a bit lean, now what?

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Apr 2, 2010
starts perfectly with the new plugs and battery
thanks for the input on the ignition probs

now she is running a bit too lean - kinda like pic 22/23

http://www.dansmc.com/spark_plugs/spark ... talog.html

My first thought is to pull the hotter range plugs out that the previous owner had installed and go back to stock N7Y's or the equivalent.
I will do another throttle cut read after that.

Any other wiser types have an opinion? Any help is greatly appreciated.
roqueweiler said:
I will do another throttle cut read after that.

Any other wiser types have an opinion? Any help is greatly appreciated.

I would go with the stock plug.
If after you have done this and a somewhat lean condition is still presant, look for air leaks around the inlet manifolds. To test for this, spray some WD40 around the connection points while the bike is idling. If the idle rises, air is probably getting through. Recondition all mating surfaces, especially the carbs where the ears are usually bent from over tightening. This is assuming you are running 2 amal32 on your 850?

The chop test should indicate the status of you main jet setting. If, after your chop test with the proper plug and have determined that no air is getting in and you still have lean reading, I would then go up on the jet 1 level, for an example if you have 220 go to a 230.
I am also under the impression that both plugs are equal?
Yes I am running 2 Amal carbs.

The plugs are more or less equal; right side somewhat hotter/leaner than left.

I didn't mention that there is NO lean type backfire when suddenly off the throttle. I assume that means that the settings are fairly close?

I am going to put the cooler plugs in and run them then do a throttle chop test and also do the same on an around town sort of putt not the hot highway type run I did last night.

Thanks again - as always, any input is greatly appreciated.
A lot of the pictures you see of plugs were taken on leaded fuel which leaves nice coloured deposits on the plug which are easy to read, unleaded fuel leaves the plug much cleaner.
You shouldn't worry too much about electrode colours but look deep into the plug where the insulator meets the metal.
The higher the carbon ring comes up the insulator the richer the mixture. There should be just a witness ring of carbon at the very bottom, this is a bit difficult to see, an illuminated magnifying glass or otoscope is very useful (cheaper than a pukka plug reader).
Cooler plugs did the trick!!


Now to the charging system - and trying to understand the garbledy-gook language and plainly stupid British names for things in my manuals.

Please see my next post - 1974 Commando not charging
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