1999 yz400f MODS

9 replies to this topic
  • jimbob69

Posted May 12, 2006 - 05:26 PM


I recently aquired a 1999 yz400f. i LOVE the bike over all, but theres a few things i want to change about it.

It is 100% stock, and its just a bottom end monster, no top end at all really, and it must be shortshifted to use the power.

How much do pipes help these bikes top end power?
And witch pipe works well with these bikes.

Also where would if i was going to put it hotcams, is it common to do just the exhaust cam, or would you definentally go both at once, and what are these bikes like with cams and pipes together?

Thanks for any input!

  • DRH

Posted May 14, 2006 - 01:14 PM


With my 1999 400, I needed to create more bottom end. You might want to check to make sure that mods were not already done to it. As I recall, my stock 99, 400 screamed in the top end, often running out of trail before reaching the top end. I added fly wheel weight and an fmf power core 4. With this I was able to still maintain high speeds, but was also able to go slow when the situation called for it. As far as the cams go, I wouldn't think the exhaust cam alone is worth the effort or the money. I am a firm believer of whenever you open up or alter the intake or exhaust you should also do the other end. What would allowing the exhaust valves to stay open longer do if additional fuel was being pumped in on the other side. I am just not seeing a significant boost.....

  • Markopolo400

Posted May 15, 2006 - 02:56 PM


I have a stock 1999 yz400f and it has a rediculous amount of low-end.

I can pull 3rd gear in even the tightest of corner. But it really doesn't have a ton of top-end to speak of.

  • kevin204

Posted May 15, 2006 - 03:13 PM


The 400F's, from my experience, have alot of bottom end, and will rev very high, but just kind of suck air at high RPM. There isn't much power, just alot of rev's.

  • jimbob69

Posted May 16, 2006 - 06:12 PM


So what im asking sort of, Is there anyone hear that has put a pipe on their 400 and got a lot more top end pull? The way you described it as just "sucking air" in the high rpms is the perfect way to describe it. Id like it to pull up in the higher rpms. Any Suggestions/ ideas?

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  • One Louder

Posted May 16, 2006 - 06:49 PM


My 98 yz400 pulls great on the high end. It got even better when I got a new back tire. What is your sprocket combo? There is a pic of my exhaust in "my garage" It is a Big Gun exhaust system.

  • siudog

Posted May 18, 2006 - 06:43 PM


I had a '99 YZ 400F with full Pro Circuit t-4. Made it louder for sure, not much diff until I was at white knuckle speeds already anyway, but it did pull harder and longer. Save your cash and stay stock. btw, the sucking air is more like "it's revving out but I'm not going any faster" (little over rev).

  • yzrider450f

Posted May 23, 2006 - 02:46 PM


i have a 98' 400 and i have forza carbon fiber exhaust, i didnt notice much of a difference performance wise until i got high in the powerband. It sure sounds a lot nicer though.

  • theclone

Posted May 23, 2006 - 05:07 PM


My 400 makes power everywhere. It just keeps pulling from bottom to top. Most 400 owners love these bikes because of how linear the power is. Maybe there's something wrong with your bike? Jetting? :ride:

  • MIyzrider

Posted July 19, 2007 - 03:21 PM


I just picked up a 98 400 and actually think it doesnt have any lowend. Up top its got way more than i need. My gearing is stock. 14/49 (i think thats stock)
The bike also has the zyp tie carb mods, jetting is 168 main, ZT fuel screw 1 3/4 out , stock pilot , and the JD blue needle with the clip in the recommended position for sea level. i dont really know what exhaust is on it , the silencer say's Bill's in it.The bike runs great , starts easy and only lightly pops on decel (don't know if that means anything) . Now i'm new to 4 strokes, the only other thumper i've ridden was an 05 KTM525 sx with some mods. And that seemed to rip more down low. I just figured there would be arm ripping power from idle to the rev limiter but what i seem to have is a very controlable power band, once the motor revs up the bike is a rocket , but down low the bike just seems kind of mellow. i am coming off of a yz250 two stroker , so that the only thing i really have to compare too.
The only thing i plan on doing is going up a tooth on thr rear.

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