Spark plugs colour

[Doctor T]

To start the bike is a 2007 RT with 42000 miles on the clock with full BMW service history. plus a full service from me.

I returned earlier this week from just over a 2000 mile trip around France. Thought i would give it a go over to check for loose bolts etc. Checking the spark plugs which are NGK Iridum DCR8 EIX. The top 2 are a light brown/grey colour but the lower 2 are a lot darker in colour. I know the bottom 2 are for tic over, low revs and then once the revs creep up the top 2 two come into play. I get 58 to 60  imperial miles to the gallon. The bike runs great, no smoke or rattles but am just worried about the bottom 2 plug being a darker colour. Is this usual?.

Ive ballanced the throttle's and the valves are within tolarance before i left for the trip . 

[dirtrider]

1 hour ago, Doctor T said:

To start the bike is a 2007 RT with 42000 miles on the clock with full BMW service history. plus a full service from me.

I returned earlier this week from just over a 2000 mile trip around France. Thought i would give it a go over to check for loose bolts etc. Checking the spark plugs which are NGK Iridum DCR8 EIX. The top 2 are a light brown/grey colour but the lower 2 are a lot darker in colour. I know the bottom 2 are for tic over, low revs and then once the revs creep up the top 2 two come into play. I get 58 to 60  imperial miles to the gallon. The bike runs great, no smoke or rattles but am just worried about the bottom 2 plug being a darker colour. Is this usual?.

Ive ballanced the throttle's and the valves are within tolarance before i left for the trip . 

Afternoon  Doctor T

 

Perfectly normal, all the combustion & oil residue tend to migrate to the bottom of the cylinder so the bottom plugs will typically show much darker.

 

If you really want to see what the lowers are doing just install new lower plugs, then take the motorcycle for a nice long high speed ride. Then allow engine to cool, then remove & look at plugs (the lowers  should look pretty close to the top plugs)  

 

Then do a couple overnight parks after riding with a few cold starts then check the lowers again (they will probably look just like yours do now).