Help a Yamaha newbie.

Hey Guys,


I originally started this post in the WR400 forum, as this is what I was told the bike was when it was given to me. The bike did not run when I got it so I started with diagnosing the issue by checking compression, spark, and fuel. Bike has plenty of compression and is getting spark. I rebuilt the carb but still couldn't get the bike to fire. After countless hours of research I decided to reopen the carb and replace all the jets. During the jet replacement I had a mismatched pilot jet. I started to think the bike was a different year so I looked at the vin number. According to the vin number the bike is actually a 99' YZ400F, I also checked the engine vin and it too is from a YZF. During the diagnostics I checked the timing and the exhaust cam was rotated one tooth clockwise, I didn't think much of it because I saw that the wr400 could be set to this timing to gain some extra power. Now with this being said obviously the exhaust cam is actually out of timing instead of being set up for yz timing on a wr. Does this sound right? and could this be preventing the bike from cranking? Thanks!

Edited by hattackk

Hi,I feel your pain.i would set exhaust cam back a tooth to standard setting for your yz 400. Process of elimination and getting it up to spec is the surest way. All the best.

I would  check valve specs while you are at it, and definitely put the valve timing right.

I need to verify this engine Vin. I'm getting mixed answers. When I google h308e-004813 it comes up as a yzf but I also found a database with engine Vin stating it is a 98 wr400. Can someone verify this? Frame Vin is jyah03cxxxxxx

I need to verify this engine Vin. I'm getting mixed answers. When I google h308e-004813 it comes up as a yzf but I also found a database with engine Vin stating it is a 98 wr400. Can someone verify this? Frame Vin is jyah03cxxxxxx

How about some pictures of the bike? The yz and wr are Fairly easy to tell apart visually

An old trick with WR's before auto decompression was to retard the exhuast cam one tooth, which duplicates YZ cam timing on that engine.  That would be one tooth clockwise.  If it really was a WR, then it would now have YZ timing.  If it was really a YZ in the first place, it might not even start.  Try it at the original timing marks and see how that goes.


All that said, the carb is the single most likely suspect in starting problems.

Here's what my timing looks like now. This is as close as I can get it. If I line the two outer punches with the head the crank mark will be at "Z". I've also included a pic of the bike as requested.




Here is what it looks like with the cams aligned.



Looks like it is half a tooth off. I'm going to replace it with an OEM chain anyways.

The chain is worn ("stretched").  You should replace it.

Thought I would give an update on the bike. Got the new timing chain put on and the dots lined up perfectly. I've done a valve check and they are out of spec. I'll be picking up the 3 shims I need tomorrow to get it looking good. An interesting thing I found was that there was absolutely no clearance on intake valve 3. When I removed the bucket I noticed the shim wasn't sitting in the recessed spot on the valve and not magnetized to the bucket. I would imagine this could cause some issues. I put the shim back in and the measurement was close to what I was seeing on the other intake valves. Hoping the new chain, proper timing, properly spaced valves, and a refreshed carb will get this old girl tearing up dirt once again.


PS. I also calibrated the TPS sensor per the manual, not sure how much it plays a role in cranking.

Edited by hattackk

Got everything back together. Timing and valve clearance within spec. Still no start. I'm starting to wonder if the CDI is causing the bike to fire at the wrong time causing the spark to be useless

Have you checked to see if the flywheel is indexed correctly?  Probe with a screwdriver or similar through the plug hole and check that top dead center as marked on the flywheel is actually where the flywheel thinks it is.

Yeah I was hoping that might be an issue, but the piston is actually at TDC when the flywheel indicates so. Compression and leak down test show a healthy engine. Just finished a RM250 which needed a complete engine rebuild and it has gotten back together faster and running than the one that was supposed to just be a carb issue lol. I can get it to blow a fireball out of the intake if I spray starting fluid through the intake with the throttle opened which may ignite 3 out of 8 kicks. Which is leading me to believe that it is sparking at the wrong time very advanced is what it seems like. That is why I'm thinking it may be something with the CDI/CDI Magneto. Any thoughts?

If you have access to a strobe timing light, you can check that.  Have a helper kick the bike through while holding the compression release while you watch for the marks on the flywheel.  There are two marks just ahead of the TDC  mark that should be where spark occurs at starting/idling speeds.


The other thing to look at is the quality of the spark.  It should be able to jump across an 8mm gap or better (5/16").  If not, it may not be able to fire under compression.

I did as you suggested and the bike is hitting on the H every time. So looks like it is sparking correctly. Plug is getting fuel. Now I can get it to backfire without starter fluid. I feel like this is a good sign haha. It is more than it has given me since day one. All valves are opening and closing right and timing is right on the money.

The links didn't work. What I've been doing is hold comp lever till I feel the compression stroke push slightly pass and with the choke pulled kick the mess out of it. It has a new iridium plug but I'll get another one. Outside the engine spark is blue and strong. Could a coil fire blue outside but be too weak under compression?

Gray's right about the starting drill, my 98 wr 400 was terrible to start until I learned the magic juju and then it was no sweat. On mine, I would hold the compression release while kicking until my foot was almost at the bottom (maybe 3/4 of the way) and then release at the last second. Also cycling it through a few times before trying to actually kick it seemed to help.


Edited by hattackk

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