Engine acting up '98 YZ400F

Brand Yamaha Yamaha YZ400F 1998

4 replies to this topic
  • bjm904

Posted May 19, 2014 - 06:13 PM


I have a 1998 Yamaha YZ 400. It has run good since I have owned it. At the end of last season the engine started acting up. It has no power at all. It idles good but when any load is put on the engine It starts misfiring and backfiring and will barely move. I have checked the spark plug for fire, checked all the jets and carb, all clean and seem to be operating normally. I have drained the oil and there is no metal filings in it. Prior to this issue, the engine was running hot and would overheat. Thank you in advance.

  • bjm904

Posted May 20, 2014 - 07:43 PM


any help?

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • Slow and Jerky

Posted May 21, 2014 - 04:09 AM


My first thing would be to put fresh gas in it (make sure to drain the bowl), check the exhaust make sure you don't have some sort of restriction. Any time I hear that something will idle but no go I think about the old potato in the muffler trick from high school  :devil: Dirty jets or maybe an accelerator pump gone south are also likely candidates.

  • Yz400f Jeff

Posted May 21, 2014 - 12:32 PM


Sounds like the problem I had when I forgot to put my accelerator pump rod in... Maybe yours is plugged up.

  • grayracer513

Posted May 21, 2014 - 01:33 PM


You say it started this before it was stored?  Check the vacuum release plate on the carb slide for cracks or missing pieces from the corners.

Related Content

WR Camshaft Swap Info - last post by jamesm113

WR Camshaft Swap Info

  • 0 replies

2014 YZ250F Electrical problems.. Stumped. by jase12

Dirt Bike   Make / Model Specific   Yamaha   WR/YZ 250F
  • 2 replies

My YZ720 Big Bore 724cc by bigbirdh2

Dirt Bike   Make / Model Specific   Yamaha   Yamaha 2-Stroke
  • Hot  30 replies

Stewarts on Yamahas? by Mongo134

Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  60 replies

2014 YZ 250F Electrical problems. by jase12

Dirt Bike   Make / Model Specific   Yamaha   WR/YZ 250F
  • 3 replies

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.