wr450f '04 Hesitation then pop?

On my WR450F ’04, when I crank it open from zero-throttle there is a major hesitation and then a pop and then she runs up the rpm's fine.

I just did all the mods today, gray wire, throttle stop, JD blue #4, 170 main jet, fuel screw 1.75 turns, air box lid removed, gty-r exhaust insert, 500ft, 55-70deg. The bike feels like it pulls twice as hard since the mods, but the only thing that concerns me is the very bottom like I said before. I also took out the exhaust insert completely and found that it did the same thing. Is there something that I may have forgotten and how can I get rid of this bottom end problem?

Thanks

It sounds like you may be too lean on the fuel screw, and you may need to go up on the pilot jet. Try adjusting the fuel screw out till it goes away. Make sure the bike is warm when you do this.My 2 cts!! :)

Dave

I think a 165 main, Red #5 is better for 50 - 70 degree weather at your elevation. You are jetted for 30 degree weather which I have for the winter but this is not causing your problem. You should be on a 48 pilot. If all else is the same then adjust your accelerator pump on the right side of the carb. 1/8th turn at a time. You can do this with the side cover off and run it up and down a side street. Adjust until you get the squirt duration where you like it. Chances are you are a little long on duration from the factory. Most people turn it in a little to get rid of the famous "bog". See your instruction manual for adjustment notes. :)

i agree with indy. the blue needle may be a bit much for your temp. just one clip position can make a big change in that "snap the throttle open" bog.

Thanks guys

I've been reading on the acc. pump adjustments and will start there. It wants to die after the hesitation, and that soundslike the acc. pump adjustments I was reading up on.

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It’s amazing how the mods I’ve done so far have given the bike so much more power. I didn’t notice any change having the GYT-R insert in the exhaust or the exhaust open, only louder, so I’m leaving it in for now.

I thought the red needle was for higher elevations.

You will need the red needle for temps above 60 degrees at your altitude. There has been a lot of testing with JD needles in the midwest and red #3 (90 degrees and up),red #4 (70 - 90 degrees), red #5 or Blue #3 (50 - 70 degrees), Blue #4 (35 - 55 degrees), Blue #5 (20 - 40 degrees). Of course you can use richer or leaner jetting at different temps but this seems to give the bike the best throttle response. I have ridden at over 10,000 feet on the red #4 and you have to remember that air is so much colder at these high altitudes that our hot weather jetting works perfect for high altitudes. I ran 155 main red #3 & 4 , 45 & 42 pilot in Colorado several times this summer. I love riding out there. :)

Wow, thanks for that info. That’s exactly what I was looking for…info on the needles.

I ended up adjusted the acc. pump screw 1 clock-wise turn, fuel screw to 2turns and increased the idle slightly. The snap off the bottom was better, it didn’t want to die, and the power is awesome…power wheelies in all gears. I’m going to play around with the red needle next weekend.

Would you run all those needle positions with the same jetting, if I stayed at around 500ft?

I rejet for all major weather changes and I think that is why I have avoided the dreaded woodruf key failure. My bike never started on stock jetting or without mods. If you live in the midwest and ride in the same area I recommend rejetting for each season. Spring, summer, fall, winter. That means if you dont ride in the winter you only rejet 3 times all year. 170, 165, 160 main jets for the 4 seasons. Remember to change to a 62 starter jet for summer and a 45 pilot jet. I run 72 starter and 48 pilot for the colder weather. :)

Thanks again for this info. This post has helped me more than reading 50 others. I will start experimenting using your suggestions.:)

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