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yz450f needle position or pilot jet causes problem

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Hey fellas to cut a long story short, 05 yz450f with a full jardine exhaust system otherwise stock.

i was running stock jets (45/165) with clip in 4th position from the top (nflr needle).

thought i would richen it up a bit because of the new exhaust which i thought breathes better so i put in a 48 pilot and put the clip in 5th position from top.

Now from 1/4 throttle onwards when i hold it steady it surges/misses pretty bad

My guess is it is running a tad too rich on the needle? i put it back to 4th position but i wont be able to ride it for a couple more weeks

any ideas?

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also when i ran it with the needle in 3rd position from the top (got mixed up which was richer or leaner) it was backfiring/popping when letting off the throttle

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Put the pilot back, a new exhaust makes nearly no difference on the idle circuit. Also, the same with the needle, put it back. I bet you bike would run even better on the 3rd clip position. Running a bike so rich to reduce backfiring tends to slow the bike down

Often, the only change is needed to be done to the main jet.

But.......... Simply changing jetting because you guess is the wrong way to go. Test, change test.

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Yeah it seems im finding that out now lol

Id just rather have it a tad richer than a tad lean but obviously its not what i want lol

thanks for the help

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Would the pilot effect the bike at steady throttle surging/missing?

I put the clip back to stock and took for a ride but it still seems to do it, maybe even worse or i could be just taking extra notice now...

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Your pilot affects closed throttle to 1/8th. Your main jet will be the culprit. i would go back to your original setting....45/165 and the 4th clip.

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I have put it all back as it was

thanks

I might try unplugging the tps to see how it goes like that

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