i just bought a 2001 400ex and im looking to get more power and performance out of it. now this is what i am thinking- custom made head pipe and exhaust, port and polish, air filter, rev box, stage 2 hot cam, and maybe shave the head a little. my questions are- does this sounds like a good combo?, what are your thoughts on shaving the head?, what are your thoughts on a custom made head pipe?, and what rev box would you recommend? and im not exactly sure how to go about jetting? any input would be greatly appreciated. thanks

 

Get rid of the head shaving, rev box, and custom exhaust. Mabe go with bigger valve springs and a Wiesco piston-12:1 or 13:1 compression. With the exhaust, I would go with Curtis Sparks or LRD, or even a HMF- all full systems.

 

Man, Beastly, what do you have against rev boxes? I have used a +1000 White Bros. cdi in both my 300ex and 440ex for several years with no problems. Honda has the lowest rev limit of any quad I have ridden, to get any benefit from aftermarket parts, you need to give it a bit more rev, or with better breathing, it revs so much better, you hit the limit, and lose any gain from your go-fast parts.
Also, unless you plan on running race gas, 13:1 is a bit high for a trail motor, 11:1 or 12:1 is plenty high, that will require premium or better, depending on how hard you run it and how hot you get the motor.
Auto, head port and polish will really help, no milling unless you plan on making a racer out of it and want to buy 10 buck a gallon race fuel. A lot of pipe manufacturers will give starting points for jetting, ususally going up 1 or 2 sizes on the main is a good point to start, if you open up the air box as well, you may want to go up a size on the pilot, makes it start and idle a lot better, and helps with low end response. Your plugs will tell you if you are jetted, warm up with an old plug, then install a new one, make a hard run up to 3 gear, then kill the motor and coast to a stop, pull the plug and if it is tan, you are good, black,too rich, whiteish, too lean.

 

Ok, keep the rev box, I think mine revs up just high enough [for me], but mabe not enough for someone else. Next time anyone asks that, I'll keep my hands off the keyboard.

I think 95wolv is right on with the jetting and spark plug testing (3rd gear run). The only other way to test your jetting is just by feel, like idle in 2nd or 3rd gear then punch it, if there is any sputter or late response, you might be runnin a little rich. Or let your 400 sit with a high idle on (ziptie around the throttle), and if the header turns orange with in 1 to 2 mins, then you are running lean.

Another, cheaper way to find power is instead of going with Hotcams, try to find a xr400 cam, Honda tuned the power down on the 400ex, and one of the things they took power from was the cam.

 

thanks for all your advice this will get me started but now i have a new problem. i let my buddy take it over the weekend and he called me and said it was making a wierd noise, so i told him to check the oil and it was bone dry. of course when your in the woods and dont have a funnel, its not easy to get oil in the resavour with a gallon jug of oil. anyway he found a beer bottle and i guess it took like 5 or 6 beer bottles to fill it up. the moral of the story is now it smokes when you rev it up. im just wondering if it would be the valve seals or guides, or rings? thanks again

 

Well, now's your chance for all those performance upgrades, more than likely, he toasted the rings a bit running it low on oil, best thing is to get a comp. check,wet and dry, to see if it is rings or valves. Either way, sounds like you may be taking the head off for a valve job or new piston/rings. Usually if the motor starts making noise, the damage is done,even if oil is added right away. Sorry to hear about that,to be honest, I would see if the "buddy" who did the damage would be willing to chip in on repair. Let us know what you find out.

 

I would never bother moding an engine that old, beyond just doing the exhaust, airbox, and a rejet....

 

ok well i pulled it apart and i believe its the rings. i ordered a 440 big bore kit, im sending the head out to have the valves checked and to be port and polished, and i aordered an FMF powerbomb header and a jet kit. what do you think a good jet/needle combo would be to start with? i will be making my own tip and leaving the airbox lid off. im gonna wait on the cam and rev box do to low funding. thanks

 

oh one other questin, does anyone know the procedure for timing this thing? i marked it so i could just put it back together the way it was but somebody pushed it out of the way to get a car in, and they disrupted the wire i had keeping tension on the cam chain. oops. thanks

 

Hopefully your cam chain is still hooked up down below, or you will be pulling your stator to put it back on the drive gear. Timing is pretty easy,turn the motor over with a socket wrench until the "T" is lined up with the mark on the inspection hole. You will see other marks,an "F" I think,and maybe some hash marks. Once the bottom is lined up, you line up the cam gear (it will have a dot on one of the teeth,or a hash mark) with a mark on the edge of the cam opening on the head. then, with the cam tensioner all the way loose, you feed the chain back on, but you will probably have an easier time lining up the sprocket, then taking it off, putting the chain on, and then putting it back on the cam, works for me, but maybe someone here has a better method that works easier. Good luck, just post any questions or problems and we will try to help you out.