YZ400F AutoDecomp Mod

7 replies to this topic
  • Chief

Posted June 28, 2009 - 04:59 PM


I have a '99 YZ400F that I have decided to keep and put some new life in it.

One of the mods I've decided on is the AutoDecomp cam.

I've read everything there is on here about it, but I still have a couple questions I'd like to get the answers too before I start.

I've decided to use HotCams products and would like to know if I need both Intake and Exhaust cams, or do I only need the Exhaust cam?

Also, does ThumperTalk still make the Decomp Plug?
I've looked in the ThumperTalk store and have been unable to find it.


  • aj_yz426

Posted June 28, 2009 - 05:40 PM


Only the exhaust cam is needed for auto-decompression. Not sure on the plug, I just used a freeze plug.

  • DeeCee

Posted June 28, 2009 - 06:23 PM


I did the auto decompression mod to my 400 but used the 03 YZ450f exhaust cam. Works great. You only need to do the exhaust cam. As for the plug they are not made any more, I think I got one of the last onces they had in stock. You could take the decompression cable insert to a machinist and have them machine one out of a piece of aluminium for you. Other wise as suggest by aj_yz426, just use a freeze plug.

Good luck with the mod, it most certainly makes life a lot easier with the 400.

  • 02WR426Cali

Posted June 28, 2009 - 06:28 PM


You can also just keep the decomp. lever in there and not use a plug. Keep it stock how it is, or grind off the lever portion and make it look more like a plug either way it will seal the oil out and work just as well. I ground down the lever and kept it the same lenght just made it round on the end, works great and looks good enough for me. It's not a show bike it's a dirt bike.

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  • buzzgrizz

Posted June 29, 2009 - 04:11 PM


http://www.thumperta...ight=decomp mod

here should be all the information you need the freeze plug works great by the way and is super cheap.

  • grayracer513

Posted June 29, 2009 - 06:32 PM


The freeze plug size is 18mm, BTW.

  • Chief

Posted June 30, 2009 - 02:09 PM


Thanks for help everyone.

Another quick question, will an upper triple clamp for a '00-'03 YZF work on the '99?

I found a good deal on a Pro-Taper Superstock upper:


  • rracjc

Posted June 30, 2009 - 04:49 PM


just need the exhaust cam, i did my 426 and its awsome not haveing decom lever

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