2003 Xr400, looking for best Preformance Upgrades, and get to spend my friends money to do it !

[upbart]

So here it is, my friend has a 2003 Xr400, he also has another xr400 maybe a 2002 that his son has taken over. Between a group of us there is about 6 xr400's but this one xr400 that his son has taken over is just faster than all the rest, I am thinking it has a cam in it, but no one knows for sure as it was bought used and has never been apart. My friend wants his bike to be faster than his sons bike, so he is coming up north to my place in a few weeks riding with a groups of us friends. But he is going to leave the bike with me and he wants it faster than his sons bike, money doesn't seem to be a object as he has plenty of it. I am looking at doing a cam, and a pipe, going to look at the piston, may have it bored and new one if needed, will be rebuilding front and rear shocks, and going through the complete bike.

I am looking at the best cam for low to mid range.

Same with the pipe, want the best performing one.

Not sure if the 400 runs a chrome bore or not, never had a 400 apart, but I have a large collection of other xr's my self so I am very familiar with Xr's

I know the pumper carb is a hot upgrade, ? is how much difference does it make? not sure if he wants to spend to $400 on it but maybe.

Is there any thing else I am missing to make this  bike faster? It is primary used for trail riding so the top end isn't as big of a issue as low end, I am very mechanical so nothing is a challenge for me to do, and have most all tools and equipment to do it.

 

[scott_01_xr400]

pumper carb

[Trailryder42]

Take all the plastic bodywork and anything else that visually differentiates his bike and sons bike apart from each other and swap them in secret. Easy peasy, his bike is now faster than his sons.

 

But, if that isn't feasible, I agree, Mikuni pumper. You can spend money on aftermarket exhaust, but just doing the full intake and exhaust Gordon mods flow very well, so unless one just wants the bling, save your money. These would be the quickest and easiest power mods without getting into the engine. Then if it's still not enough to satisfy, I guess a cam would be next.

Edited July 2, 2015 by Trailryder42

[michigan400]

No chrome bore. If low end and mid range boost is what your after,,, like the ole saying goes there is no replacement for displacement. Get a 440 kit. You can get an entire kit, including a new jug with 440 sleeve pressed in, piston, rings and a gasket set on ebay for about $350. Bore ios matched to supplied piston so it's a bolt on kit. 10% increase in displacement and more power for less money than a full exhaust system.

 

Actually, just a bump in CR will also help quite a bit. Cheaper route would be a 405 or 416 overbore with a stage 1 or 2 hotcam. Open up the airbox and exhaust along with it and that should for sure make a big difference. 440 would have more torque but the smaller bores will probably drag race just as fast if on hard ground with good traction.

[BOAB]

Yep, big bore, best bang for your buck.

[some guy]

Everybody says big bore but a 416 with a 400ex aftermarket cdi will let it rev higher and will put out more h.p

But more compression and stage 2 cam is a given

I crammed an fcr,37 on my xr

But a 39 will wake it up too

[upbart]

I like the big bore kit idea, going to spend $80 to have it bored any ways, and some where around $150 for a piston, not far off from the cost of a new big bore, and could always resell the stock one on ebay, then may a cam also, will be replacing the timing chain for sure any ways, still might do a pipe and maybe a pumper carb. What is the benefit of the pumper carb for this bike, so I can sell it to him? Thanks for the input.

[Dwight_Rudder]

I am going with the 440 kit.  Lectron Carb. (Pumper carbs work well but suck on fuel economy and are not altitude compensating). Exhaust is last mod to make. Gearing also is a good mod. Go with 15/48 gearing.  Stock is 15/45.  Good O or X ring chain. Moose XCR brake pads by DP Brakes.

[upbart]

I always buy the best chain that there is, just not worth destroying your case. I will look into the lectron carb no worrys on altitude in Mi they call a hill that is 500' tall a mountion here LOL. I am liking the 440 kit idea a lot

[michigan400]

Pumper best for low end snap and throttle response. Makes cold starting way easier than stock unit. I Run 17.5 pilot and 130 main and get 48 mpg dual sporting. But thats easy with the throttle out on the road. Pumper is optional,, if you can tune a stock one well its not a huge difference.