1998 yz400f build/restore

Got to ride the bike.  It started with just a few kicks.  Lots of popping on decel.  After some research decided might be exhaust leaks and or lean condition.  Joint from hfeader to mufflet leaks I know and there is a leak at the front of the muffler.  Drilled the rivits and took the can appart.  Packing is shot so new is on the way along with some rtv copper to seal things up.  Had an oil leak on the crankcase cover but was an easy fix.  I had let the gasket move out of place when I buttoned it up so just took cover off and lined things up more carefully.  No more leak.  Chainging oil.  Check the valve clearance again.  Exhaust seemed a lil tight the 1st time I checked it but looks to be in spec on second look.  When I get it back together I will tackel the carb settings. I'll try getting the piolt jet dialed in and then check out the needle clip position.  Lots of power but I dont think it is pulling like it should.  Had a bog to it and stalls easy when chuggin along. 

I would recommend buying new, stock size jets. They're cheap and give you the stock baseline to start from. Jets usually get gummed up from ethanol in newer fuels if left sitting and can make your pilot jet circuit run lean. For the 10-20 bucks it's worth it IMO.

I would recommend buying new, stock size jets. They're cheap and give you the stock baseline to start from. Jets usually get gummed up from ethanol in newer fuels if left sitting and can make your pilot jet circuit run lean. For the 10-20 bucks it's worth it IMO.

I may have to do that.  I tore the carb down and cleaned the jets good with some gumout so I will give it a try with what I have first.  I reset the screw to 2 trurns out today.  It is my understanding that if I go more than 2 and half turns then I need to go up a size on the pilot.  I have very little experiance with jetting but as I unserstand it I:

 

1) start the bike and get it warmed up.

2) Adjust the idle down to were it barely idles.

3) Move fuel screw in 1/4 turns. 

4) If idle goes down then that was the wrong way so go back. 

5) if idle goes up then readjust idle down.

6) when both directions cause decrease in idle you are there. 

7) finish by adjusting idle up to normal

 

Now if for some reason the pilot screw make no diference in the idle then the pilot jet is....ummm......ok now im lost....does that mean the pilot jet is too big?????

Edited by buildabike

That sounds like the right procedure.

I may get flamed for this, but my idle screw does nothing. I think I left it at 3/4 turn out. It's an aftermarket one that is easy to turn on the fly. I have minimal popping on deceleration and the new pilot jet I got cleared up the bad hanging idle my bike had. I probably need to go down a size on the pilot, but for now it's good enough for me - the bike hauls ass.

I was a bit disapointed with the performance of the bike on the initail ride but I am pretty sure the carb was not right.  I tore the card down again today and gave it a very good cleaning.  I paid a lot of attention to the jets.  Used a small wire to scrub the holes the soaked them in muratic acid for about an hour then hit them with some carb cleaner then more scrubing with the wire then more carb cleaner.  They looked new inside and out so I have more confidence.  Waiting on new packing for the muffler.  Also waiting on some graphics to help spruce up the plastics.  I'll get some pics up soon.

I got some graphics in for the bike today.  What a diference they made.

IMG253.jpg

IMG254.jpg

IMG256.jpg

IMG260.jpg

Ummmm....I think your bike might be a WR.  Large fuel tank and coolant bottle under the left number plate lead me to think it is a WR.  If this is the case you should look up the free mods for the WR to unleash a bit more power.  This could be why you feel like the power is underwhelming.  The WR's were essentially a restricted version of the YZ.  I think there were throttle stops and something about a grey wire mod...I'm not sure because I don't have one, but you should look into this.

Ummmm....I think your bike might be a WR.  Large fuel tank and coolant bottle under the left number plate lead me to think it is a WR.  If this is the case you should look up the free mods for the WR to unleash a bit more power.  This could be why you feel like the power is underwhelming.  The WR's were essentially a restricted version of the YZ.  I think there were throttle stops and something about a grey wire mod...I'm not sure because I don't have one, but you should look into this.

It's definitley a YZ according to the VIN.  And there was no WR in 1998.  Someone along the way did put a lot of WR parts on the bike.  18 inch rear wheel, coolant overflow, and some of the suspension components appear to be from a WR as well.  I wish it was a WR so I could have lights but no such luck.

Finaly got the bike finished.  A new pilot jet did the trick and it runs great.

IMG282.jpg

IMG270.jpg

IMG268.jpg

IMG279.jpg

IMG278.jpg

IMG272.jpg

That looks really really good. I wish i had the know how to do stuff like this. I have a 99 400f myself that is in nowhere near that kind of shape. Anytime it has an issue, which hasnt been often since the rebuild, i have to take it somewhere.

Thats is looking so nice man you should be proud a lot of progress there

Just curious, how much have you got sunk into this thing? ive put i figure about 800 bucks into mine, and none of that has been making it pretty lol

Just curious, how much have you got sunk into this thing? ive put i figure about 800 bucks into mine, and none of that has been making it pretty lol

I had about 1400 in it.  Traded it for 700 bucks and a 2006 suzuki eiger atv.  Used the $700 to buy new plastics, wheel bearing and brakes for the atv.  The book value on the 4wheeler is around $2700.  So I should be able to flip it for a good profit.  Im ready for another bike.  Much more fun to work on and play on than the atvs.  I have my eye on a 98 xr250r for my next build.   Just gotta get this wheeler out of the way 1st.

Oh Man! Nice job.You have inspired me.Found one on Craigslist for $750 with valve trouble.Think I will go buy it.I also have a XR250r and think I will make this YZ400 my winter project.Hope mine turns out as nice as yours.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now