Another Jetting Question

[4whl786]

I have a 2003 400EX, white brothers exhaust, k&n, holes drilled in the top of my air box. I put a 42 pilot jet in and a 155 main. My elevation is around 1200 feet. My problem is that it runs pretty good through the first four gears. When I am hammering on it in 5 though it bogs out. The plug doesn't look too bad, but I just adjusted the carb today. I am a newbie at jetting, so what adjustments do I need to make to stop the bogging. Thanks

[quadrider400]

Would depend if you are running stock rear tires and stock gearing... if so I would not be surprised when mine was stock I had no power in 5th.... you can drop one tooth in the front and you will find that you can manuver better in the woods and will get more out of 5th gear...

[GPracer2500]

Go up a size on your main. If the "bogs out" condition gets better then keep going until you've found what's best. If going up a size makes it worse, then go in the other direction.

Alternatively, you can temorarily cover up the holes in your airbox to richen up your jetting and see what effect that has. If covering up the holes fixes the condition than you know you are too lean on your main with the airbox opened up.

A K155 main sounds maybe a tad lean with your mods and location. Just guessing though...

Remember that the main predominently effects 3/4 to wide-open throttle--so be sure you are in that throttle range when testing your main (RPM is mostly irrelevent, it's the throttle postion that matters).

[4whl786]

I was figuing on going up more on the main, but I wasn't sure. I guess I will go pick up some more jets tonight and test it out. Thanks for the help.

[400exstud]

Originally posted by GPracer2500
Go up a size on your main. If the "bogs out" condition gets better then keep going until you've found what's best. If going up a size makes it worse, then go in the other direction.

Alternatively, you can temorarily cover up the holes in your airbox to richen up your jetting and see what effect that has. If covering up the holes fixes the condition than you know you are too lean on your main with the airbox opened up.

A K155 main sounds maybe a tad lean with your mods and location. Just guessing though...

Remember that the main predominently effects 3/4 to wide-open throttle--so be sure you are in that throttle range when testing your main (RPM is mostly irrelevent, it's the throttle postion that matters).

I was thinking just the opposite.

Take the airbox lid off and run it through all of the gears. This will lean it out but it won't cause any damage for testing. If it gets better then you need to try a 152K or 150K. If it gets worse than you need to go bigger.

[Wheelie]

What he said, you're too rich. Mine had no problem pulling 5th w/a pipe and filter.