newbie here with a 98 YZ400F


7 replies to this topic
  • hookedonjuice

Posted February 22, 2005 - 09:50 PM

#1

hello everyone, i have been doing some reading on this site and have found out a grat deal of info, this place is awsome :)

i just got back into dirtbikes 2 weeks ago with a purchase of a 1998 YZ400F.
i used to ride and race a 94 RM250 about 8 years ago and traded for street bike. well i am back into dirt and have some questions.

the bike is a 98 YZ400F with FMF titanium 4 exhaust but not sure on head pipe, new tires front and rear, new chain and sprockets and pro taper fatty bars. paid $1800 for it.

just rebuilt carb completely, new front wheel bearing, clutch lever and grips.

i need to reseal the forks, what weight oil and do i need to change the springs for just motox testing and maybe later on some races? also i thought about changing the spring on the rear shock while i am working on it. what spring would you reccomend for me? i am 6'0 245 pounds. i want something to handle some decent jumps, doubles, step ups, whoops etc.

also i have a bad bog from off idle to half or WOT positions. it is really anoying. the jets in the carb are stock so i figure i need to re-jet. any recomendations are welcome. i also geta blue flame from the muffler when i let off the throttle, is this normal on these 4 strokes with aftermarket exhausts?

i went to the track with it last weekend and made 2 medium paced laps not really jumping to hard and i got back in the pits and barley could walk r hold up the bike, i was so fatigue after 2 laps, i never had that happen with the 2 smoke. is there something i can do to help this? suspension? engine mods? i am not it top physical shape but not a blob either i am very active but i can do the same laps on my brothers quad and i am fine and that is being very agressive with the laps.

sorry for the long post but i had alot of questions for you all. thanks for taking time to read this and for the replys :)

  • yzfxr

Posted February 22, 2005 - 11:28 PM

#2

when you rebuilt the carb did you take apart the accelerator pump bowl and actuator rod? because on the 98-99's the linkage tends to get water under the boot and rust up, so you basically have no pump action. also make sure you take out the air jets and clean those passages. if you're shooting flames out the exhaust, you're probably lean on the pilot circuit. turn the pilot screw out and see if its better, then try a richer pilot. stock is 175main, 45 pilot.

the forks take 5w. the 400 is 254lbs with gas, so it weighs more than your RM did, also the clutch pull isn't as smooth, so it may tire you out quicker at first.

  • Dano426

Posted February 23, 2005 - 07:28 AM

#3

i went to the track with it last weekend and made 2 medium paced laps not really jumping to hard and i got back in the pits and barley could walk r hold up the bike, i was so fatigue after 2 laps, i never had that happen with the 2 smoke. is there something i can do to help this? suspension? engine mods? :)


Just remember that the RM 2-stroke riding was 8 years ago. Suspension mods will help, but you will need to do some reseach and find what works best for you.

Here are two website with a ton of info that will help you out. But you will need to get a manuel for levels and torque specs for the year of your bike. That will changes from year to year

http://motoman393.thumpertalk.com/
http://www.thumperfaq.com/

Congrats on your return to the dirt

  • hookedonjuice

Posted February 23, 2005 - 04:28 PM

#4

when you rebuilt the carb did you take apart the accelerator pump bowl and actuator rod? because on the 98-99's the linkage tends to get water under the boot and rust up, so you basically have no pump action. also make sure you take out the air jets and clean those passages. if you're shooting flames out the exhaust, you're probably lean on the pilot circuit. turn the pilot screw out and see if its better, then try a richer pilot. stock is 175main, 45 pilot.

the forks take 5w. the 400 is 254lbs with gas, so it weighs more than your RM did, also the clutch pull isn't as smooth, so it may tire you out quicker at first.


yes i replaced all parts in the accelerator pump and cleaned up the rod. new accelerator pump diaphram, spring, boot, all o-rings,accelerator pump bowl o-ring, float chamber seal, new needle and seat and cleaned and blew out all of the carb ports. i will try to turn out the pilot screw and see what happens.

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  • woodworker_dog

Posted June 01, 2006 - 05:43 PM

#5

Hello everyone,

I have a seal leak at the clutch push lever comp. on a 98 YZ400F. According to the manual and the service tech I talked with, I should be able to basically pull the assembly out of the tranny without any major disassembly of the tranny and replace the oil seal, and reassemble. I have removed the screw from the plate seat and can pull the push lever up approximately 1/8" - 3/16" and then it stops. I didn't want to pry any harder/further for fear that I would wreck something internally. The tech thought it may be hung up on the bearing a bit. Has anyone replaced this seal that can give me a clue/hint as to further direction to replace the seal.

Thanks in advance.

  • DRH

Posted June 02, 2006 - 08:46 AM

#6

First I would invest in a tape measure. Set the Sag in your rear suspension then go from there. There is a chance some modifications have already been done to your 98. Using the tape measure will indicate what direction you should head. Your absence from riding may be a reason for being tired, but here is a good tip which was given to me and I have passed in on to other riders switching to the 4 stroke! Shift it! Don't try and ride it like a 2 stroke, get it in a higher gear and go. I would bet you are going around the track at nearly the shifting point the entire time. These bikes have so much pulling power you will be surprised how fast you can go when the engine isn't at its peak...Just try it! You may think you are just putten around but your speed will indicate a different story.

  • kawirider

Posted June 02, 2006 - 08:55 AM

#7

Bog=lean
As far as you being fatigued..... is there any chance that you were a few pounds lighter back when you had the RM250?

  • berudd

Posted June 02, 2006 - 11:00 AM

#8

you definitely need heavier springs front and rear. Go to Factory Connection's website and look for the spring rate calculator.





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