Photo of open plug for explanation

[JCW]

In reviewing recent threads on plug readings, I noted that several of us have had a hard time understanding where the photos were taken. If anyone out there is still wondering, I hope this photo helps. The threads were cut away with a hacksaw.

While you're looking, any comments? This was a WOT check I did yesterday with as many RPMs as I have ever heard a 2 stroke deliver. As I did not have a hill to pull to put a load on the engine, I didn't run it to the completely WOT, but it was about to explode. Also, the bike was warmed up for about 10 minutes and the check was about 15 seconds.

Thanks
JCW

 

[Jaybird]

Mucho fat.
Was that a brand new plug?

 

[skipro3]

Keep working on your jetting until the gray line is about a pencil width thick. As Jaybird is eluding to, that plug looks too dark for a proper WOT chop. Warm the motor up with a used plug and change to a brand new one for the check. Remember to run 30 seconds WOT, 4th or 5th gear on a slight uphill and cut the throttle, pull the clutch and hit the kill button all at the same time. Even a slight delay on any of these will cause the plug to read incorrect. If you don't have a hill to put a load on the engine, try riding the rear brake pedel for resistance. WOT means WOT and backing off won't give a correct read. I've not heard of a stock two stroke that could over rev to the point of exploding and I wouldn't worry about it. If you just can't bear to do it to your own bike, have a friend do it for you. Most friends are more than happy for the opportunity to damage someone else's bike. (That last part is a joke,, your bike can handle a WOT for 30 seconds)

 

[JCW]

Thanks,

I thought it was a still rich, although it's much better than stock. I took it out for some technical woods riding and open road riding and it is still rich, but runs good. I will put the 152 main back in and re-test it. This was a 155.

I also put a 14 tooth countersprocket on the front and it runs like a crotch rocket. It used to rev and really pull strong, but it never built up a lot of speed. With the 14 sprocket I still have plenty of power to pull a hill and now it rocks you back on the seat and pulls hard and steady like a YZ400F I used to ride. Now I have my mid and top end speed back!

I'll have it dialed in shortly-
JCW

 

[JCW]

Oh yeah, regarding blowing up the engine from high RPMs, it can happen. I've seen it happen a couple of times and unfortunately it happened to me. In my case, a wiesco "hot rod" (in my respectful opinion, aka "piece of .....!") exploded and destroyed a KX engine. I am aware of another wiesco hot rod explosion. Remember, friends don't let friends buy wiesco.

 

[skipro3]

Hi JCW,
I'm sorry to hear of your experiance with blown 2 strokes from over rev. Yours is the first I've heard of a stock bike doing so. I have seen oil failures that have cause seizeure but that is different. I thought the CDI unit or the coil would limit the revs enough to prevent the bike from damage. I am interested in your experiance with wiesco pistons. Many KDX220 owners have changed their stock piston to the wiesco because of skirt breakage on the stock piston under normal operating conditions. I am in that crowd who swapped to a wiesco. Please fill me in on what you know about the problems with wiesco. Thanks!

 

[JCW]

While I will never personally buy anything Wiesco makes (and many of the mechanics here won't either), I think their pistons are probably OK, although I like Vertex and ProX much better. The hot rods (in my opinion) are junk! There are three people in this area that had engines "explode" (and I do mean explode) at high RPMs with a Wiesco hod rod. The rods break in half and take out the entire motor. One person who saw mine asked if lightning struck it.

My stock 03 KDX doesn't have one, but after that experience I am a little apprehensive on WOT as you might understand.

Thanks,
JCW

 

[Rich Rohrich]

Originally posted by JCW
As I did not have a hill to pull to put a load on the engine, I didn't run it to the completely WOT, but it was about to explode.

Be careful about getting too aggressive leaning it out based on this plug reading. Don't forget fuel demand is a function of engine load, so no load plug chops will always read too rich. Under a load you'd see a much different , and IMO much more representive view of what's going on. Plug temps are also much lower when there is no load which is another thing to keep firmly in mind. You can easily get a false sense of security with a no load plug reading.

 

[JCW]

Rich,

Thanks for responding. Any suggestions if I don't have any hills near my home to create a load? I don't know how to create a load on the engine for an extended period like 20-30 seconds. The bike has so much power that after a few seconds of WOT, it's overpowered the load and it's free reving. That's why I did what I did.

Rather than switch to a 152, I kept the main jet at 155 and moved the needle up to one clip from the top (up one clip) and it still runs very well. I don't see much smoke coming out of the bike (nothing like it smoked when it was totally stock).

Thanks for your help. I'm a "newby" to doing my own jetting, although this is really fun and Dave's site has really helped me understand how the carb and proper jetting works. Canyncarvr and Canadian Dave have been helping a lot and I really appreciate you guys comments and suggestions.
I want to get it right and hopefully help a few others who may be new to jetting while I am working mine out.

JCW

 

[Rich Rohrich]

Sand and mud can provide additional load if needed. You could even tow another bike if need be. :)


The important point is to try and match the load you jet with to the maximum load you'll see when riding. If you ride somewhere new that will load the engine much harder, just keep in mind your engine will require additional fuel across the fuel curve.

 

[JCW]

I see now. I'll drag a 150 lb anvil behind the bike. That should do it! I can't believe I didn't think of it earlier.

Regarding matching the jetting to my riding style, I don't think I'll ever run the bike any harder than I did for this test.

Thanks
JCW

 

[wibby]

Oh yeah, that oughta do it :eek:

 

[jirvine]

Do you always use a new plug on each reading? Starting to get a lot of used one time plugs!

 

[JCW]

I'm with you on the one time plugs. Hopefully, once we get it dialed in, we won't need to keep destroying plugs. If you can avoid cutting them open and look down inside the plug, obviously you could still use it. I've tried this with a magnifying glass and a flashlight and I can't tell how big the ring is, etc.

This is my first attempt at jetting myself and I think it will take about 5-6 plugs, which is a relatively cheap experience, especially since we are fortunate enough to get the training free on this site. Besides it's fun and it will pay off when seasons change or we go to different altitudes, etc.

JCW