Jetting a 87 kdx200 after adding a DG Pipe

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john_18837

Member
Jun 3, 2001
6
0
I have recently gotten my first dirtbike. It is an 86 kdx 200cc 2 stroke. The only things that I have bought for the $300 bike are a new dg pipe, silencer, gastank and that little circle thing with all the magnets on the inside that goes over the coil.

Anyway, My bike is not running so hot after I made these mods. The plug is always wet. I tried with the advice of a friend turning the screw on the carb out 3 full turns. I also tried moving the clip, on the carb, 2 different times down a notch towards the middle of the five notches. It did help by moving the clip down two. It is currently in the middle.

It seems as if the bike was running too lean and hot when I had turned the adjustment screw on the carb to 3 full turns from the bottom, but it was real fast. I ended up melting the silencer right off the bike. Like I said I am pretty new. I am running between 40:1 - 50:1. My friends said it is better to run with too much oil than not enough. I have tried b8es and b9es plugs. I think the bike is getting too much gas, from the wet plugs, and that the adjustment screw on the carb should be at 1/2 to 3/4 from the bottom.

Do you think I need to change my main jet? Should I go with a smaller one and how about the pilot jet? Do I need to adjust that one smaller too? How much smaller on both of the jets should i go. As far as I know the jets that are in it are stock. I finally got a second silencer and I am ready to start trying again. I really would appreciate your help and ideas.

Hopeless with a dirtbike in NJ,

:(
 
K

kyle_581

Member
Jan 8, 2001
5
0
you should just use eric gorr's "ride and feel" method to jet your carb. he has it on his site. http://www.ericgorr.com. just make sure that everything else on the bike is in good shape like the piston, rings, and reeds. for the pre mix, i would just stick to something between 32:1 and 40:1
 
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john_18837

Member
Jun 3, 2001
6
0
DO you usually have to increase the jets by one or two sizes when you add on a better exhaust pipe? that would be both the main and slow jets that would be increases right?
:think
 
S

spanky250

Mod Ban
Dec 10, 2000
1,490
1
It is more likely (but not always the case) to have to go down on the mainjet after adding an aftermarket exhaust due to the increased flow causing the engine to run rich. The KDX line has always come jetted very rich from the factory anyway.

To rejet, you first need to make sure everything is in good shape. The top-end should be fresh, the silencer should have fresh packing in it, the reeds should not be frayed or cracked and should seal flat against the cage, all the jets and passages in the carb should be clean, the air filter should be clean, and use a new plug (actually you will need several plugs
;) ).

Start with the pilot circuit. Get the bike up to full operating temperature. Turn the airscrew in until the engine starts to die, then slowly open it until you find the point where the engine is at the highest idle. If you are less than 1 turn out, the pilot jet is too small (not likely the case on a KDX), if you are more than 2.5 turns out the pilot is too big. Once you have the correct pilot jet, you adjust the airscrew in and out a small amount to find the setting that gives the best throttle response (my bike is sensitive to 1/8 turn adjustments).

The next jet is the needle. This affects the jetting from about 1/8 throttle to about 3/4 open. This one you have to do by feel. Find the clip position that gives you the best power and response.

The final jet is the mainjet. Make sure the engine is warm, and put a fresh plug in. Run the bike through the gears with the throttle wide open. When you top out in top gear, chop the throttle and hit the kill-switch at the same time and coast to a stop with the clutch pulled in. Take the plug out and look at the insulator down inside the threads. It should be a light tan if the main jet is right. If it is dark and/or wet, the main is too large.

I also like to run 32:1 oil ratio, but that is another story. Whatever ratio you use, settle on one before you start to rejet, and stick with it. I would also recomend either modifying the airbox lid for more flow, or tossing it completely before you rejet.

Hope this helps.:)
 
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john_18837

Member
Jun 3, 2001
6
0
jetting a kdx 200

I went ahead and placed the new boysen reeds into the bike. I also adjusted the timing and turned it back a little. I also adjusted the clip on the carb. The clip i am referring to is the clip with the five positions on it. I moved the clip farther towards the top of the carb. The plug is no longer wet. The exhaust pipe gets real hot though. could this be because of the timing?
The bike seems to have pretty good top end power but it is very doggy in the low end power. I also noticed that the air screw on the carb, it moves on its own sometimes when i rev the engine. I know this is not good but will getting a new screw solve this or do I just need a new spring that goes over the screw?
I appreciate everyone's help. My bike runs better because of you!!!
;)
 
J

john_18837

Member
Jun 3, 2001
6
0
jetting a kdx 200 after adding a dg pipe.

The exhaust pipe was very hot from the beginning. even before i adjusted the timing.
 
J

john_18837

Member
Jun 3, 2001
6
0
jetting a kdx 200

I found out hat the jetting was too small both the main and the pilot jet. I have since bought a new silencer and the new jets. i will try installing everything tomorrow and let you know the results over the wwekend.:D

i also found out if you advance the timing it will cool the engine.
 
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