98 yz 400f help

4 replies to this topic
  • heinzee

Posted February 02, 2006 - 07:04 PM


Ok first I know i'm going to beat a dead horse, but I did a search and did not find what I was looking for. Just pick up the bike it's like brand new the only mods are the bars, triple clamp, and white bros e- series with twelve disc. When the bike is running and I wrap the throttle it dies. If I easy in to the throttle it is fine. The jetting is stock and i'm not sure about the fuel screw I'm going to add a T-handle fuel screw tommorow. Do I need to re-jet? If so what should I go with. #2 What should I do for the postion of the fuel screw?

Thanks for the help.

  • MotoGoalie

Posted February 03, 2006 - 07:04 AM


You'll need to do some basics.

Change out and put fresh gas in.
Put a new spark plug in.
If needed pull the carb and clean it thoroughly.

Tell us more.

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  • tom nolan

Posted February 03, 2006 - 08:21 AM


Sounds like the accelerator pump is clogged. Pull the air filter and while looking down into the carb, open the throttle and see it your getting a squirt of gas. If not, than you need to address it. I think you can get a diaphragm kit and replace it. I have a 98 yz400, It's the best bike I have ever owned.

  • grayracer513

Posted February 03, 2006 - 09:04 AM


Pull the linkage cover off the carb and watch the accelerator pump shaft as you open the throttle to be sure it isn't hung up by the dirt that can get built up around the point where it enters the carb.

Also, be sure you aren't asking too much. Even when they're set up right, big thumpers will not take an instantaneous snap of the throttle without at least stumbling hard. Learn to "roll" the throttle open. Roll it of idle a little slower, and open it farther and faster as quickly as the engine responds. When you train yourself to do this, it will become second nature. You'll do it without thinking about it at all, and the engine will respond in a way that will seem instantaneous to you and everyone else.

  • heinzee

Posted February 03, 2006 - 09:13 AM


Thanks for the advise everyone. Any jetting advise:

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