Bike runs bad after removing airbox lid

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Hawk5443

Member

Apr 15, 2008

21

0

• Aug 15, 2008

• #1

I have read on this site that one of the most frequent and inexpensive mods on the KDX is to remove the airbox lid. My '03 KDX 220 was running a little rich and putting out a bit too much smoke and spooge, so I took off the airbox lid. When I did, the bike ran rough and seemed to smoke more. I had stock jetting at the time. I had to put the lid back on for it to run right. I have since raised the clip on the needle valve to the top position and changed out the main to a 40. I have not messed with the pilot jet. I have not run the bike since making these mods. Am I going the right direction here?

Thanks.

 

whenfoxforks-ruled

Old MX Racer

~SPONSOR~

Oct 19, 2006

8,129

2

Merrillville,Indiana

• Aug 15, 2008

• #2

Is your bike in top mechanical shape? Top and bottom end, reeds, plug, air filter and silencer? I would get the jetting spot on first. Start with the air screw and work your way up, and confirm it with plug checks. Then start with your mods. It may be that by removing the lid, you are throwing too much fuel into the engine with no place to go. Lean it out or take the pipe and silencer off for something that breathes better. Then it may come to the cylinder and head need work. Then the carb and electrics may need to be modded. Joking, but maybe you see that anything you do has great effects on the jetting. Also, by removing that lid you are increasing the sound level of your bike. Are you sure you want/can, go down this road?

 

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Hawk5443

Member

Apr 15, 2008

21

0

• Aug 15, 2008

• Thread starter
• #3

Thanks for the quick reply. Since I have purchased the bike, I really have not done anything to it other than clean and oil the air filter and change the oil. I will run it this weekend to see if re-jetting the main and dropping the needle valve down makes a difference and then I will go from there.

Thanks again.

 

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destructo

Member

Feb 24, 2006

100

0

• Aug 20, 2008

• #4

If you are at a sealevel location or as high as one thousand feet or so, try this jetting with the airbox lid off, 38 pilot, 150 main with the c-clip on the second position down from top, with your air screw turned all the way in and then back out, 1 3/4 turns out. Mine absolutely RIPPS!!!! going down from stock on the main will fry your rings, air screw adjustment makes a huge diffrence in tuning and If you have the stock 42 pilot that thing is goin to run rich as hell, smoke like crazy. Good luck.

 

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Hawk5443

Member

Apr 15, 2008

21

0

• Aug 21, 2008

• Thread starter
• #5

Thanks for the tips. I messed with jetting a little--dropped pilot jet down to a 40 and dropped the needle valve all the way down and removed the airbox lid. It is a little more peppy and responsive now. Altitude is about 1400 feet at home, but I may ride as low as 300'. The main is still stock and I have not messed with the airscrew yet, but I am sure that I will tinker with it some to try to tweak the performance. Should I re-jet the main?

 

J

_JOE_

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May 10, 2007

4,697

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• Aug 21, 2008

• #6

Definately. That's where the biggest difference will be.

 

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destructo

Member

Feb 24, 2006

100

0

• Aug 22, 2008

• #7

If you want your bike to run nice and crisp, it is largely due to the pilot jet, it meters fuel throughout the entire fuel delivery range, The magic of a 2 stroke is in the jetting! You should really love the KDX when you get it dialed in, super fun bike!

 

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JimCoCo

Member

Jul 5, 2008

11

0

• Aug 23, 2008

• #8

Hawk, you got off easy. I took off my lid and proceeded to go on a long and challenging ride. Right off, I could tell that it was running lean, especially at higher RPMs. But hey! Why bother to put the lid back on? :coocoo: At about mile 30, I boiled my coolant going up a brutal hill (so did my partner). I took a long break, but the damage must have already been done. 5 miles later the piston failed and I enjoyed a 25-mile grueling tow back to the truck. :yikes: Now the cylinder is off for repair and I'm about to crack the case to get any remaining piston skirt out of it. Oh what feeling! :bang:

 

Last edited: Aug 23, 2008

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dirtballer

Member

Aug 17, 2008

22

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• Aug 29, 2008

• #9

Jim, Do you think that just doing the airbox mod, with otherwise stock jetting, caused your motor to be so lean as to overheat? Others are saying that the factory settings are so rich that doing the airbox mod alone should not cause any concern.

 

J

_JOE_

~SPONSOR~

May 10, 2007

4,697

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• Aug 29, 2008

• #10

If the bike was jetted to run properly with the lid on it's highly possible you could cause engine damage by not rejetting after removal.

 

whenfoxforks-ruled

Old MX Racer

~SPONSOR~

Oct 19, 2006

8,129

2

Merrillville,Indiana

• Aug 30, 2008

• #11

_JOE_ said:

If the bike was jetted to run properly with the lid on it's highly possible you could cause engine damage by not rejetting after removal.

Click to expand...

Ditto!

 

J

JimCoCo

Member

Jul 5, 2008

11

0

• Aug 30, 2008

• #12

dirtballer said:

Jim, Do you think that just doing the airbox mod, with otherwise stock jetting, caused your motor to be so lean as to overheat? Others are saying that the factory settings are so rich that doing the airbox mod alone should not cause any concern.

Click to expand...

Dirtballer, I'm not sure that the airbox mod alone was enough, but I believe in combination with a piston that was overdue for replacement it was enough. My suggestion, see how it rides for the first 15 minutes and make sure that you have the lid with you! That was my big mistake. :uh: