Stalling problem

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Feb 21, 2005
Any hints as to why my 74 850 Commando stalls without warning at idle.I have in place boyer ignition, was thinking the next step may be to sleeve the carbs. What do you think

You have opened a HUGE can of worms here ~

"We " need to know .. how many miles on your bike..or more importantly on your carbs.

Maybe worth having a look over my feature on the opening page which Jerry posted.. regarding carbys.. ( I could add a lot more to that since writng that feature too )

If your jets are worn.. if in fact your slides and bodies are worn.. could be loose wires in the pick up of your Boyer. ( a common problem~)

What are your plug leads like? I fitted copper ones ~ with advise here on Jerry's site... OK to fit on Boyer Mk I .. much better!

I found one of the O rings between the body of the carb and the manifold was missing and the mount nut worked loose enough to cause idle and starting problems..

The list goes on and on.. for such a simple system the whole setup is extremely fickle~

You really need to start at the bottom and work through.

For example ~ needle jets and carb fittings are not expensive.. I had huge results from replacing the small carby parts as suggested in the feature.

My A65L , worked reasonably/ quite well considering the slides were worn and the bloke I bought them from had replaced them for the thought he felt that they were worn out! That Included idling..

The Amals I feel have never been famous for their consistency I reckon.. even now I find the idle wanders around some what ..

My Trident T160, Amal slides could be actually be heard.. felt rattling and it was fine.. (Of course there is point where they have to be ditched ! )
Think that if he says "without warning", that means the machine is idleing along fine and drops dead without beforehand missing a beat. Only a spark problem can cause that. Or a Boyer that is running just at the limit of it's ability to stay alive because the battery is totally dead...mine won't start if the battery is too dead, and I mean with the kickstart, I have no starter motor.
If on the other hand, if the thing starts to slowly lose rpms, starts coughing and then gives up the ghost...that would perhaps point towards the carbs or a plugged fuel filter, or if the tank is full, full, maybe a blocked gas cap vent(vacumn in the tank).
In my limited experience, those carbs will keep the motor running even if they are in very bad tune or condition, last summer, mine started to run a bit rough in France on holiday, and 4 days and 500 miles later, I got home and finally bothered to look at the bike. Turned out one main jet, complete with the alloy holder, had fallen into the carb bowl. The bike still started up, ran pretty ok, you just needed to give more gas to get away from a the motor can't be too fussy what it gets from the carbs...not fussy enough to cause the bike to die without warning.

He has to explain exactly what the machine is doing before anyone can send him in the correct direction.......I bet the carbs are still good enough to at least keep it running and the electrics have a loose connection somewhere...Peace!
Easy way to check

Have you synced the carbs lately? No, that won't cure this problem but it will help to isolate things. Remember how to sync the carbs, how you keep it running on one cylinder while you adjust the air screw (with the idle turned up a little to keep her going)? Well, do that and see which cylinder has the problem or if it happens on both. You might find that one cylinder is cutting out and taking the other with it. Yo ho ho we'll all go down together type stuff, it is British afterall.
Anyhow, try that and make sure your idle speed is set per the book to begin with! Hmmmm, well maybe that carb syncing might just cure things afterall....
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