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04 KX 250F FMF Jet Kit runs like crap

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I have a kx250f just put in a new 13.5:1 compression piston, fmf factory 4 full exhaust, K&N filter no back fire screen. took me a half hour to start the bike had a 178 main in it. FMF came with 5 mains from 142 to 160 seams way to small of a jet size whats up with that. Any ways put in the 160 with the needle povided and the 5th clip down its like 30-40 degrees out now in north east ohio. Bike wont start for crap and will only run decent under full acceleration any thing else and its missing real bad piolit is probly 40 from what every one else has stock. also some one tell me why FMF jet kit only gose up to 160 ???? HELP

Thank you in advanced

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Nope did not have to take the slide out. never touched the hot start cable either. I will check it today. what about the jet thats beside the main jet in the bowl kawasaki calls it a piolit jet may be its a leak jet. would kepping that stock with the modifications done above and being 30 degress out make me need to change that.

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if you turned the carb at all,the hot start cable could be out of its fitting.

if the bike has sat for a long period,the pilot jet is probably plugged.

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Ah yes i have turned the carb many times, I picked up #42 and #45 pilot jets and swapped the 40 for a 45 yesterday and made very little change. I will look in to the hot start cable today and will let you know how it goes.

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Hot start canle was definatly the starting issue but not the running issue i moved to a 155 main jet 45 pilot needle 5th clip down. bike hesitates at crusing throttle pretty much any thing besides wide opne or hard accelaration. what now.

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i honestly remove the dynojet kit and go back tot the stock needle and main jet.

do testing and make changes from there.

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I picked up up a 180 OEM main and installed the 42 pilot Bike will star wit the choke out, will not idle at all with the choke in and will die as soon as i open the throttle., it just bogs out.

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Also I was leaking oil, thought it was from the water pum cover oring but i looked today and it looks as it is comming from the cyilnder gasket. i tourqued the head down to spec and installed a all new gaskets maybe i will have to take it all apart agian or what.

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wasnt a jetting issue at all. I took the carb all apart today to clean it pu the FMF jetting back in because it actualy ran with them in the first place. put it all back on and still ran like crap.

Pulled the plug and the gap was crushed to almost nothing regaped and it ran great. i did notice that it started to get a lilte rough when i was riding it and now i will check the plug to see how it is burning rich or lean and adjust from there. I will keep you posted and see how every thing goes.

als the oil issue is from my waterpump cover, it was just blowing up on the crank case and made it appear as it was leaking from the cylinder.

Thank you Eddie for all your help thus far.

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Hey eddie Check this out my JE 13.5:1 piston is actually tapping the plug and closing the gap to about .10 Inch only under hard acceleration. i regaped the plug and kicked the bike over sevral times and i didnt touch it. i can shine a light in the spark plug hole and see where it is hitting it what the hell is this all about. cosmtic gaskets like oem style and oem plug :applause:

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thats not good.it either doesnt have enough piston to head clearance or the piston is machined wrong.

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JE's response as follows.

Victor,

Either use the surface discharge sparkplug or shim the plug with an additional spark plug washer to keep the piston from contacting the head at higher RPM's.

Thank you,

John Noonan

PowerSports Sales & Tech

www.jepistons.com

email jnoonan@jepistons.com

----- Original Message -----

From: Victor Paris

To: jemc@jepistons.com

Sent: Monday, March 05, 2007 7:37 AM

Subject: KX250F 2004 13.5:1 Comp Piston

Hello there I have a slight problem that I would like some input on. I bought your piston in a std. bore 13.5:1 comp for my kx250f 2004 your Part number 243642. The bike had roughly 10 Hrs on it all bearings in bottom end were good I got every thing back together bike idles good but under hard acceleration the piston is nicking the spark plug and closing the gap to about .10 inch I re gap to .30 inch and it dose it again I look down the plug hole in the head and can see where it is hitting the piston and I would like to talk to some one about this and get some clearance information. Please give me a call at the number below or reply with a number for me to call you.

Thank you,

Victor Paris

Senior Draftsman

Power Substations Inc

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