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dirtbike_newb

New Guy...99 YZ400F

14 posts in this topic

First of all I want to say hi and from the looks of it this place seems to be really helpful. I've been on sport quads for about 10 years with plenty of dirtbike experience, just no ownership. I just bought a yz400f Tuesday and am looking for any advice you all are willing to give. Its got a K&N filter and PC T4. I'm still gonna check on the jetting, its got a little pop on decel so I might go up on the pilot.

I also have a few questions.

- Can I adjust seat height by reducing the preload on the rear shock? If so, how much. I'm 5'10" and a couple inches would make a world of difference. I'm mainly gonna be on trails and the previous owner was always at the track, so I'm not worried about it being too soft.

- How long can I expect to run on a tank of fuel at a medium pace (fire roads)? Should I look into an oversized tank?

- Do you guys recommend any decomp cam over another (yz450 vs hotcam...etc)? I've got the drill down, but it seems the cam will make it much easier starting.

- What other recommendations do you have?

I love the power of this machine and can't wait to get better acquainted with it.

Here's a few pics

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Thanks!

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- Can I adjust seat height by reducing the preload on the rear shock? If so, how much. I'm 5'10" and a couple inches would make a world of difference. I'm mainly gonna be on trails and the previous owner was always at the track, so I'm not worried about it being too soft.
You could, but you shouldn't, because the rear sag setting affects not only the operation of the rear suspension, but the steering geometry as well, and thus, how the bike behaves in corners and in the rough.
- How long can I expect to run on a tank of fuel at a medium pace (fire roads)? Should I look into an oversized tank?
between 30-35 miles, depending on the gear you're in, and a host of other factors.
- Do you guys recommend any decomp cam over another (yz450 vs hotcam...etc)? I've got the drill down, but it seems the cam will make it much easier starting.
It will. The OEM 450 cam is what I recommend, but there are reasons to go either way.
- What other recommendations do you have?
Get rid of the K&N filter, and replace it with a good White Bros. or Twin Air. Buy a Scotts oil filter and clean it with every oil change.

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Okay, from what I've read of the 96 pages of the cam mod, there are differning opinions on whether or not to run the 450 decomp cam. I dont want to wear out a chain, so I'd rather pay for the right thing. Does anybody have any evidence either way on a 98-99 400?

The sag thing makes sense, the lower I set the rear, the more caster I'm putting into the forks and the slower responding the steering is. But will this make much a difference for a rec rider, not a racer?

What is so bad w/ the K&N? Will a dual-stage foam work that much better?

Thanks for the info, I'm still getting used to taking my feet off the pegs (against my quad instincts) so be patient with me.

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But will this make much a difference for a rec rider, not a racer?

well if you take corners hard at all you will probably feel a difference my bro's seat is cut down and it is awesome so if you think your comfortable with cutting or shaving foam them you should probably try that

What is so bad w/ the K&N? Will a dual-stage foam work that much better?it is probably the worst air filter you can get for your engine all the dirt it let through is horrible for the valves and wears them out way faster than they should

Thanks for the info, I'm still getting used to taking my feet off the pegs (against my quad instincts) so be patient with me.my brother has the opposite he got his foot stuck under a quad tire going about 20 while making a turn and flipped it :thumbsup:

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... there are differning opinions on whether or not to run the 450 decomp cam. I dont want to wear out a chain, so I'd rather pay for the right thing. Does anybody have any evidence either way on a 98-99 400?
No one has worn out a chain any earlier using the 450 cam, and there are guys who have run them long enough to warrant replacing the chain anyway. No problems.

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Thats good to hear. I've seen the Hotcams listed for about 160, how much can I expect to pay for the 450 cam? Is 03 the right year to fit my bike? Also, where can I buy the 450 cam? I've checked ebay, but only hotcams.

Thanks for the replies and the great information.

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Seriously. Get rid of that K & N filter. I use both twin air and Unis. K & Ns will let dirt into your engine.

Clarke makes a nice fitting 3.3 (i think) gal tank that you could probably get 75 miles out of. I can go 75 with some reserve at 6000 feet altitude (leaner jetting) with my 2.8 gal.

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What is so bad w/ the K&N? Will a dual-stage foam work that much better?

Also, where can I buy the 450 cam?

The K&N could actually filter better than foam. If you look in the test that is being touted as damning K&N's, the Uni in the test did even worse. But there are a couple of things to consider. First, if it's an older element, it will have no media on the back of the filter around the wing nut, and those older ones are somewhat more restrictive than a foam filter.

Second, and this is the real problem, they are almost impossible to oil properly. That's what gets people into trouble with them is that they don't either get them clean, or get them oiled over 100% of their surface and down into the media, mostly because of the pleated construction of the filter. Otherwise, they work OK, but to me, they are simply too hard to get right.

It should be stressed, however, that a foam filter is only as good as the oiling it got, and they need to be kept cleaner than a good many of us seem willing to do.

You could buy your 450 cam through the ThumperTalk OEM Parts Store. It will cost you $10 to join, but that will be wiped out by the savings on the camshaft alone. In your case, though, you may want to look elsewhere, since they don't list the YZ400.

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First of all I want to say hi and from the looks of it this place seems to be really helpful. I've been on sport quads for about 10 years with plenty of dirtbike experience, just no ownership. I just bought a yz400f Tuesday and am looking for any advice you all are willing to give. Its got a K&N filter and PC T4. I'm still gonna check on the jetting, its got a little pop on decel so I might go up on the pilot.

Congrats on the YZ! I bought mine new and still have it. It's been the most reliable dirt bike I've ever owned. Believe it or not, my valves are still within spec AS IT CAME FROM THE FACTORY! Haven't had to shim them yet (but admittedly I don't ride it much, maybe 6 times a year or so.)

You're on the right track with pilot jet; go up and decel pop will diminish.

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After looking through that filter test, it seems their results show the UNI as being the worst of the bunch as far as filtering small particles goes. The UNI had a longer time until max restriction, but that was probably because all the dust that would normally be causing a restriction was passing right through it. It also shows that the K&N does require more frequent cleaning because of its short time to max restriction, but I clean mine nearly every other ride. If I were to base a decision off of that test, I'd have to be a fool to switch to a UNI. I am an engineer and nearly every bit of data from that test shows the K&N superior to the UNI. The scaling on the filter efficiency graph also makes the K&N appear worse than it is. It's only a little over 3% less efficient than their best filter in the test, and only a little over 1% less efficient than the UNI. However I do know the K&N's aren't widely known for their superior fine particle filtering. That is why I've run one with an outerwear for nearly 3 years on my modified yamaha warrior engine and its been totally reliable, doesn't smoke, and is as powerful as the day I built it. Most of its running time has been in very dusty conditions.

I believe the main factor in maintaining performance and prolonging engine life of these types of engines boils down to maintainence. Keep the oil changed, the valves in spec, and the filter clean. In my experience this has resulted in a reliable and high performing engine despite an "inefficent" air filter.

Sorry for the long post and thanks for the advice. I really appreciate all your help.

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Give the TT store a call for the cam. Even though they don't list your bike they may be able to get your parts. I have a 98 WR400 and have been told they can get my parts.

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