Good news, bad news. HELP!!!!

Good news: The dealer double checked my YZ timing / Valve work and decided that I did it right. The only issue is the exhaust valves may be a smidge loose (clearance should be 25mm to 30mm and a 30 will fit if jammed in there.)

Bad news: We still had trouble getting it started.

History, I live in the altitude of Denver. I changed to YZ timing and did the valves at the same time. Bike ran fine before. Runs for crap now. I put the Baja designs jetting kit in the carb (175 main, 48 pilot, DVR needle clip #4, air screw 2 out).

Today we focused on the carb. The plug was very wet when pulled a couple of times. We decided to change the jetting to the following: 170 main, 48 pilot, DVR needle clip #3, air screw 1 3/4). We tried again, it eventually started after we turned the idle screw ALL THE WAY OUT. It ran for a while, about 3 minutes. Then it would die and it would be hard to start again.

We noticed the following about the fuel line. I have the IMS YZ tank which moves the fuel cock to the right side. I reversed the fuel cock so the knob faces the engine. The fuel line then runs behind the engine between the carb and to the carb connect point. The gas was not getting a constant flow. There is quite a bit of air in the hose and some times the line would run out and not refill properly. Could this be the problem? Do I have some kind of vacuum problem. I am still hearing an exhauling noise that appears to be coming from the air box when kick starter is depressed. Also, we noticed the kick starter seems easier to move now without the compression lever pulled in. He tested compression and I'm getting 150 lbs.

Anyone have any thoughts on this problem. I am desparate. The little time it was running it just sounded so much more powerful and I am dying to try it out.

Thanks for all you input, Doug


Dougie, '99 WR400

Mods: Race Tech Suspension, YZ Timing, FMF PC IV, FMF Hi FLo Moto, YZ seat, IMS 3.3 tank, One Industries Graphics


I had (still have) a Honda CB-750F. I routed my fuel line wrong also. I had a big loop in it and it was air bound. The bike was running super lean. I ended up destroying the valves. If the bike was in my house now, I could hang clothes on it, much like exercise equipment. But alas for poor Yorric, it is parked in the garage collecting dust.

I'd get that kink out of your fuel line. Try to get the air out of it. The only way is to lift the tank up to straighten out the hose, and the air should vent out (hopefully).

That is my two cents.



I think I hear the sound you're talking bout if I try to start my bike with the seat off.

After I did my FMF PC IV, IMS tank install and rejet it was about midnight, I took the bike out in the driveway just to see if it would dice. I came back in the morning and it ran fine. I'd just washed it, so I though I just got something wet, but it acted like fuel starvation.

Did you fill the tank? with the tank full you shouldn't see any air in the line once you flush the line. Try removing the fuel line from the carb and running some fuel into a can. Mine flowed really well after the first little bit.

If that's okay, with a COLD bike you could pull the drain plug on the carb and make sure there is plenty of fuel flowing in the bowl. That would help rule out a stuck float. But it sound more like a "too much" fuel rather than a lean problem. My understanding ( Clark straighten me out if I'm wrong ) is that at closed throttle to 1/8 throttle your're just on the pilot jet, the only thing that has an effect here is the Pilot Jet and Pilot Jet screw ( aka, fuel screw, air screw ). Once you get to 1/8 or so the needle comes into play, main jet is the player from 3/4 to full throttle. If you want a detailed write up on how to jet a bike from scratch go to :

This is eric gorr's tech site and he gives a very detailed account of how to Jet a bike and exactly what jetting problems are caused in what circit.

If you got compression and spark, it can only be fuel.

Good hunting and let us know what it turns out to be.


Chris in the Mojave

'98 YZ400F

Kevin, there is no kink in the line. It has to run up and over the carb link up at the engine. So there is more of a "small hill" effect. The gas just won't flow smoothly. We've tried running it all kinds of ways this way. I am wondering if I have to run it around the front of the engine. Hey, would the vent tube make a difference. The IMS gas cap came with it's own vent hose, but I am using the stock WR vent hose. I noticed the gas caps are different and maybe the IMS cab needs to use its own vent hose?


Dougie, '99 WR400

Mods: Race Tech Suspension, YZ Timing, FMF PC IV, FMF Hi FLo Moto, YZ seat, IMS 3.3 tank, One Industries Graphics

I use the IMS cap with the stock Yamaha vent hose. You realise that the plastic thing in the hose is a one way valve, put it in backwards and fuel won't flow out of the tank, kinda like putting your finger over the end of a straw. On my IMS tank I put the petcock on with the handle facing out and the hose outlet facing forward, I then just run the hose around front behind the radiators. Here's what you need to do first... remove the 14mm plug from the bottom of the carb to see if the float bowl is full or not. While it's out you can turn on the petcock and see if fuel starts flowing out of there to check flow.


'99 WR400

'92 GSXR 7/11

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Take off the float bowl main jet access nut turn on the gas and make wure you get good constant flow. Fill up a 2 lb coffie can if you have to. If the flow stops or becomes intermittent then check the following things. 1) run fuel into a can right from the fuel line it should flow freely. 2) the vent tube must flow air freely into the gas tank through the gas cap or you will have problems. 2) remove the gas tank and take off the gas cap and turn it upside down and strain the fuel through a strainer into an funnel into a gas can. make sure there is no crap in the tank. 3) remove the petcock and make sure there is no debries on the petcock filter tube inside the tank. 4) get a longer piece of fuel line and run it forward up over the top of the engine and back to the carb and put the petcock on so the valve faces outward. If you now have consistent fuel flow. Then proceed with the jetting.

Remove the float bowl from the carburetor and make sure that when you changed the pilot jet 1) its screwed all the way in and did not fall out and 2) when you put the little white plastic piece back on the needle jet tube YOU GOT IT ON STRAIGHT AND ITS NOT HOLDING THE FLOATS DOWN or otherwise miss aligned. Check all the friggen vacuum hoeses and make wure they are connected correctly. Make sure the throttle stop is aligned with the throttle pull pulley!!

As for jetting if above 6500 feet I start with a 45 pilot, DVR #4 and a 175/178 MJ. Now carefully seat the fuel screw and make sure its all the way in and then turn it out 2 turns.

As a side note make sure your compression release lever is adjusted properly and there is a little free play before it engages the exhaust valve!! Also pull off the spark plug cap and stick a slot screw driver in the boot hole and make sure the plug engagement cap inside the boot is screwed in tight. Clockwise for tight like any other screw. Install a new plug and put the plug cap back on and make sure it completly engages the top of the plug use good straight down force.

OK we have good fuel flow good initial jetting selected all vacumme hoses hooked up both front and back carburetor boot clamps tight no hang up on the compression release, and our NEW spark plug connected.

Of course you re-activated the Cam Chain tensioner after your cam timing change? the CAM chain is tight and not slack?

Now start that puppy with the choke on and absolutly NO Throttle twisting. Maybe bumup up the idle adjustment via the idle adjustment knob.

Starting to run out of ideas but I can tell you my WR fired on the second kick after I switched the cam timing and it still is a easy starter.

hope this helps

Please keep the forum informed of your progress. I will be home this weekend and would be happy to discuss this with you.

661 259-1048


Thanks guys, I will try it all. I am really anxious to get on this thing.

Clark, about the idle knob, we had to turn it all the way out before the bike finally started. So it is adjusted as far as it will go. Hey how about if I fly you out for a look over. Probably be cheaper. :)


Dougie, '99 WR400

Mods: Race Tech Suspension, YZ Timing, FMF PC IV, FMF Hi FLo Moto, YZ seat, IMS 3.3 tank, One Industries Graphics

The exhaling sound that you described on your WR after you switched to YZ timing sounds exactly like what my WR did when I went to YZ timing. I noticed it right away the first time I tried to start the WR with the new timing. I know that I made the timing change correctly. I did have some difficulty starting bike, but changing to a 48 pilot jet corrected the starting problems.

It runs hard and I have had no problems with the engine. I'm sure it still has that exhaling sound, but now I'm used to it and can't really distinguish the difference in the exhaling sound anymore.

I run the stock exhaust with a Vorip insert and the bike is stock quiet. Perhaps I noticed the exhaling noise because my exhaust does not drown out as much engine noise as an aftermarket pipe.

Good luck and let us know what happens.

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