Just posting to add general experience of the gz.
 

Welp 4 hours yesterday and another 2 to three today.
Yesterday
Set tire air pressure dead on.
Clean and lube the chain.
Change the oil and filter.
Lubricate the cables.
lubricate, clean and adjust rear brake.
Polish the chrome.

Today
Replaced front brake pads.
Adjust valve lash.
Fix oil leak.
Clean engine.
Replace spark plug with one of those 'E3's'
Polish some more chrome.

Notes:
You can run A F'N ton of Slime in a motorycle tire and not have issues.
Slime is amazing at fixing bad leaks though it sometimes requires a little finesse.
Still running Rotelle oil.
My bike seems very happy with a slight overfill of oil.
Front brake pads wear out fast.
Intake valves were dead on but exhausts had ate up nearly all their clearance.
Keep your engine clean to keep cool.
I know some say high octane is a waste. My owners manual says 91 or better.
In Texas you have 87, 89 and 93. At least at my station. So 93.
And when I get really hot I get a tiny bit of predetonation so... 93 octane.
It's more resistant to predetonation due to hot spots caused by carbon build up. That and it burns slightly slower.
I'll let you know if I notice a difference with the E3 plug.
I did notice a difference in my old hot rods when I went to high end plugs
so I'm hoping I get that here.
My old NGK plug came out reading slightly hot but in the ok range.
A white-ish coating.

50 miles down the road. E3 spark plug did help a little. I'm running a E3.36 in this GZ.
I'll further update you down the road a ways.

http://www.gz250bike.com/forum/attac...1&d=1472512907

Old plain jane plug. Looks a bit hot and lean but ok.
Opinions?

Oh! And if you change to E3 you should know it takes a different size socket so your original bike tool kit cannot pull the spark plug any more.

Your plug looks a little greyish. I think you are right, you are running a little lean. I had the same issue and adjusted the carb. I don't have to touch the choke at all now to start it up cold. Seems to run OK going down the highway as well and doesn't seem to run as hot as it did before.

Welp. I got a week of commuting on this plug now. It is making a tiny bit more power. No doubt. And the plug was only 6 bux or so... money well spent?
I'll pull the E3 in a month or so and post a pic. See how it's burning.

I bought my gz for commuting too. How are they at highway speed?

The GZ can be a pretty good commuter as long as you stay off of freeways. Secondary highways is where the bike shines. 60-65 mph is about tops with a bit left over. Competing on a freeway will run the bike too hard and issues will arise. The GZ is what it is and it has it's limits.

I ran mine for 42000 Km at speeds of average of 100 Km/60 MPH.....As WW stated this bike is great as long as you don't push past it's limits.