beautiful powerband. But now it dies when I need to stop at traffic lights. Though I try hard avoiding Traffic lights.
First I thought it suffers overheating problems while being taken through rushhour-traffic accidently. I changed Sparkplugs and it started first kick again, no problems. Then it died away again. No chance of starting it.
The Amals seem to be in fine condition, not worn out definately.
So I will check the battery, according to your comments. And the Boyer Bransden, as well.

What else?

Thank for your replies!

Matt from Hamburg
'89 BMW R100GS, '69 Commando 750 S
Hi Matt,

When you replaced the spark plugs, did the old ones both have a sooty black appearance? Or was only one plug sooty?

Did you observe the spark of the new plugs prior to installing them? If so, did each produce a fat blue spark? (Note: I stole this descriptive terminology from Debby)

Did you check all the connections on your Boyer ignition? Many forum members have reported problems with the electrical terminations/connections on electronic ignition systems.

In addition to checking the battery, you shlould check the output of the alternator.

More clues would be helpful.

Hi Jason!

Thanks for your reply. Well, both sparkplugs had a ”sooty black appearance” indeed…

Seems like the problem likely seems to be anything BUT the battery? Am I facing the same problems as Debby?!? Or someone else?!?!?



Other than idle does it run ok? And did the problem suddenly develop or did it get worse gradually? Maybe all you need to do is go through the idle adjustment procedure (assuming you haven't already).

Hi Debby!

Good to hear from you. Well, my Norton idles at a steady 1000 rpm. This problem just started suddenly right after I went out on a ride with my friends. The bike ran just fantastic then, pulling in every gear, from 3000 to 5500 rpm. It was such a blast, as this was the first time after running in, where I gave it some go.
The alternator seems a little weak, because riding in the dark with the lights full on, it dies when pulling up. But that problem is known to all of us, isn’t it?

The problem is: It always starts first kick, idles perfect, then dies… and won’t start again.
It dies away when the engines warm, it dies when it’s cold. The problem occured all of a sudden, not gradually.

Thanks for all your input!
When you try to restart it does it try to fire at all, if it does is the firing seem to be on one side only. What components have you swaped out or swaped between sides.

Problems I have had which seem similar is a coil that gave up only when warm, but it only affected one side.
Hi kommando!

The bike has been overhauled from the ground up, before I bought it, i.e.
completely torn apart and built up from scratch. The whole process is being documented via Photos, Partslist attached (PROOF!).

The points ignition system was replaced by a Boyer Bransden for less fettling (well, I can see it coming...).

I will check the coils as well, then (sigh).

At least, the Norton gave me nothing but joy for months and now it is time to get into the depths of machinery...

Anything more?
Sudden onset sounds more like electrical not carbys. If the shop installed the boyer maybe they didn't do that fix to the pickup wires :?: Perhaps that's all it is...

Matt, Check your choke lever. Sometimes the lever loosens, partially closing the chokes. The lever should be all the way to the stop. If it won't hold it there, tighten the tension screw.
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