Any Ideas ?

Hi, I am new to the Forum and have owned several Norton Commando's. The problem I am trying to solve is the bike starts and runs perfectly while on the center stand then when I lower the bike off the stand it runs rough and stalls. It can idle around 700-800 rpm and ticks over nicely and runs smooth thru all RPM, rock the bike off the center stand and it stalls.
I have checked the harness, carbs are new Amal Premium 930, new plugs, timing checked, valve clearance, etc. Any Ideas?

Cheers.

Hi Norto
Welcome to the forum.
Boyer or Points????
If Boyer then check wires at the Pickup in timing side. Check wires and connections at handlebar switchgear. Look at kill switch in particular.
Looks like the moment you get bike on Isolastics the bike quits. I would look electrical. Also look at hightension leads at coils (sparkplug wires)
Troubleshooting is sometimes hard to pinpoint but here is my two cents worth.
Cheers,
Thomas
CNN

Thanks for your reply! It is a Boyer ignition and as you mentioned it seems electrical to me. New high tension leads, no kill switch - just ignition switch.

Did this start when the carbs were installed? Float levels too high. Jim

Maybe run a dedicated ground wire to the head via a headsteady mounting bolt to the plus side of the Batt (positive Ground).

New carbs had 60 miles on them before it started and ran fine. All was good.... rode the bike 10 miles got home and went to start the bike again and it started fine on the stand, lowered the bike off the stand and ran really rough and would not idle, just stall. Checked float levels and cleaned idle jets.

Seeing how your Kill switch is bridged out , I now agree with CanukNortonNut .
With the bike running nicely on the mainstand , gently pull downwards on the wiring where it exits the casing at the back of the points cover , (to simulate the bike coming off the mainstand ) .
The loop in the wiring which should be hanging downward before it goes up the frame tube is where the wires inside may be broken , and only causing the fault when the wiring is minutely moved due to the bike settling on the front Isolastic.
This area of the ignition wiring is subjected to huge vibration across the Isolastic connection .
The problem may be at the connection of the wiring onto the back of the pick-up plate where the wiring is soldered on also .

When you replace the wiring in this area , (if you need to) , remember to leave a nice large loop of wire hanging downwards ,where it exits the pick-up , before it gets cable tied to the frame tube , this will distribute the stresses over a greater length of wire and reduce the chances of it happening there again .... not to say it aint going to happen somewhere else though.

My problem ,,,,,,,,,,,similar to your own , after many many hours of searching , was the Bloody Kill Switch.
These are the reasons we love our Nortons , they keep us interested .
regards Supaflee

Definitely sounds electrical - being vibed to conduct in one condition but intermittent at other vibe states. I'd suspect brake & horn wiring to investigate next all the way from switches to the devices and never forget the intermittent kill button. Some electronic ignitions will fire on make-breaks or sudden volt drop from a short that sucks down an instant, so one worship ritual for me is bowed down maybe even on knees in dim light plugs out on head tugging bumping jerking to bashing strutures hoping for flash of inspiration. If engine responsive to pilot air screw extremes then float level is adequate to run fine full range on stand or tires.

Sounds like everyone is pointing toward electrical. I had the exact same thing happen on an Atlas years ago. Turned out to be a loose fitting blade type electrical connection. It was facing downward and the drop off the stand would separate the connection and the stiffness or spring effect in the old wire would push it back up but just not fast enough to keep it running. I have no idea how many times I put it up and down before I found the problem. Have you tried starting it with it off the center stand? That might tell you if it's the jarring effect or if you are stretching something as you shift the weight from stand to Wheels.

Hi norto, welcome. What year is the bike? Mainstand mounted to the frame? Or to the engine cradle?

pete.v said:

Maybe run a dedicated ground wire to the head via a headsteady mounting bolt to the plus side of the Batt (positive Ground).

Click to expand...

I am going to expound on own reply.

I think Concours is thinking what I am thinking. Maybe not. On the later Commandos, if the bike is on the centerstand, the entire bike is weighted on the iso system and a neutral/ground connection can be made by the resting pressure. When off the stand the power unit is isolated and if a dedicate curcuit/wire is not there, ground can be lost. Even on the earlier Commandos, the power unit is still isolated but the center stand act differently in this regard.

Along with running a wire to the head, connect the neutral wires from the coils and boyer to it if you so desire.

Thank you all for your input.... there is a dedicated ground to the head already so I will try the neutral wires from the coils and boyer!

Just because you have dedicated ground wires to the head does not mean they are functioning as needed. It's an easy check with an extra length of wire and a few alligator clips. Then you will know for sure.