Bullet Mixture Screw Adjustment?

After posting on a motorbike forum and getting no answers, I have decided to post here because people always seem to be able to help me out better at Indiamike.

I'm having trouble adjusting the mixture screw on my Bullet 500.
For quite a while now the petrol has been burning too rich and blackening the spark plug for quite a while now. I've tried adjusting the screw and the best I have been able to get it is where the spark plug gets lightly stained a browny black and the top of the spark plug goes blue. I'm not sure why this is. I don't know how I can get the mixture to burn properly so the spark plug stays clean.

1. Do I turn the screw in for richer and out for leaner?
2. What does the blue top of the spark plug signify?
3. I can't screw it any further out. I'm pretty sure it used to screw further out, but now it's stuffing up.

I'd assume that if the tip of the spark plug is turning blue, then it must be too lean. But so far no one has been able to explain how it all works to me so I still don't know.

Keep in mind that my Bullet has a larger fuel jet than the standard one so it has more petrol delivered which will make the adjustment a little different to a normal Bullet 500.

If someone tells me what the blue means then I can decided whether to screw it in little by little until I get it right or if a mechanic will have to fix the screw up so it has more play.

Thanks for your help

Tighten for a leaner mixture and loosen for a richer one . . . that's the basic, on my standard I let i warm up and then adjust the screw to get a perfect 100 or so bpm thump Then there is the air screw as well, 2 1/2 turns loose after full tightening is what I've heard, but i usually let a mechanic deal with that one until i reach the rare atmosphere of the Himalayas which demand some periodic loosening to allow combustion in the rare air!

Why your plug is turning blue i have no idea . . . maybe it met a tbts and is now pining for a plug to mate with hence blue . . . as in 'I'm blue without you!'

What is going blue? the white ceramic casing?

Then again plugs always get blackened, so long as your bike is running well, I wouldn't worry about a dirty plug, just change it every year or so, and keep a spare handy!

How to get a original spark plug, i hear and have felt Champion and other available off the shelf are imitations as plug in new vehicles runs for years and replacements runs not even full year (which ever source you buy from.)

Mico plugs are what I use, they are easy enough to get, and last for quite some time . . . new vehicles obviously have much less emission than older ones as the engine gets used and podded around things are bound to get greasier quicker!

If your plugs are black, your cylinder is could also leaking oil into the combustion chamber. A problem that cannot be fixed by adjusting the mixture screw.

According the Pete Snidal's Bullet Manual and my testing yesterday, tightening it makes it richer.

He also says that when the spark plug turns a chocolate brown colour, the mixture is optimum.

I haven't managed that no matter which way I have turned the screw.

When I say the top I mean when I'm holding it But I guess when it's in the engine it's the very bottom part that is going blue.

If I follow this then I have to adjust the mixture screw until I get the best engine speed and then lower that until the slowest speed that it is running perfectly.

I'll give that a go today and see what happens.

Now you've got me confused! Will have to go down to my bike and check! Actually you're right, loosening it makes the engine thump slower and tightening it faster! But I'll have a hands on to make sure

The Pilot jet referred to above however seems like the air jet and not the petrol one, then again I'm shooting in the dark I guess!

As far as I know, the screw you're loosening is the idle screw (or stop screw is it is called in the thing I quoted). The mixture (pilot jet) screw is the smaller one to the right.

I had a mess around with it today. Still haven't got it quite right but I'm not in a hurry. My front wheel bearings are totally stuffed so the top speed is limited to around 80km/h and there is hardly any acceleration. Tomorrow I'll try and take it in to get them replaced. I'll also ask them to fix the mixture and watch as they do it and work out the proper way.

Bearing going bad starts giving sounds of all sorts first and then slowly starts to hinder the motion.Lack of acceleration could be weak clutch plate problem.

Actually it has been going bad for quite a while now. Before it only started making noise when I went over 50 or so. Now it keeps getting worse and the front wheel hardly spins freely when off the ground. Because it is slowly down the bike as they are not turning properly, I can't go as fast.