White Spark Plugs

My '75 Commando seems to have begun to run lean. It runs OK but has developed a case of plug insulators going white.

Last year 'til the time I put it away the plugs showed the proper tan colour.

This year I inserted a set of NGK Iridium plugs. These plugs ran OK but showed white insulator (very lean). Undeterred, I shifted the needles to the lowest notch, from second notch, to ritchen the mix. Also inserted a new set Champion N7Y.

After a 30 mile run, same condition occurred: same white colour insulators (lean). What's more the bike ran fine the first 20 miles but began to run rough in the last 10.

Should I up-size the main jet and revert to second notch on the needle?

Thanks!
Stephen

Interesting. Plug heat range drifts to mind to consider also. Peer in at piston tops to get a sense of their coating and also a wipe of the finger in exhaust, which classically should be light grey dry dust. Suspect fuel flow through float needle seat past needle into bowl too. Can't hardly hurt nothing but power going too rich so let us know, what might of changed besides plugs.

I'm not at all sure the classic plug reading wisdom works these days given new fuel compositions. But I'm willing to be re-educated...

Do not look to the porcelain for jetting. Look at the base ring of the plug for jetting indicators. The ground strap which is welded to it will show your heat range.

Nw age lean burn gasoline should still give basic light tan near end of insulator when mixture is pretty good - as Stephan reported prior. Also should see some black dry soot on rim of threads but not carbon crust. Don't know how heat range shows up on electrode hook, just that spot on spark timing is supposed to show thermal stain just below the bend. Might try a new set of prior plugs to see if they show the same tan as prior to isolate that factor to tease with us further.

Looking into the cylinder at piston tops I note they are both black. The right one has a fine crusty black carbon I could sample with a driver blade.
SC

Air leak at the manifold? for suddern weakness...but black pistons :?: Pass on that one,

chasesa said:

Looking into the cylinder at piston tops I note they are both black. The right one has a fine crusty black carbon I could sample with a driver blade.
SC

Click to expand...

Put 100 miles on those plugs and recheck. I will bet you will see a nice gold color.

This first one is a somewhat new plug after jetting a new carb.
The second pic is the same plug after a hundred mile run in the country.
I see these pretty much ideal.
The second pic also shows a slight witness mark just to the bend of the ground strap. Perfect heat range.

Look for the cener electrode rounding its edges at the end . Signifies a bit much ignition ( advance ) OR to HOT a plug .

Intresting the Champions in the race T100 R lasted a lap & a half . Fairly Common . N57Rs fitted . No Problem .

IF you are out in the wildes and have the throttle ' advanced ' somewhat more than occasionally , a step harder plug might be the go .

HOWEVER , richening the mains aint gonna harm , as a test .
ALTITUDE & Jetting are interrelated , as is barometric pressure .

Richness is the lumpy bit , leaness a intermittant miss .IF theres a ' bit of a cut ' / hesitation occasionally , Jet Up ( bigger ) .

If its got the old Mk 1s , wear can also affect things , Moreair getting around the sides of the slides , and generally stuffing up the equation .

Could be a change in gas formular too . :?

With the Triumphs , the N3 ( T120 ) , or N4 / N5 is reccomended . the N3 will go sooty if trundling around in the cold & wet . But a N5 is to ' soft ' ( HOT ) for
getting to enthusiastic . Differant plugs for in town / traffic , and touring in the death valley , wouldnt be a bad idea . Getta the ' plug read ' book .

Blistering & or scale on the Cr insulator is a no no . Touring at a fair crack of the whip , the plugs and entire insides of the Commando exhaust system were
bright white . No electrode erosion ( rounding ) fair sizzle from the engine , pulling in . About max. lean condition . 70 mpg. Mk 2 Amals . 270 mains. 31 deg
ignition . :shock: