Spark Plugs - B7ES B8ES or B9ES

OK - which spark plug is the coolest and what sparkplug is the hottest? 7 or 9 ?

I just changed from B8ES to B7ES and noticed a difference.
The difference being a deeper sounding engine that responds more at lower RPM's, but does not run as smooth as the B8ES at 60 MPH.

Is this common?

When I removed the B8ES they were sooty and chared with black carbon deposits, is this an indication of oil getting past the rings or just a sign of old age?

Please comment on what spark plugs you use. Does anyone run the B9ES?

What effects can spark plugs have on the engine?

Thanks

number coresponds to length of insulator smaller number is hotter plug.

Which isnt your problem, it should run on B8's

Try ND W24ES/U. Far superior plug.

Would mostly rely on using factory recommended sparkplug (B8ES) for most of us under normal riding conditions using the full rpm range in a mix of city and highway riding.

Hotter sparkplug (B7ES) runs hotter to help keep plug cleaner and avoid carbon loading under conditions of sustained lower rpm usage such as plonking around town all the time without some regular higher rpm usage (such as an occasional hard acceleration rip through the gears to "blow it out.") The original Z1 Owners Manual said B7ES could be used during the break-in period if B8ES plugs were fouling, but cautioned in bold print to use B8ES after break-in because continued use of B7ES for hard acceleration or high speed could cause engine damage from overheating. The FSM warns further about preignition and burning holes in pistons.

Colder sparkplug (B9ES) runs cooler at sustained hard high rpm usage such as extended high speed operation or road racing to help hold the temp about where it would be with a B8ES under more normal operating conditions. The original Z1 Owners Manual said B9ES could be used for cooler running if ceramic on B8ES plugs was burning white. The FSM warns further about several additional problems caused by carbon build-up on the colder plugs.

Where non-defective properly gapped B8ES plug readings are too dark or too light, it's almost never the plug's fault. But more likely a problem with the ignition, timing, compression, or carbs.

Good Luck!

You didn't say what you are putting the plugs in.
But from what you said you have more then
a spark plug problem.
If your bike calls for B8 putting (colder) B7 will not help.
Putting a B9 (hotter) might but only for awhile.
Your bike has some other issues that should be addressed.
Do compression/leak down test.
How many miles on the motor?

Or it could be something as simple as real dirty air filter.

XENU

Check voltage going to the coil, ohm primary & sec side of coils, ohm resister plug ends, check point gaps & condition

Here you go, all you (never) wanted to know about NGK spark plugs.

www.ngksparkplugs.com/techinfo/spark_plugs/techtips.asp?nav=310

Patton has it exactly right

Great web page
Learn something new ever day.
Thanks

Whats interesting is that the NGK website lists the B7es as the recommended plug for the 1979 650c and my manual says use the 8 for normal use and 7 for city use.

Great info!!

So would the gap on the plug out of the package be fine to use or should I be increasing or decreasing the gap of the plugs?

What is the correct spacing of the B8ES plugs for a KZ650B?

I would run the recommended plug and then do the WiredGeorge coil mod. Good chance this is why your plugs are black and sooty.