73' Norton Exhaust Note

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Hey guys -some of you may have seen my other thread but I just bought this 73' Commando 850 - it seemed like it was running a little lean to me (a lot of throttle hang and some backfiring) and was idling at 1,300 hot so I took that down a bit to more like 1,100. The right pipe is making what (to me - an uneducated Norton fellow) an odd sound out of the left cylinder. I put a link to the video below. You can really hear it around 10 seconds in on. The other cylinder just pops right along fine. Any thoughts if that's out of the ordinary - sounds like a bit of a misfire to me. Bike runs great throughout the power band - like I said was a little lean at idle I believe - it was set up in October which is a good bit warmer here in Phoenix is my guess.

 
Based on the video, I think most likely it's just needing idle air/fuel adjustment or idle slide stop adjustment. If that's not the issue, could also be a slight vacuum leak on one carb or some restriction in the idle circuit/some cleaning necessary.

Does turning the idle air screws in/out affect the idle?
 
Based on the video, I think most likely it's just needing idle air/fuel adjustment or idle slide stop adjustment. If that's not the issue, could also be a slight vacuum leak on one carb or some restriction in the idle circuit/some cleaning necessary.

Does turning the idle air screws in/out affect the idle?

Thank you for your reply. It does effect the idle but the sound doesn't go away.
 
It had the carb cleaned in October but it has sat since then so perhaps a clog in the idle circuit. I have dealt with the Amals before. Just a weird noise but maybe I have "new toy paranoia" too :)
 
Sorry if I keep banging on about it, go and buy yourself a second hand Colourtune of the correct type sparks plug, use only at night when the moon is up, or a very dark garage. You will, if you learn to read it diagnosis whether it's a fuel or ignition related fault. Lots of people have said they are u/less - but they tried to use it in bright sun light.
 
There's a few different tools to help get slides the same height at idle. My favorite came from a Solex manual for the dual sidedrafts on a bmw. Use a short length of hose around 1/2". One end at the carb inlet, one end at your ear. It makes a swish swish sound. A more closed slide and the sound goes quiet. Very easy and very accurate. Then do a cables tight test at half throttle or so with motor off and drill shank under the slides
 
I notice in your second video that the choke lever isn't in the fully off (tight wire) position. Is that intentional?
 
Sorry if I keep banging on about it, go and buy yourself a second hand Colourtune of the correct type sparks plug, use only at night when the moon is up, or a very dark garage. You will, if you learn to read it diagnosis whether it's a fuel or ignition related fault. Lots of people have said they are u/less - but they tried to use it in bright sun light.

I have one and will check it out.
 
I notice in your second video that the choke lever isn't in the fully off (tight wire) position. Is that intentional?

Well, that's another issue - I am going to speak with the gentleman that did the work but it dies if you swing the choke all the way open. My guess is there is some sort of leak.
 
You really need to compare the two...Very hard to diagnose without hearing both at the same time.
However ......It sounds similar to the side that is being "pulled" by the (other) strong side.
I would reduce the idle speed of the (strong) other side(a tiny bit), then tweek the mixture on the recorded weak side.
All this is relatively unimportant since you are hopefully at cruising throttle most of the time. At cruise the cable synchronization is all important and the idle sync is virtually irrelevant...
Non identical side to side timing can complicate matters.
1 all mechanical adjustments..valve clearance
2 ignition setting
LAST
3 carb adjustments
 
Good audio. That sound is what I hear when there is a slight misfire.
Make the misfire go away, the sound will too.
 
Hey guys -some of you may have seen my other thread but I just bought this 73' Commando 850 - it seemed like it was running a little lean to me (a lot of throttle hang and some backfiring) and was idling at 1,300 hot so I took that down a bit to more like 1,100.

“Throttle hang”?

High idle can sometimes be caused by a hanging Ignition Automatic Advance Unit (AAU). If you are still using points ignition, this can be an issue. If you are using electronic ignition, please disregard this.
 
FWIW, One method I sometimes use to adjust idle synchronization AFTER ensuring throttle cables are adjusted to ensure your slides are lifting in sync..

With the engine warmed up:

Pull one spark plug then reconnect it and lay it on the cylinder head. Start the bike and set the idle on the running cylinder to the lowest RPM it will smoothly idle - probably around 500-600, adjusting the idle air screw to obtain the best running. Now remove that plug/reconnect/lay on cylinder and install the other plug. Do the same process and set the idle stop screw at the same RPM, again, adjusting the air screw for the best running.

Put that spark plug back in/connect it and start bike. It will now be running smoothly at around 1100 RPM. If the idle is too fast, Very carefully back the idle stop screws out on each carb an equal amount by maybe 1/16 turn for each at a time until you get the idle speed you want.
 
I was able to get the misfire to go away by enrichening the left carb - but I am slightly inside one turn towards fully closed on the air adjustment screw and the bike will stall if I go full choke off - so to me it is still way too lean - its cold here so the air density is up, but still. I am wondering if there is an issue with the fuel delivery system? Dumb question but do I need to turn on both petcocks (reserve side and left side) to run the bike? The manual says only to turn on the left side but if I dont turn on both sides, the right carb will not tickle. Could that be part of the issue? Also I can see an air bubble going into the right side carb in the fuel line that doesn't go away if I turn the right petcock either way. Any ideas there?
 
This happens to me if the fuel line or screen is plugged somewhere where it connects to the bottom of the float bowls. The reserve tap is hardly ever opened so sediment can't get flushed through that area. Disconnect the fuel line completely and see if you can blow through all orifices. Also check both screens. My yellow tyvek fuel lines from ebay dissolved and produced water and gray goop which clogged it all up.
 
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