2000 WR400 will not start?

I've had the bike a while and pretty much can fire it on the first shot every time. I did the grey wire mod Saturday and the bike ran fine (the grey wire on my bike was in a two pin connector with a black/white wire). It seemed to have a low end stumble afterwards but was noticably snappier and I'm assuming once I advance the exhaust cam that'll fix itself. Anyhow, raced sunday - no problem, washed the bike and started it up - no problem. Got home last night and wanted a ride so I filled up the tank and tried to start it. I had a couple pops out the exhaust but basically nothing happened. I wore my leg out, tried with choke off, etc. Waited a couple hours in case I flooded it and still no luck. One thing I am wondering is when I filled the tank normally I leave an inch or two of air at the top. This time with the full feul jug I ended up topping it off. Will this cause some sort of vaccume lock and should I bleed off some of the feul then retry? I don't think it's the grey wire mod since it did run fine Sunday. I appreciate any help, thanks.

Mods that would matter are 48/170 jets, FMF titanium pipe w/mid pipe, !grey wire and YZ426 tank).

- Joe

Check your plug too see if it fouled!!!

As Mayday advised change the plug, your problem will be solved.

Thanks guys, I have a spare and will replace tonight. If I can get it done with a little light left I might even get that ride in!

- Joe

You guys were right, the bike started right up after putting a new plug in it. With that said, there's a new 'problem' (or not?).

The old plug was black - very black. It was a couple months of Sunday riding old so I wouldn't expect it to die so quickly. I noticed when twisting the throttle on the stand that a puff of black smoke would come out at the first hit of the throttle. I've never noticed this before and from the plug and this I know it's running rich now. Before the grey wire mod it was running just right. I wouldn't think the timing would affect my mixture like this - could there be something else I'm overlooking? Perhaps with the timing advanced it doesn't burn all the feul as quickly? Perhaps I got some bad fuel?

When you started the bike after washing it. How long did you leave the choke on? Did you let it warm up completely? Was the bike ridden or only let idle?

I used to have your problem from time to time and now I start the bike, count to 10 and shut off the choke, let it warm a bit and then circle the block. When I'm half way around, I shut off the fuel, roll into the garage and let it idle until the fuel runs out.

Never had the problem since.


When I'm half way around, I shut off the fuel, roll into the garage and let it idle until the fuel runs out.

Me too...... :)

I let the bike warm up for 2 minutes or so. I usually leave the choke on the first minute then let it idle with choke off the 2nd minute. I also rode it down the road a little before parking it. Although I don't drain the feul after each ride, usually no more than a week goes by between rides with the usual being I try and ride every couple days even if it's just for 20 minutes after I get home from work.

Is there any chance that advancing the timing via the grey wire mod and not advancing my exhaust cam has created some situation where the mixture is unable to burn completely? And lastly, should I just put the grey wire back and call it quits or should I start fooling around with my jetting to lean it out?

- Joe

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