[JoeSchmofo]

Thanks Steve, I'm going to pull the plug out tomorrow morning to see what that'll tell me....

These short days mean I have no time for tinkering.

[JoeSchmofo]

Here's my spark plug. It's obviously running too rich and will be going back to the dealer.

[crock]

After years of running dyno tests and doing plug chops, i am not on board with the idea that reading the plugs gives you any indication of the air/fuel ratio. You can have cars/bikes running A/F of 12:1 with white plugs and 15:1 with black sooty plugs. My conclusion was that the plug reacts to temperature more than anything else.

[gremlin]

........ My conclusion was that the plug reacts to temperature more than anything else.

I'm right there with ya!

[gashousegorilla]

Here's my spark plug. It's obviously running too rich and will be going back to the dealer.

   That plug looks like the bike was idling for a while and or slow speed riding.  And the motor didn't get very hot for very long.

[Arizoni]

That spark plug looks like it's been run on an engine with a plugged air filter.

It's really carboned up so badly I'm surprised the engine was running.

If I was wondering why, I'd check to see if the paper air filter wasn't covered with oil before I did anything else.

[JoeSchmofo]

   That plug looks like the bike was idling for a while and or slow speed riding.  And the motor didn't get very hot for very long.

....definately not the case, beleive me.

I'll check the air filter tomorrow.

[SteveThackery]

My conclusion was that the plug reacts to temperature more than anything else.

Of course!  You are spot on - that is what the colour of the plug tells you.  A rich mixture makes the plug run too cold (blackish), and weak mixture makes it run too hot (whiteish).  But you can also make the plug black or white just by installing the wrong temperature-range plug.  An excessively cold-running plug (short heat path) will run black, even when the mixture is spot on.  Ditto with a plug that has an excessively long heat path - it gets too hot and goes white.

That is why it is essential that the correct heat-range plug is fitted before trying to interpret the colour.  If it is the correct plug for the engine, then it's a reasonable indication.  But as has also been said, lots of slow running, or cold running, also makes the plug run colder than normal, so it picks up a black colouration even when there is nothing wrong with the mixture.

[JoeSchmofo]

Ok, so I live in wet cold London, what temp plug do you think I should use. I took the bike back to the dealers and they couldn't find anything wrong. They said that my pattern of use. (a daily 5 mile commute) might not be helping as the bike doesn't have enough time to get warm.

Any thoughts?

[johno]

I'm in Uk as well, go for the NGK BPR6Es plug (not the 8 as some sites recommend) which can be found in most auto factors so is not difficult to find. if you still have fouling problems drop down to a BPR5Es normally used for short journeys as the tip of the plug retains the heat.

NGK plugs (although some hate them!) can help smooth the idle speed as well as improve on combustion from the OEM plug in an RE efi engine.

[JoeSchmofo]

Thanks Johno. I'll try dropping down to a six.

[Mr.Mazza]

Ok, so I live in wet cold London, what temp plug do you think I should use. I took the bike back to the dealers and they couldn't find anything wrong. They said that my pattern of use. (a daily 5 mile commute) might not be helping as the bike doesn't have enough time to get warm.

Any thoughts?

5 miles isnt really enough to really get the bike warmed up, go find some fun roads and get it open!

[crock]

Put 600 miles on it today. Idle speed has been stable and within spec since i adjusted it around 151 miles.

[Arizoni]

For what it's worth, with NGK and Denso, the larger the number, the colder the spark plugs heat range is.

With Bosch and Champion, the larger the number, the hotter the spark plug heat range is.

For you newbies, the heat range is a measurement based on the temperature the tip of the center electrode (where the spark occurs).
The center electrode insulator tip needs to be hot enough to burn off any carbon deposits that form on it but cool enough so it does not ignite the air/fuel charge while it is being compressed.

The colder the spark plug's heat range is, the less likely it is to cause pre-ignition or pinging but the cold spark plug is more likely to build up carbon deposits which will short it out causing it to quit sparking.

The hotter the spark plug's heat range is, the less likely it is to build up carbon deposits on the center insulator tip but the more likely it is to cause pre-ignition.

Ideally, the spark plug will be somewhere in the middle, burning off the carbon but not lighting the fuel/air charge until the spark occurs.