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Is the 98' faster then the 99'

14 posts in this topic

I have a 99yz400 with a 15/50 gearing for the sprockets. I run a 14/50 on the track and the 15/50 at the desert. This weekend I went riding with a friend that has a 98'yz400 with stock 14/49 gearing. Why is his top speed unbelivably higher then mine even with the 15/50? I realize that going up one tooth from stock in the back will take away from the top speed but the extra tooth up front should out weigh the affect of one tooth in the rear. I would be almost topped out in 5th and my friend would pass me barely on the gas. I would guess that his top speed is close to 10mph faster then mine. His bike is completely stock(absolutely nothing has changed on the bike since he bought it new except the oil). Did the 98' come with different gears then the 99'?

Thanks

Khris

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When in doubt, GAS IT!

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How can it be the rider when were cruising side by side down a straight flat dirt rode in 5th gear and he is able to just twist the throttle and pull away like he has another gear and I'm topped off in 5th. Even when were cruising side by side I can hear his bike is idleing in 5th where mine is at least half throttle.

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When in doubt, GAS IT!

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A few possibilities:

He doesn’t have stock gearing.

It is a WR disguised as a YZ or a YZ w/ a WR fifth gear.

A 120/90-19 may be worth a few mph, and some tires are sized differently (i.e. Pirellis seem on the small side).

As far as I know the two should have the same top speed.

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Hick,

This is thouroughly confusing me. I know for a fact it's a YZ because I was with him when he bought it from the dealer new in 98'. I'm not sure about his tire size but I am sure that he is running 14/49 gears and I'm running a 15/50. I checked with my own eyes. I also know that nothing inside the motor or gear box has changed except the oil. Is it possible that he could have got a YZ from the factory with a WR 5th? That's the only thing that I can think of. When I ride his bike it's OBVIOUS that the top speed is faster.

Khris

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When in doubt, GAS IT!

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Khris,

Possibly different internal overall ratio between the two years??

yzernie

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Khris,

I forgot to add that jetting (maim jet)could make a difference on the top end too.

yzernie

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Are you both hitting the rev limters in 5th? The only way you are not going fast enough is your bike is not reving as far in fifth gear. Now, he could be accelerating faster than you to speed. If you have a good GPS you can get your top speed with it. Test each bike sperately.

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Rick

01 YZ426F #85 Vet C

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No, we're definately not bouncing off the limiter. It's more by feel and sound. I would think that everyone that rides on open roads has a certain RPM that they like to cruise at. I determine this RPM by sound of the motor and where I think it could comfortably cruise all day at. When I hit this RPM on my bike and then again on his bike it literally feels like I'm in a 6th gear on his bike because I feel as though I'm hauling ass. I know this isn't scientific at all. It's more seat of the pants feeling but the difference in speed is very noticable. I don't know how else to explain it. Bye the way thanks to everyone that reads these posts. I think this forum is one of the best thing out there for our bikes and I'm blown away by the wealth of knowledge here.

Khris

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When in doubt, GAS IT!

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Originally posted by sirhk100:

No, we're definately not bouncing off the limiter. It's more by feel and sound. I would think that everyone that rides on open roads has a certain RPM that they like to cruise at. I determine this RPM by sound of the motor and where I think it could comfortably cruise all day at. When I hit this RPM on my bike and then again on his bike it literally feels like I'm in a 6th gear on his bike because I feel as though I'm hauling ass. I know this isn't scientific at all. It's more seat of the pants feeling but the difference in speed is very noticable. I don't know how else to explain it. Bye the way thanks to everyone that reads these posts. I think this forum is one of the best thing out there for our bikes and I'm blown away by the wealth of knowledge here.

Khris

On my recent 98, I ran 14/51, and it not only helped smooth delivery, it helped max speed. I could pull 5th to a very high rpm without hitting the limiter. It was "eye-watering fast" said my buddy who rides an xr600. I think your motor is unable to pull the taller gears and your buddie's bike is able to pull stock gearing. A good test to see if this is the problem is to get on a fast straight, get into 5th and twist wide open throttle. If all you hear is a loud, deep throaty sound with no or slow increase in rpm's, this is the problem. Your bike, if geared properly, should be able to accelerate in 5th till the rev-limiter.

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OldnBold,

Wouldn't a 14/51 dramatically reduce the top speed like what you would want desert racing. That gear would definately accelerate you to the rev limiter faster then my 15/50 but my top speed should be faster, Right? I do understand what your saying about not enough power to pull the gearing but I can still in 5th gear twist the throttle and pull back a little and the front will lift off the ground easy. It's seems like the acceleration is still really good, or at least satisfying for me.

Khris

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When in doubt, GAS IT!

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Hey Khris, hows that engine of yours? Did you ever get around to checking the top end out? :)

[This message has been edited by Hugh LePage (edited 03-07-2001).]

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Hugh,

You know I did pull the top end off. It wasn't that bad and made for good experience. Everything looked fine, valves wear adjusted correctly to start with, the rings were free in the piston. I was surprised by how clean the top of the piston was compared to my old 2 strokes. I went ahead and put it back together with new gaskets and checked the valves and everything again. I replaced the drive chain and sprockets before I rode it after the reassembly and now the noise is gone. I'm not sure if it had somehting to do with the motor or maybe it was actually the drive chain. If it was the drive chain, oh well. I got some experience wrenching on the motor further then I have in the past and now I know everything inside is good.

Khris

------------------

When in doubt, GAS IT!

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An easy test would be to put the 14/50 combo on an race him again. I think you'll be surprised.

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