Is it unusual to have to raise the main jet higher than a 155? I did a plug chop last week and the plug looked cleaner than when I put it in. Im running 42/155 w/ stock needle in the 2nd to top position. I also live in dallas tx and it was about 75 degrees that day. I was really surprised of my lean findings.
155 and lean
- Thread starter cb-radio
- Start date
- Jan 8, 2000
- 3,331
- 1
The only way to find out is to go to the next size larger (158 I believe) and see how it runs with a richer needle. If throttle response improves, and the plug looks nice and tan, you were too lean.
John Harris
Member
- Apr 15, 2002
- 552
- 0
I too am surprised at your lean findings, but you did not tell us how your KDX was modified. This will affect how rich or lean the main needs to be. Do what the captain says and try it larger. Do not ruin your engine running lean! Cheers John
G. Gearloose
Pigment of ur imagination
- Jul 24, 2000
- 709
- 0
You may not be too lean. The plug should self-clean. You must cut the threads off the plug and check the width of the black ring on the insulator and jet accordingly to truely approach maximized performance.
Tan, after a plug chop, is not too lean. Its good enough for some people, and too rich for others.
If you want to ride max performance, then adjustment to weather will be typical.
Naturally, any grey on the cathode is very bad and means you are a couple steps too lean and will grenade it.
Tan, after a plug chop, is not too lean. Its good enough for some people, and too rich for others.
If you want to ride max performance, then adjustment to weather will be typical.
Naturally, any grey on the cathode is very bad and means you are a couple steps too lean and will grenade it.
- Thread starter
- #5
It is a 96 200 and has an fmf fatty pipe and fmf spark arrestor,torque ring, airbox mod, ported intake and exhaust ports, stock reeds, 40:1 silkolene pre mix...nothing out of the ordinary. The motor also has a brand new top and bottom end. I guess my best option is to just try the larger jet. the inside plug insulator was a white as can be no tan at all. Can reed quality effect air/fuel ratio?
G.Gearloose is right! You've got to cut the threads off to see the ring around the base of the insulator. The tip of the plug won't tell anything about your main after a plug chop on a brand new plug (Well, unless it's grenaded). Here's what I did: Warmed the bike up, put in a brand new plug and then did a drag strip pass to 5th and held it there for about 15sec going up a slight hill on my street. After the plug chop, the plug looked like brand new on the tip. I used a lathe to cut the threads off and tada! There was grey/black ring about 2mm around the insulator. A little bit rich, but I'd rather be safe than sorry.That's the area of the plug you need to look at when checking your main. I've got an 01 KDX 200 with a 155 main and 45 pilot and clip at 2nd position from the top.
The key here is when you wrote that your engine had been ported!! That makes a big difference in how rich you should go on your main jet. In many cases you'll need to have a bigger main to be jetted properly. Also, the aftermarket reeds/reed blocks will need to run smaller mains than stock reeds (possibly 1 step).
