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bog when given full throttle

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Hey guys, i have an 08 kx 250f, and when i give it full throttle fast it bogs. If i slowly increase the throttle it will be fine, but if i get on the bike and pull the throttle as fast as i can, it will bog. I am using a 42 pilot jet and had a 182 jet in there, but in my FMF powerup kit it said to use 165 for my elevation. It made no difference. It was about 35-40 degrees F outside. my valves are within spec, and my elevation is about 350 feet above sea level.

ive saw flames come out once from the backfire. it also backfires like crazy, on accel. and decel.

Heres a picture of my jet (not the fmf one)- what brand is this logo?

IMAG0601.jpg

Also, heres a video--didnt know my hand was out of sight in the video, but when it bogs its when i increase the throttle fast. i rode it around for a few minutes, so it was warmed up. (recorded with cell phone, so quality is bad)

Im doing fork seals on the bike so thats why the fronts all apart.

Edited by TheBrock

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you need to do the ap mod. search for it, itll help alot with the fast off throttle bog and its free, just gotta open the side of the carb up.

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you need to do the ap mod. search for it, itll help alot with the fast off throttle bog and its free, just gotta open the side of the carb up.

im going to put my 185 jet in, but theres nothing majorly wrong with the bike then, right? just bogs when i turn the throttle fast?

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Nope, ntn wrong with the bike. the ap squirt just doesnt last long enough when going from closed to full throttle. They all come stock like that, ill try n find a post on the mod for you, its an easy fix.

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It´s not for certain the AP mod will fix this problem.

The most common problem would be clogged passages, either through the pilot jet or the Ap (accelerator pump) and leak jet circuits. The leak jet decides how much fuel goes through the AP circuit and most recommend a smaller one than stock. With a smaller leak jet the jetting will be richer at sudden throttle movements because it will "leak" more fuel back to the carb. So this jet number works backwards.

The second most common problem would be a broken AP diaphragm.

Wiring or putting an o-ring over the AP pump link is not a bad thing to do, but it will probably not cure your problems.

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It´s not for certain the AP mod will fix this problem.

The most common problem would be clogged passages, either through the pilot jet or the Ap (accelerator pump) and leak jet circuits. The leak jet decides how much fuel goes through the AP circuit and most recommend a smaller one than stock. With a smaller leak jet the jetting will be richer at sudden throttle movements because it will "leak" more fuel back to the carb. So this jet number works backwards.

The second most common problem would be a broken AP diaphragm.

Wiring or putting an o-ring over the AP pump link is not a bad thing to do, but it will probably not cure your problems.

i just bought a 45 pilot jet, it had a 42 in their so ill see if that makes a difference tomorrow

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i was trying to put the wire around the ap, but it wasnt working so my dad and i put a zip tie and it works perfectly, thanks guys

Did this fix your bog problem?

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Did this fix your bog problem?

Yea it worked perfectly, its hard to get to (well especially me cause i have big hands) but me and my dad were able to do it without taking the carb out. also, the backfire/pop went away and only does it in neutral.. i think that went away when i went up on my pilot jet. good luck

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