1998 WR400f Project guidance appreciated

HI, the name is Dev. I recently traded up from a 1996 yz125 to a 1999 YZ400f. The trade was straight up. The 400f was supposed to be leaking gas out of an overflow in the carb and it needed a rear tube. To make the trade seemed like a no-brainer to me. I jumped right into my little project. i ordered a rear tube. And I took the carb completely apart, cleaned and reassembled it. I installed it on the bike. And tried to fire her. I got a couple of back fires out of the carb, that's it. for me that hinted towards timing being out. So, I checked on the cams (which were supposed to be hot cams, they turned out to be stock)..long story short I realized that the intake cam gear had spun on the cam shaft. I ordered I new one. At this point I figured that i might as well disassemble the top end to inspect. The top end is fresh, but since I have the cylinder off i figured I'd give it a quick 5-10 second hone, and lap the valves before i put it back together. So, that's where I'm at with the meat and potatoes.


But the fun is only beginning. 


The wiring on the bike is/was hideous. There was electrical tape everywhere. I decided to clean things up and inspect/improve all of the connections under the electrical tape. Upon inspection i found a lot of dead end wires that had bean cut and taped off. And it seemed there were way too many wires to be an mx bike..and I found a voltage regulator on the steering stem. On the opposite side of the CDI box. I immediately thought "this is a bleeping WR". I ran the VIN and it turns out the bike is a 1998 WR400f. It was a pleasant surprise for me..too many reasons to list. I continued with my electrical maintenance. I tested everything coming out of the stator. all was in spec (on the high side). Then, tested the primary ignition and secondary ignition.


Primary spec is .20-.30 ohm. I came up with a 1.0 ohm. 

Secondary spec is 9.5-14.3 Kohms. I got 16.27K


So, both are out on the high side. Should this be replaced and could it be causing me problems or have the potential to?

The plug wire where it connects to the boot is wrapped in electrical tape due to a tear. So, replace right?


I have a ton more to cover once I get the top buttoned up. Like getting lights back on the bike for starters. And Im not to familiar with the FCR carb.

But that's it for now. Any help and guidance from some more experienced WR guys would be greatly appreciated. 


Oh, and i found some wires coming out of the case right where the transmission would be (they to had been cut off right after plugging into its counterpart). what are these wires?.

Let's keep this going, I have a similar situation with my WR. It is a 2000 model, just got it. It was in sorta rough shape but seems to have good power. So far I have installed a new rear tire, chain, front sprocket and front brakes. cleaned and lubed various things. It runs ok but seems to have the high idle problem. I played with the fuel screw and idle adjustment a bit to no avail. I'm about to check the valves and will be taking apart the carb as well. My latest discovery is that the coolant reservoir is empty and the hoses aren't connected to anything. They instead were just routed into the air box? lmao, good stuff.

I'm under the impression that the motor is getting an abundance of air. May be an air leak, or the choke isn't working properly, or too small of a pilot jet? Just a shot in the dark.

I decided to put a new sleeve in my cylinder and I installed a new intake cam. Set valave clearances the best I could. My gauges only went down to .008. I put a new coil on it also. The bike still will wouldn't start, not even bump start. So I went out and got smaller gauges. I'm going to clean the carb for the tenth time and set valve clearances tomorrow. It has to start...

I've read a couple different things about cam timing when it comes to the yz vs the wr. But my manual says the two dots on the outside are to be level with the head. And I read that there are supposed to be 12 pins in between the 12 0'clock dots on each cam gear for yz timing. That's how I have mine setup. Not that it matters. The bitch doesn't run.

Waiting on a new cdi, this has to be it. Everything else is perfect. I tested it and if I did it right the old cdi is shot.

But I think for wr timing you retarded the exhaust cam one tooth. I'm almost positive. Look into it.

Have you tried starting it with the standard timing (13 pins?)


I'll take another look at my exhaust side, are you talking about the Position A or B?

I haven't. I did some research haute a few minutes ago because you had me curious what the stock wr timing is. And I was gonna come back and tell you that regarding the exhaust one tooth is to achieve yz timing at 12 pins. So wr timing must be 13 pins. But looks like you beat me to it. I haven't tried it. But I will when the new cdi comes in.

I also, found some guys are running 14 pins in between. They are leaving the exhaust alone and regarding the intake a tooth (clockwise). They say it rips. Give it a shot.

What's yours right now?

A or B? I don't follow you.

Also, out of curiosity, what jets do you have currently? I'm pretty sure mine are an 82 and 45. I'm not sure of the main at the moment, mainly because it doesn't start, so I haven't got to the main yet lol.

'A' or 'B' in reference to my post. It shows two different timings.


I think mine are the same, I don't have the carb with me but I will check probably tomorrow

Edited by madriders86

Ok. Got ya. First, the "A" isn't correct for WR timing. The intake should be level with the head and there should be 13 pins between the 12 o'clock marks on the cams.so the exhaust 9 o'clock mark should be below the head and one tooth retarded in that pic.

In position "B" you look dead on. The marks look level and you are 13 pins between 12 o'clock marks. How did it run at that setting...if it's just the camera making it look good from my angle you should look into new cams. I had that issue. The gear spun on the cam.

Thats my worst fear, but I'm wondering if it's the cam chain being stretched? Others have told me that the chain being stretched could throw off the punch marks. The lobes look good in that position to me. The picture was taken at a slightly high angle, as you can see if you look closely. So the punch marks do not align perfectly but they are close...I am going to see how it runs as it is now. I have turned it over a bunch by hand and nothing bad has happened yet lol.


I'm just waiting on a new slide plate for the carb before I can see how it runs. I highly suggest you inspect yours closely, they tend to crack on the 98-99 bikes. T6061 billet ones like the one I'm getting are still available and are supposed to not break.

Mine actually has a crack in it. I looked for a new one and couldn't find any for sale. Where'd you get yours?

Ebay. Mine had cracked through, all the way around: https://imgur.com/a/45DIq




There are two versions of the part. I think for a 98 the "L" is the one, but contact the seller and he will help you determine which one you need. You will also want a new damper/seal/oring for it probably. He is on TT as well and you can find some info on the plates if you search around.

Edited by madriders86

Wow. I just learned something. I was looking for the whole throttle slide. But it looks like those just bolt on to the actual slide or something to that affect?

No there should be no bolting of anything. The round part of the plate just sits in the round recessed part of the slide carriage.

Edited by madriders86

Did you get the slide plate?


I got my bike started yesterday. After I reassembled it and tried to start the bike there seemed to be no compression. This is weird because even when I had the valve cover off slowly kicking it over to check that my timing wasn't completely wrong the lever would come to a point where I could stand on it and it wouldn't go further without the comp release. After much kicking the bike started up briefly then died again. I went through that process several times and finally the compression returned. Really weird. Kicking it feels normal now, like it was before I took it apart  :bonk:


Rode it around the block a couple of times. The bike accelerates nicely, but seems to bog, stumble and miss at low RPM/low throttle opening (hard to tell exactly which). When  reassembling the carb I did break off a small piece of the plastic "splash plate" baffle thingy. Related?

I couldn't get it to start back up after I stopped it. Tried again today with similar results after playing with the fuel screw a bit. I want to ride it long enough to get the engine nice and warm so I can adjust it accurately. I rode it and slowed down at the end of my street to turn back around and stalled. Couldn't get it started again. I pushed it back to the house and pulled the spark plug. Black and wet. After cleaning it off and drying it the bike starts up easily, but the plug seems to foul quickly. Not sure how to proceed...


When I got this bike the AP rod was disconnected. The bike ran ok other than the fact I couldn't get it to idle properly. I suspect I may have fixed an air leak in the process of cleaning the carb and replacing various bits. I'm wondering if the bike has been jetted to run without the AP?


Too late to start this thing up currently but I'll be back at it tomorrow. I'm determined to get this bike to run right :banghead:

Edited by madriders86

I haven't even purchased one yet. I'm taking it one step at a time. I'm still waiting on the CDI box. And then I'll go from there. I'm gonna try all combinations with the cams.

Do you think the cracked throttle plate would hinder my bike from starting?

I'm under the impression that the motor is getting an abundance of air. May be an air leak, or the choke isn't working properly, or too small of a pilot jet? Just a shot in the dark.


Do not change jetting if the bike ever ran well with the jetting it has now.

Do all the mechanical restorations to the carb first, before changing jetting.

Slide plate seal, needle jet, apump diaphragm, etc.

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