Choke on - Engine produces more power - Jetting?


Jul 4, 2001
Hello form..

I have a huge bog when quickly snapping open the throttle..2-3sec sputter...then she goes...
I took the exhaust pipe off and found the left exhaust valve was not operating...
Top end was taken apart and necessary parts ordered..
Prior to taking the engine apart I noticed that the bike produced ALOT more power, with no bog, when the choke was pulled all the way out and the air screw as only 1/2 turn out.
Seems to me I'm way too lean on the pilot circuit.
My question is :
I have tested with the choke on full and the air screw only 1/2 turn out and the bike runs awsome...I need a richer pilot no doubt.. How much richer do I go.
Here's my setup.I bought the bike this way.
FMF pipe/silencer
bossen reeds
air box lid removed
The jetting :
Main 150
Slide Cuttway 6.0
Needle R1172N
Clip position 3rd from top
Pilot Jet 45
Air Screw 1/2 and choke on full ( just to test) I don't ride this way.
Temp 25'c
about 150-250 m above sea level



May 17, 2000
When I installed my REV pipe I also had a bog when snapping open the throttle. I though the REV pipe just stole my bottom end but I was wrong. I tried a richer pilot and the bike ran better so I tried one more step richer and the bike got even better when snapping the throttle but started loading up when riding slowly. So I decided to put the pilot back to the recommended 42 and adjust my needle clip one notch richer.....WOW, that was my problem all along. Now my bike stays crisp when idleing and stands up when I flick the throttle open. :cool:

My current summer jetting is 152 main, 42 pilot, needle clip in #3, A/F screw @ 3/4 turns out. When the temps cool off I will switch to a 155 main.

Canadian Dave

Super Power AssClown
Apr 28, 1999
Pull the carb off , remove the float bowl and clean everything up really well with carb cleaner. Be sure to inspect the jets and insure they aren't obstructed. Reassemble the carb and check the float level.

Then . . . To get the ball rolling install a BR7ES plug and do a plug reading at WOT to insure your main jet is appropriately sized. I expect it's a little on the small size. Most 89 to 94 KDX owners will run a 152 to 158 main jet. You'll find carb tuning instructions on the JustKDX home page. Check them out. Follow the link below.

Remember its also possible that you have an air leak some where causing a lean condition. If you've never replaced the crank seals you might consider inspecting/testing them. Given the bikes age it would be a good place to start if you expect an air leak. Don't try to rejet to mask a mechanical problem.

Let us know how things are progressing.



Jul 4, 2001
Thanks for the recommendations..
I'll have bike together next weekend for testing.
Once I'm comfortable with the exhaust valve operation I'll move onto the jetting.
Thanks and I'll keep all posted...


Jul 4, 2001
Hello all.
Sorry for taking soo long getting back to the form. (too much overtime I guess)
Here's the latest.
I did indeed find the jets I was looking for.
I replaced the exhaust valves,replaced the #45 pilot with a new 48 pilot jet...buttoned the engine up and went for a ride..
Wow!! what a difference..especially after I dialed in the pilot circuit using the air screw..
I still feel I'm a little lean at WOT...The power really flattens out at the top.
I'm going to install a new 152 main and test...I also have a 155 main if the weather gets cooler...currently we are at about 15-20'c.
When I say wow,,I really mean WOW.. I near scared myself a few times last ride..
The bike pulls amazingly well right from the bottom, through the mid and the unfortunetly flattens out at the very top.
The sound this little monster makes is incredible. It really growls now.
I hope the main will clean the wot problem...if not I'll look at the timing.
thanks and I will keep all posted.
Bucket - in the dirt -:D

P.S. It'd be nice to have someone experienced riding the KDX200 take my bike for a spin...An experienced opion on how my unit is performing would be very advantagous.. I live in the Toronto Canada area and ride maining in the Ganaraski Forest.
Thanks again

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