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Can Someone HELP me having jetting issues?


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hey i have a 2000 yz 250 that i put a fmf pipe and silencer on. i have had problems ever since with 5th gear. seems like its not getting enough fuel its skipping sounds like yaht yaht yaht. fmf told me to go up on main jet by one size but ive tried going up and going down nothing gets rid of the problem. bike has brand new top end and v force reads i just put it. was having this problem before those aswell tho. iam about 500 feet above sea level. and iam getting really sick of messing with the bike. i also put a new float valve needle in the bike because i was told this could be the issue. but was not. CAN SOMEONE HELP ME PLEASE!! and like a dummy i threw out my stock pipe.duhh

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If you have tried one size larger jet, and one size smaller, it might not make a large enough difference to notice....with a v force and a pipe, you might be 4 sizes off.

But eliminate the other things first. I chased a jetting issue like this once for half a day. My bike just felt like it was not getting enough fuel. I found out why. It was not. A bunch of varnish had built up in the petcock and no fuel would get through. I've also had bad spark plugs act like this. Since this problem happened after the silencer went on, look inside the silencer for a plugged core. FMF and quality control are sometimes two terms that should not be used together.

Your fuel to oil ratio effects jetting. What ratio are you using? If you are using a 50:1 ratio or something like that, you might be MANY sizes of jets away from right. In that case, 1 step might be too small to feel.

Aftermarket products often force you to become a jetting expert and it sounds like you are on your way! Dont give up! Did you do ANYTHING else when you installed the silencer? I had a guy bring me a bike once that he put a pipe on and coudl not get it jetted right. He told me he had just cleaned and oiled the airfilter, so I never bothered to look at it. Well, 5 main jet changes later, with no results, I decided to check his work. Turns out he did clean and oil his filter, but he used the entire bottle of airfilter oil on his filter. Obviously, thats why they made it in a 1 pint container.LOL....You get the idea here. Eliminate ALL other causes before going to the one you know least about.

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hey thanks alot for the reply i think the highest i went up was 2 or 3 sizes of main jets. i will have to try higher than a 180 i think thats the highest i went. it did seem like the problem is not as bad as b4 with a 178 jet which is only one size up from stock. and yes the only thing i did was just the pipe and silencer when this issues started. iam running 40-1 on my gas ratio. i just dont see it being anything else other than a jetting issue. ill have to pull the pipe off and check but i did look in the pipe and make sure it was all clear everytime i put it on. ill check the silencer as well for a pluged core. seems like it is not with how much exauhst flow there is. and what is the petcock where is that located? thank alot for your help cheers

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OHHK so i went all the way up to a 188 on my main jet and iam STILL having the same issue? im thinking i may have tranny issues. that is 5 levels above stock on the main jet and still same problem. could this be a tranny problem? i think i may have to bite the bullet and take it into a shop....or just ride it and say screw it!! who needs 5th gear anyway right? hahah my bike still takes down all my buddies bikes without 5th gear anyway. i tell them all the time they shoulda bought a yz hahah

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ya i dont think FMF ever knows what they are talkin about when i called them and talked to them they told me two different things. but they said i should need to go up by one size on my main jet which would be a 178 but nothing seems to work i think i have other issues. but it just makes no sence because this problem started as soon as i put the fmf pipe and silencer on? wish i had my stock pipe and silencer then i would know if it was the bike or the pipe. i think i may have tranny problems but it only does this is 5th gear which which everyone says is messed up??wouldnt it give me problems in other gears if my tranny is *****... i dunno iam ready to give up!

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When i first put on the pipe and silencer(turbine core 2) i left the stock jetting, 178 main, 50 pilet the bike ran great but on top end in all gears it felt very flat. So i installed the 172 main and it was perfect. Now im around 2000 ft above sea level. It it doing this in all throttle ranges in 5th or just Wide Open Throttle?

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In what RPM range are you having this trouble? That can really decide what you need to adjust. Just changing the main is only one part of the equation. To adjust your low end range you can start by using your air screw, and from there trying different pilot jets. For your mid range you need to focus on the needle and the clip position. I know FMF often recommends more than just a different Main Jet.

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the bike screams in 1st all the way threw 4th hits the powerban and just tears cant even keep the front tire down just like it should. soon as i hit fifth just past 1/4 throttle it starts skipping yahht yahht yahht yahht. im thinking i have other issues i dont see how just jetting would do this. im thinking i got no fifth gear in the tranny. fmf told me to run stock pilet which is 50 and pin clip on third position. told me to go up one size on my main. nothing gets rid of this problem?? i think it was just bad timeing for a gear to go rite after i put the pipe on. i also noticed metal shavings a few times when i change the tranny oil. i think guy b4 me was running the wrong oil in the bike aswell.

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