Rebuilding 400ex due to oil burning. MODS?

[bodfper]

What simple engine mods do you guys recommend? Im not looking at spending a ton of money but what is a budget build that will make a nice reliable fast bike? Im thinking of the 416 kit with some other mods. Give me your ideas

[atv fan 28]

if you are on a budget, i would do a pipe, cam, and take the airbox lid off. this will give you a noticable increase in power.

[bodfper]

I have a dmc dual exhaust and a K&n w/ no box but im looking for a little more, like the 416 and stage 2 cam. What would the cam do w/ no bore? Also i wanted to port and polish it. What does that cost?

[BraapBraap214]

hotcams are a remarkable difference, just make sure you rebuild with wiseco. if you put in a big bore buy a rev box, just don't install it until your new piston is broken in. but that will unleash your quads full potential.

[Bill Martin]

On my 07:

P&P head
416 Bore
12-1 piston
Stage 2 hot cam
Removed choke
New pipe (you have)
174 jet

This made a big difference in HP.

I ride MX and the tracks I ride on have some big jumps that come right out of the corners.
When in stock form, no mater how hard I came out of the corners I could not clear those jumps.
After the mods I can make those jumps with no problem. If I'm not careful I will over jump them.

I'm fixing to do the carb replacement with a 450 carb.

Stay with the 416 and it will be reliable and will give you room to rebore later if you need or want to.

Stock valves and springs are fine for this mod, only replace if needed.

Stock 400ex heads are severely detuned that’s why they are bullet proof.

Remember air flow is the key to HP.

All together should run you about $1000.-1200.
Just make sure you get someone that has done a lot of 400's and know what they are doing.
I hope that helped!!!

And yes It was worth the money, I smoke 450’s all the time. Heeeee!!!!!!!!!!Heeeeeeeee!!!!!!!!!!!!!

[Bill Martin]

The rev box didn't work on mine. Went back to the stock one and it works better.

[BraapBraap214]

thats strange, maybe because of my 440? I use a big gun but that was my latest upgrade and it made a huge difference. Maybe it was the brand you bought

[tflatt]

Originally posted by Bill Martin
The rev box didn't work on mine. Went back to the stock one and it works better.
which box did you have