puzzled with some jetting

[QuadJunkies]

I wish I had a lense that would zoom in close enough to show what it is I am trying to describe on the plug,but I dont so Ill try and explain it as best as I can.....

On the upper,outer rim of the plug, is nice and dark,dark brown..The electrode is light brown,the insulator is HALF dark brown to almost black on ONE SIDE,but the other side is light grey to yellow. Needle is dead set in the middle,go one richer and it blubbers BADLY.
162 on the main deep down in the plug is nice and dark, quad is very responsive and crisp on the top end
Basically... How do we get the other side of the insulator to show color?:confused:
Gas mix is 50% VPc12 and 50% 91 octane.

Mix is Belray MC1 synthetic mixed at 44/1.
We have a slightly modified head with a 160 comp. so there is need for some race gas .

Were a little stumped on ths one and really need to get this mini dialed in before we leave the State as we will once again need to rejet accordingly,so having it dialed in at home will make this a little easier.
thanks :)
We are using a borrowed 52mm cylinder until ours is SUPPOSED to show up any day now and had to have a custom head cut for it so my Son could get some seattime just ,he hasnt had any seat time and has a race in less than 2 weeks.

[QuadJunkies]

Anyone ??
I knwo there is several of you out there that have alot of experience :)

We are throwing around the idea of changing fuels this time as well unless advised that C12 mix is the best.

[GPracer2500]

The yellowish coloring is from the lead in the C12. Those deposites are lead salts left over from the lead being oxidized. It's nothing to be concerned about.

As far as the non-uniform coloring of the plug--it's something I've seen but I couldn't say exactly why it happens. I suspect it's related to the particular way in which the a/f mixture tumbles around in the combustion chamber and how that turbulance interacts with the indexing of the plug. In other words, if the plug's side electrode is shrouding the one side of the insulator to the incoming a/f mixture, deposites may not build up on the plug evenly.

Whatever the cause, I wouldn't concern yourself with it. But if the uneveness of the coloring is confusing your plug readings, try indexing the plug so the side electrode doesn't orient perpendicular to a transfer port. Have it facing the exhaust port, perhaps. I don't know if purposefully indexing the plug would get rid of the un-eveness, but it might.

As far as the fuel choice, I'd think most engines would be fine running premium pump at 160psi cranking compression. But that's a dubious generalization that doesn't take into account a lot of important factors (such as air vs. liquid cooling, porting, expansion chamber design, and a bunch of other stuff). I would expect you to find the best performance running straight C12--even if detonation isn't a problem with straight pump. The favorable vaporization characteristics of C12 are especially easy for a two stroke to take advantage of.



I only take plug readings on brand new plugs with hardly any run time on them. I warm up engine on old plug, install a new plug, make a test pass at the appropriate throttle position (I'll pretty much only use plugs for confirming the main), pull the plug and read the mixture ring at the bottom of the insulator. In my experience, too often you can wind up chasing your tale trying to read old plugs for jetting purposes. Used plugs that have been run at all different temps, loads, and throttle positions can't give you specific information.

Bottom line: if the engine runs well because you've experimented with different jetting and found settings that work, don't worry about what the plug looks like. Just $0.02.

[wilkin250r]

I can provide possible explanations, but I don't really have any solutions to them.

2-strokes are funny. They have less moving parts than a 4-stroke, so people think they are "simple". But think about what goes on. The incoming rush of fuel/air needs to push all the exhaust out, even that part that is sitting above the ports.

Envision that for a second. Or imagine something similar. Take two identical glasses of water, and put green food coloring into one of them. Now, pour the clear one into the green one, and try to push out ALL the green water. I bet you push out a lot, but not all, that water still has some green tint to it. This is the same thing that is trying to go on inside the cylinder.

It would be easy to accomplish if you could flood the cylinder with fresh fuel/air slowly, but that's not possible. It would also be easy if you could push 300cc of air into 125cc of space, but that's not possible either. All of this creates very complex airflow patterns inside the cylinder. It took engine designers YEARS to figure this out, largely because computer modeling wasn't possible, and the equations are too complex for a person to calculate by hand (it would literally take years of crunching numbers).

I think this is your problem. The uneven coloring is most likely caused by exhaust still trapped in the cylinder, creating an inconsistent burn pattern. I can imagine the porti layout on a little mini doesn't have quite as much R&D as the larger bikes, and if you have additional modifications to the ports to increase power, that's going to change all that much more.

Whoopee. If that's the problem, how do we solve it? You don't. You live with it. It's still possible to build a powerful engine, it just means you can't really trust the plug for jetting. You'll need some other way to jet it, maybe on a dyno, or even the old butt-o-meter. :ermm:

[QuadJunkies]

That was alot for me to absorb :p lol

I will most def. print this for my Husband

Thank you for taking the time to be so in depth on your post, I appreicate it :)

[ohsobad_chevy]

GP,
What would a guy have to pay you to come to northern Oklahoma and teach me your knowledge. I would love to know half of what you know. :cool:

[atvhonda-rider]

i second what chevy said, but with both of the intellgient answers... im still boggled from reading them both but i liked it... bravo