89 KDX200 Misfire

[KDXRyder200]

I have a 1989 KDX200 and it runs pretty good except when i get up into the top of powerband near full throttle and it starts to misfire and i never reach full throttle and it is very annoying. My bike runs pretty rich first of all and i'm running Amsoil synthetic oil at a 50:1 ratio and a B8ES NGK spark plug and the plug is still black prolly because i never reach full throttle. But recently i have accidentally run it while the gas petcock was turned off and when i went to accelerate it took off like greased lightning! It hit full throttle up through 2nd and 3rd gear then it died which is when I found the gas petcock was off. But then when i went to take off down the field with the gas petcock back on it misfired again. Now me and my dad have never really messed with the jetting but we have replaced the float valve and made sure the float was at the correct level. And we have looked at the clip position and it is at the 3rd Groove which is the stock setting. Now i think the misfire is caused by a rich main jet but i don't wanna screw with jetting until i get some opinions on what the problem is. My dad thinks it is electrical but i say if it hits full throttle with the gas petcock OFF then it has to be the carb, the carb on my bike is the stock carb which is a Keihin PWK 35mm. Any advice as to what this problem is,what is causing it,how to fix it, would greatly be appreciated because i wanna put a FMF Fatty Pipe on it and a PowerCore Silencer but i wanna have the misfire cured first. All the advice and opinions that i receive are greatly appreciated! Thanx everyone!

 

[procircuit21]

They come a little fat out of the box, but it if the carb is all stock, then it shoudln't do that. Tear the carb down and make sure none of the jets or any orifices are plugged. The answer is somewhere in the carb.

 

[KDXRyder200]

for the people trying to tell about my bike u need to e-amil me at mvcjr@localnet.com because i can't access what people r trying to tell me. crazykdx e-mail what u said!

 

[KDXRyder200]

sorry i just accessed what u said

 

[KDXRyder200]

Do u think the main jet is plugged??? Cuz sometimes if i like do around a corner it will hit full throttle but just for a second

 

[JasonWho]

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[KDXRyder200]

I tore the carb apart and looked at all the jets and i have a 158 main jet and a 48 pilot jet but it was plugged with **** so we blew it out and i was already at the KDX Jetting specs and it says stock jetting for a 1989 is a 155 Main, 48 Pilot Jet, and the clip at the second position and my pipe and silencer came in so i have to buy a new 155 main jet and a new R1173 jet needle to compensate for the pipe and silencer being on and i'm not gunna run my KDX at 50:1 anymore cuz i had my dads 1992 KX250 and i was running it hard and that had 50:1 Amsoil mixed in and i blew the motor and it cost $500 to fix it. We had to replace everything from the crankpin up to the piston rings internally. And i don't need that happening to my bike.

 

[KDXRyder200]

Thanks crazykdx and JasonWho i really appreciate it! Now i can move up to beating 400EX's not 300EX's anymore! Thanx!

 

[G. Gearloose]

Ryder if you havn't already, open up your airbox; in stock form it causes the jetting to go rich at high rpms.

 

[Canadian Dave]

Idon't have any specifics on what air temps, humidity etc you're using the bike in but that jetting still looks a little too rich. Check out the carb tuning section of the JustKDX wed site and take it from there. I'm guessing a 45 pilot, 152 main and the stock jet needle in the 2nd from the top clip position is close to where you'll end up.

Given the age of your bike be sure its mechanically sound before you dig into the jetting.


David

 

[KDXRyder200]

IF i take the airbox cover off.....will splashingat high speed through puddles get water into my intake??

 

[JasonWho]

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[89kdx200rdr]

ryder
stock jetting for your bike is 158, 48, 1172n 4th pos from top. run the amsoil at 32:1, need to change my sig. no nothing will get in your airbox with the lid off unless u lay it over in a very large puddle. if you are around 1600 ft elevation u should be able to safely go with 42, 152 and 1173n in mid pos. also the stock plug is b9es.