one plug looks rich ,one plug looks lean, bike runs fine

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jimbo

jimbo

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One plug looks rich ,one plug looks lean, bike runs fine. starts , idles, revs.The floats, needles, jets are new last year and are OK, mains are not plugged.1975 MKII 850 with stock amals with steel slides, have had no problems with it forever. Changed plugs sameo ,sameo.. Maybe a cylinder/piston is startin' to lose its seal and I'm seein' some burnt oil on one side? Mistaking that for a rich spark plug indication. Doesn't look oily though. :shock:


Its getting my head all scratched up!
 
Maybe try switching spark plugs from one side to the other to see if the condition changes sides, and then try switching coils from one side to the other to see if the rich condition switches sides with the coil swap... A weak spark can cause a rich condition too...

Also maybe one of your needles popped out of the clip or is up one notch accidently...??
 
If you've verified your carb settings (don't assume both carbs should be the same), go through the easy stuff first (valve clearance, switch plugs then switch plug wires) if problem persists and you suspect valve seating, you can pour some fuel into the inlet valve rocker and see if any seeps down into the bore.
 
lrutt said:
how do the pipes look?? same amount of blue basically on both sides?
Click to expand...
old pipes...... look the same over the years to me
 
How drastic is the difference. If they are just a shade or two off, you could put a BP6es in the rich side and a BP8es in the lean side. It's not an uncommon practice. If it's good enough for an old Ferrari, it should be ok for a Norton.
 
jimbo said:
One plug looks rich ,one plug looks lean, bike runs fine. starts , idles, revs.The floats, needles, jets are new last year and are OK, mains are not plugged.1975 MKII 850 with stock amals with steel slides, have had no problems with it forever. Changed plugs sameo ,sameo.. Maybe a cylinder/piston is startin' to lose its seal and I'm seein' some burnt oil on one side? Mistaking that for a rich spark plug indication. Doesn't look oily though. :shock:


Its getting my head all scratched up!
Click to expand...
Something is not balanced. Start with a compression test to assess the mechanicals before you review fuel and electrics as others suggest.
Ta.
 
If it still has dual points ignition, one set may be more advanced or retarded than the other. I would suspect the side with the "lean" plug of having more advance, thus pulling the other cylinder and running slightly hotter.
 
it runs , for the rally it will either blow up or get us around, as I don't have time to make a science project out of it. :shock:
(watch for us along the road)
 
I have previously mentioned here an 850 with exactly same symptoms.
Reasonably freshly rebuilt engine too.

Removing head showed one inlet valve stem seal had 'shrivelled up and fallen off', or maybe viceversa.
Replacing it with new one restored all to good.

Amazing what a trace of burning oil can do to the plug.
It looked for all the world like it was running rich, but changing carb made no difference whatsoever.
 
Rohan said:
I have previously mentioned here an 850 with exactly same symptoms.
Reasonably freshly rebuilt engine too.

Removing head showed one inlet valve stem seal had 'shrivelled up and fallen off', or maybe viceversa.
Replacing it with new one restored all to good.

Amazing what a trace of burning oil can do to the plug.
It looked for all the world like it was running rich, but changing carb made no difference whatsoever.
Click to expand...

good to know ,

makes sense, thanks, I was thinking it might be using some oil , and I will bring some extra.
 
Unless it smokes a lot, it probably won't even use much oil.(hopefully).
It seems to only take a mere trace of oil burning to make the plug look dark.
 
If its running fine, starting easy why worry about it, if the plug colour is not to far from each other all good, but if the plug was very black then i say could be the seal on the guide, but if its not using much oil, it could just be one carbie out just a bit, what side is it running richer the drive side or the timming side, the drive side does more work, but if the bike is running from low revs to high revs without any misfire then it should be alright, its hard to get every thing balanced perfectly.

Ashley
 
Ugh some seasoned Nortoneers might worry its early indication of push rod tunnel leaks beginning to gas jet head grooves that connect to chamber. Do not think of this while riding please.
 
ashman said:
the drive side does more work,,,
Click to expand...

The drive side crankshaft transmits the torque from the timing side cylinder,
so in this respect (and this respect ONLY) that statement is sorta/vaguely/faintly correct.

As far as influencing the spark plugs, or spark plug colors,
there is NO such influence whatsoever.
In a perfect world and perfect universe, each cylinder would be doing perfectly half the work each.
In a perfectly running Commando, they do do half the work each....
As far as can be measured - given they are rather solidly connected together !
 
Rohan said:
ashman said:
the drive side does more work,,,
Click to expand...

The drive side crankshaft transmits the torque from the timing side cylinder,
so in this respect (and this respect ONLY) that statement is sorta/vaguely/faintly correct.

As far as influencing the spark plugs, or spark plug colors,
there is NO such influence whatsoever.
In a perfect world and perfect universe, each cylinder would be doing perfectly half the work each.
In a perfectly running Commando, they do do half the work each....
As far as can be measured - given they are rather solidly connected together !
Click to expand...


In theory and this is only my way of thinking, the drive side of the crank sticks out around 100mm, carries the drive sprocket for the triplex chain that goes to the clutch and has the rota on the outside for the altenator, the timing side sticks out around 70mm, has the cam gear and chain etc, so in theory the drive side be doing more work, if the carbies are adjusted right then they should be the same, but the left carbie could have its needle in a diffrent position than the right, each cylinder runs diffrent to the other side, same as when you pull a head off one side will have brown carbon and the other side will have black carbon but the bike was running great, which side has the darker carbon??? I am just thinking outside the box, maybe thinking to much, time for another beer and think of something else, where will I go for a ride this weekend???

Ashley
 
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