new piston?

[vroom]

hey guys i bought my 01' 400ex yused from a college kid... it is pretty fast, but my friends stock 2003 400ex beats mine badd ( im not talking about riding skills, im talking like accel, top end ect..). I think he didnt break it in correctly and just ran it to hell and back the first day he got it. So... here are my options:

1. buy a prolite piston and gasket kit and just throw in a new top end myself

2. have a dealership hone it and put a new piston + gasket kit in to have a fresh cylinder to work with.

3. buy a 416 kit and send out my engine to be bored, honed and all that good stuff which would cost me big bucks :rolleyes:


which one should i do.. or if you have any other options im all ears :macho

[member]

3 cuz then the guy with the 03 ex wont beat you anywhere until he mods his:macho

[member]

o and one more thing you dont have to send your engine out to be worked on.. just take the cylinder off and take your piston up to a local machine shop and tell them to bore and hone it for you.. then put it all together yourself.. thats what my friend did with his at least

[vroom]

ehh 3 is really not what i was hoping for, i don't want it to be crazy fast i just want it to be freshened up and run smooth again

bump?:rolleyes:

[member]

ok then 2

[2004TRX450R]

well first do a compression test on it and see what kind of condition the engine is in. You can have two brand new bikes and both will run different. He may have just got one that runs really good from the factor. Also there are other things such as rider weight, gearing etc. that will effect the quickness/speed of the bike. If you put a new piston in it you may end up needing to bore the cylender anyway. Usually if it is worn to the point that it is running bad you will need to. Also you might want to check the condition of the valves. That can have a big effect on runability as well.

[vroom]

yeah i know, i think it mgiht be the compression, however the valves sound mint, no clicking or any noise of that sort fro mthe engine and it has stock sprokets

[2004TRX450R]

I mean check the valves for leaks. Make sure they aren't leaking past the seats and makeing for low compression. Also if they are to tight that will cause less compression as well and less power.

[Aceman]

Like 2004trx450r said do a compression check. If its low squirt some oil in the spark plug hole. If it comes up on compression plan on boring/honing for a new piston. If the compression doesn't come up your valves are leaking. Then I would do a solvent test on your valves.

[cals400ex]

1st, your running 18 inch tires. this will make you have less speed up top.
2nd, make sure your throttle cable is adjusted properly. this will make a big difference through the gears and up top.
3rd, i see you have a few mods done. jetting can make it or break it for you. what jets do you have in there now???

[vroom]

the tires aren't 18's anymore, they are 22 mudsharks... 2 - then trottle cable slack was really short when i got it, so i adjusted it to make it alot longer. 3 - i dont know what jets are in there right now cause i bought it used, i know its a k&n power kit but i have no clue what jets are in there, :rolleyes: but the spark plug is usually black and fouls alot.. does that mean im runnign rich or lean?

[Ryan]

Originally posted by vroom
the tires aren't 18's anymore, they are 22 mudsharks... 2 - then trottle cable slack was really short when i got it, so i adjusted it to make it alot longer. 3 - i dont know what jets are in there right now cause i bought it used, i know its a k&n power kit but i have no clue what jets are in there, :rolleyes: but the spark plug is usually black and fouls alot.. does that mean im runnign rich or lean?

Your running to rich. You need to find out what jets you are running. Are they stock?

BTW, 22in tires will give you less acceleration and more top speed. Since you switched to 22in tires, I recommend changing your sprockets.

Im not familiar with sprocket ratio's, though. Maybe someone else can help you out on that.

[cals400ex]

that still makes sense with the tires. i put bigger tires on my ex and i not only had slower accerleration, especially noticable in 4th and 5th gears, i also had slower top speed. i know this totally goes against what is suppose to happen. here is my thought: the bigger tires are heavier than stock so, i didn't have enough power to pull them to more top speed than with the factory size tires. who knows, maybe if i was on a road 3 miles long, i would have pulled more top speed. i personally like the stock size tires because smaller ones will give you less in the upper gears, and the taller and heavier ones also give you less because the bike has to pull more weight.

for the throttle cable, you want it short. just make sure when you turn fully to the left and right, your cable doesn't stretch enough to raise the idle. i would say about 1/4 to 1/3 of an inch of slacke should be good. if there is too much slack in the throttle, your carb won't fully open under WOT. this will slow you down.

if your plug is usually black, it is running rich (too much fuel or in other words, too big of a jet). the thing is, it might be rich on the pilot jet, needle, or main jet. this is what we need to figure out. it would probally be best if you take the carb off and see what size mainjet and pilot jet you have in. also, check to see where the clip on the needle is located at. by the way, rich jetting on the mainjet will definately slow you down. we should be able to get you in the ball park with your jetting if you tell us what is in there. also, you mention you have a jet kit in there. the mainjets and needle is different from the factory keihin parts. what i am saying, a 150 keihin mainjet is NOT the same as a 150 dynojet (the jets that come in a jet kit). also, the stock keihin needle is not the same as the dynojet needle. this will play a big role when others are suggesting what size jets to use.

[vroom]

wow thanks alot for the info man... well I talked it over with my dad and a few buddies of mine and Im prolly gunna go through with the malcoms 416 kit and maybe a slight port job.. I really don't liek buying used machine's but this was a steal at 3 grand with a brand new helmet. Once I send out my cylinder Im gunna get it rejeted by a shop cause i have no idea how to do it.

[cals400ex]

just remember, with just a piston, you won't notice much power increase. you will need a cam to complement the piston for the power to be enhanced. i wouldn't get a $75 port job either. find out whats involved there. if your not buring oil, its probally not time for a rebuild. however, a cam and piston make a nice power increase.

[acold7dusta]

check ur bearings first, before u did anything. When i checked my bearings, one was shot more times than abe lincoln. when i replaced it, it went 10x faster. it was real slow and i couldnt think of the problem, i wanted the exhaust, big bore, everything, now im satisfied, just from the bearing:p

[vroom]

guys i just put the bike up on it's rear grab bar and i was checkin the way the tires spin. The disc brakes catch in one part because they are all a bit bent. the tire spins fine until it hits the bent part and then it slows down almost to an immediate stop. this happens in the rear tires as well.. could this slow me down?

[cals400ex]

you better believe it. i would replace any rotors that are bent. how much it slows you down depends on how bad it is rubbing. if its not rubbing too much, a simple upgrade like aftermarket heavier tires can slow you down just as much or more.