Best YZ400F performance upgrade?

I would like to get a little more punch out out of my 99 YZ400, right now it has a white brothers silencer. I was thinking about doing a powerbomb header? I am on a somewhat limited budget so any help or input would be appreciated.

How much do you want to spend?

The power bomb header smoothed out the power curve on my bike. It will make the power come on smoother not harder, spend your money on a high compression piston or a JD jet kit. Or maybe a set of Hot Cams?

I was hoping to spend under 500 bucks. I ride mostly MX tracks and could just use a little more oomph. My dad on his KX 250 with a few odds and ends really takes me on straits, not too worried about that, but would like some more juice out of corners etc. Thanks!

I was hoping to spend under 500 bucks. I ride mostly MX tracks and could just use a little more oomph. My dad on his KX 250 with a few odds and ends really takes me on straits, not too worried about that, but would like some more juice out of corners etc. Thanks!

With a $500 budget you could get the high compression piston and a jet kit. The piston enhances the bottom to mid power and the JD jet kit creates unreal throttle response. I think you'll like both mods. :censored:

I have a DSP power now valve that I had on my 99 YZF400 (before I sold it and bought my 06) It gave a little more snap up to 1/4 - 1/2 throttle. I would sell it for $40 usd. That along with a JD jet kit and power bomb header would give you a lot of pull down low. Also think about the 6 - 8 oz flywheel and/or 1 - 2 teeth bigger on the rear sprocket. I did all of these mods to my 99 only I left the stock exhaust on it. I would out pull my buddies on their CR and KX 250 smokers and my partner on his 02 426. Also think before you go high comp piston. You will need to run a higher octane fuel and will shorten the life of your engine.

Big bore (boring the stock cylinder) will greatly weaken your motor in is crazy expensive.

If you want some well spent money on the motor. The 2000 (2000 only) 426 cylinder and piston will fit your bike. The crank bearing is different, but other than that it is a straight swap and way more reliable than big bore, high comp piston, and if put togther right, more reliable than stock.

Check out the powroll linnk above.

PM me if you are interested in the power now.

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