Spark plug

Ok, I'd like some input on exactly how to read a plug. The base of the insulator, that little ring determines your main jet? My plug goes like this. The electrode is a black color, the insulator is white and on anther side of the plug, it is a tan color. The little ring around the insulator is a dark brown with some black spots (maybe a tad rich?) I have heard so many things from people know I have gotten confused. Does the plug really tell you anything? My bike is really running strong and only requires me to adjust my air mixture screw most of the time to achieve max performance. Thanks

How long was the plug in the bike. Anything more than an hour, and any reading you get from it is meaningless.

If the plug was less than an hour, it sounds like your jetting is close (maybe a hair rich - which is ok), the flow of your transfer ports is a bit unbalanced (normal in a stock cylinder), and your plugs head range is one too cold.

But if the plug was in longer than an hour, forget everything I just said.

-Steve

The plug was in the bike for about 1-2 hour ride. The idiots who installed my tire pinched the tube and it blew out. It runs really good but I dont understand after hours of riding usually my plug turns black. Could my Klotz oil be it? Spectero blackened all my plugs but maybe klotz is just clean?

Steve, I disagree on the one-hour thing with plugs. The plug I have in my bike has over 12-15 hours on it, and it changes colour constantly. If I go for a very very hard ride it goes back to the normal light tan colour on the insulator, and the ring around the base goes back to a tan colour, instead of a dark brown.

Derek wrote:

Steve, I disagree on the one-hour thing with plugs. The plug I have in my bike has over 12-15 hours on it, and it changes colour constantly. If I go for a very very hard ride it goes back to the normal light tan colour on the insulator, and the ring around the base goes back to a tan colour, instead of a dark brown.

Was it you that said you would never disagree with Steve in that other post, or was it some one else??

twosmoker wrote:

The plug was in the bike for about 1-2 hour ride.

Then the plug reading is viable. Any longer than that, and I would start with a fresh plug to take any readings.

The idiots who installed my tire pinched the tube and it blew out.

Time to find some new idiots...LOL

It runs really good but I dont understand after hours of riding usually my plug turns black.

The longer a plug is in the more buildpu os on the end. The end will indicate how hot the combustion chamber is getting. Too dark and the combustion chamber temps aren't high enough to burn off the residual oil. Too light, and it's too hot. If you constantly have too dark a plug, but you know your jetting is spot on, then go up one heat range on the plug for your riding style. An expert on the same bike would probably be ok, and may even need richer jetting.

Could my Klotz oil be it?

No.

Spectero blackened all my plugs but maybe klotz is just clean?

Klotz will run much cleaner than Spectro. However, that is not the issue here. What you are seeing is the temperature of the combustion chamber. Nothing more, nothing less.

-Steve

Derek wrote:

Steve, I disagree on the one-hour thing with plugs.

That's cool. Open discussion of topics like this help lots of people learn.

The plug I have in my bike has over 12-15 hours on it, and it changes colour constantly. If I go for a very very hard ride it goes back to the normal light tan colour on the insulator, and the ring around the base goes back to a tan colour, instead of a dark brown.

Ok, this is telling me a couple of things. (spark plugs are amazing things... even though they don't talk, they can tell you lots of information about how your engine is running)

1) Your jetting is VERY close.

2) You should really be rejetting to how you intend to ride.

3) Your engine is VERY sensitive to jetting changes.

Here's why...
When you go for an easy ride the plug tip darkens because the combustion chamber is not getting hot enough to burn off all the residual oil. When you go for a hard ride the combustion chamber is getting too hot. When you ride it like you normally do, the bike probably runs really good.

This isn't a bad thing. It's actually a good thing, and also a good thing that you take the time to look. For an engine to work optimally, the combustion chamber has to get hot enough to burn off most of the deposits that would form on the cylinder head and piston. If it does not, carbon will form, and plugs will foul. If the cylinder gets too hot, then it will burn off all the deposits, and probably vaproize some of the oil that is on the cylinder wall (that's REAL bad).

What tells me the above things is that the plug actually changes colors based on how you ride it. If the bike was not sensitive to jetting changes then the plug color would be more consistant. If your jetting was not very close to begin with, how hard you rode it wouldn't make much difference. #2 above was my personal interjection.. not really anything gleaned from the plug color.. lol

Now, here's the rub. It was probably not changing color as much before you started running two base gaskets. That's because you have changed the compression ratio, squish clearance, squish velovity, port timing, and combustion chamber temperature. Because of the these things, the engine has to run hotter to burn off all the oil. And you changed what I did inside your engine. Yes, then engine will run on pump fuel like that, but it will not run as well, or as consistantly.

I hope this helps clear it up.
-Steve

moto814 wrote:

Time to find some new idiots...LOL

[

Yeah this idiot hehe. I am running a BR8EG, could my jetting be lean? I was riding it somewhat hard but not really.

But how could my jetting be lean? It runs so crisp it has no blips or bogs or anything throughout the rpm range. I hit it and it goes. If anything its rich, but remember half of its white the other half is tan.

Thanks actually. Thats actually how it's been working. It is VERY VERY sensitive to jetting changes, I'm talking up to 1/8th turn of the Air screw here. I was out at a local track on saturday, and I literally had to get the screw within 1/8th of a turn to run well. Changed it a few times as the weather changed over the day.

Since I am keeping my 125 for another season, I will be running Av gas as soon as my ring and base gasket come in from my dealer. The bike runs good now, But I liked it 10X more when it was running on 100LL.

Kxracer, I don't disagree on Steve with most things haha. With the plug thing, I didn't know what was happening since it was changing colour depending on how I ride, like he said.

So your gonna remove that 2nd base gasket? Didnt you get the head shaved or something? Why did you add the 2nd gasket then? Did you not have the gas at the time or something?

Twosmoker, I got portwork done by Steve, and I got the head rechambered and milled for more compression. I did not have the money to run the Av-gas when I got my engine back together after my crank bearings blew, so I have been running two base gaskets.

Oh ok I figured it was something to do with gas.

Steve I still dont get why my insulator is so white? Every other time it has been black with similar jetting. The only thing different now is the oil. I ran Spectro earlier now Klotz

You said the insulator was white on one side and tan on the other. That indicates (the tan color) that the jetting is close. The fact that it is colored differently on opposite sides indicates an mismatch of flow from the transfer ports.

If the Spectro was coloring plugs darker, the plugs were either in too long, or your jetting was richer at the time, or you were not riding the bike as hard. All of those things will cause the combustion chamber temperatures to fall and cause plugs to be colored darker.

Want a quick, cheap, simple performance boost on your CR250? Change the plug to a BPR8EG or BPR8EV. The "P" stands for projected tip, and sticks slightly farther into the combustion chamber. That in itself doesn't do anything for the power, but because it takes up more room inthe combustion chamber, it increases your compression slightly. You will get slightly better pickup and pull in the bottom and middle, and still be able to run pump fuel.

-Steve