98 yz400f cam mod

11 replies to this topic
  • frankllynn

Posted February 19, 2008 - 08:59 PM


Do anyone know for a fact if advancing the exuast cam one tooth on the 98 yz400 will change it to wr timing or better yet has anyone done it?

  • grayracer513

Posted February 19, 2008 - 09:10 PM


Yes, it will. The mod can only be done on engines equipped with manual decompression. Do this in reverse:


  • frankllynn

Posted February 19, 2008 - 09:37 PM


Why can I not find any articles or threads where people have done it.
I see no reason for it not to work, but I'm no engineer. I would love to here from some people that have done this and what changes they felt.

  • grayracer513

Posted February 19, 2008 - 10:31 PM


It does work (again). You don't hear much about it because most people don't want a YZ400 with less power.

  • frankllynn

Posted February 20, 2008 - 04:17 AM


Good point. I am looking for smoother power

  • Dano426

Posted February 20, 2008 - 07:15 AM


Good point. I am looking for smoother power

Then leave your cams alone and do a search on flywheels. A much better option.

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  • Dano426

Posted February 20, 2008 - 07:16 AM


Check out this post


  • jayh300

Posted February 20, 2008 - 07:27 AM


i have purchased a 10 oz zip ty for mine... i will post back results after i get it and install. me thinks i will like it

  • frankllynn

Posted February 20, 2008 - 07:33 AM


so what would the wr timing do fro the yz. All the power is a 1/2 throttle and up. I would like to have better lower rpm power even if I loose some of the upper rpm power

  • grayracer513

Posted February 20, 2008 - 09:33 AM


It does not so much give more power at lower rpm as it makes the lower rpm performance smoother. In fact, if anything, it detracts from the power across the board. It will be happier to run at 2000-3000 rpm, but it will be less snappy and more sluggish overall.

It's not an irreversible mod, in any case, so you can try it and see how you like it at no cost or loss, other than your time.

  • frankllynn

Posted February 20, 2008 - 12:21 PM


Thanks guys. Thats what I was wanting to know

  • frankllynn

Posted February 21, 2008 - 09:26 PM


Well I changed the timing..Pretty easy mod if you dont drop the key into the motor. Not a considerable difference but worth the money $0.00

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