The YZ400 is not that great a bike!

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#1
Pick up any motorcycle magazine today and they'll tell you at length about what a fantastic machine the YZ400/426 is. Sent down from heaven on a beam of blue light, the Yamaha has it all; speed, agility, and most importantly, it has four separate strokes. It's true; everybody likes to twist the "loud handle" on a YZ. They look good, they sound good, they are sure fun to wheelie and they do accelerate like crazy, but is this machine really the phenomenon that everybody seems to think it is?  Or more realistically, are people just thrilled that the motor vehicle industry started to upgrade the technology of dirt bikes?  I may be the only one, who feels this way, but to me, the YZ400 is a long way from being the perfect fourstroke, much less the perfect two-wheeled missile that everyone seems hypnotized into believing. Let me explain why.

I hold dirt bikes up to be measured by three fundamental rules.

Fundamental number one is this; weight always hurts you; it never helps. With all the advancements in our sport in the last decade, how everyone can make such a fuss over a bike that still weighs nearly 280 lbs wet is just beyond me. When you look at the complexity issue, and then factor in what it does to the weight of the machine, it is even clearer that the YZ is not the heaven-sent perfect bike. You know your buddy that's totally into mountain bikes? He spends hundreds and hundreds of dollars on lighter parts just to save a few GRAMS! And we load our dirt bikes up with about every gizmo that the engineers, (or is it the sales department) can think up. In 1975 we had dirt bikes that weighed less than 200lbs, don't tell me that we can't design one today. Really, if you use a chromemoly frame, keep the engine's overall size down by using a three or four-speed tranny, and make an effort to design things smaller and lighter rather than the other way around, it can be done. I'd enjoy seeing some exotic metals like carbon fiber rods and ceramic pistons; maybe even some Ti now that Russia is selling it for far less money. What is the weight of a stock YZ engine now, something like 90 lbs? Let's try to get that down to about 50, (which is still 10 lbs heavier than a 250 twostroke). Then see how it feels to fly on a bike that's only 210lbs, rather than 280.

Fundamental rule number 2 is that complexity will always return to bite you in the ass. Take a look at the YZ engine for a minute. Five valves, two cams, a computer controlled carb, and more wires, hoses, and gadgets than my Ford van. Friends, what we need in a dirt bike is much less of this unnecessary over engineering and a return to dirt bike simplicity. More parts means - more parts to break.  Our shop sees tons of bikes for broken gizmos.  Was Yamaha was just trying to impress us with their technology, rather than design a really innovative and practical engine? If so, all they got was complexity, not new technology. The formula car guys are experimenting with rotary drum valves that don't reciprocate at all, so there are no cams, valve springs, etc to adjust, wear out, or to limit the revs. That's a prime example of a simpler but more advanced system. I'm not advocating a return to the XT500, but sometimes I think that would be better than what we've got now. Look at the old 84 Husky 500 fourstroke. It used a twostroke bottom end, and it didn't even have an oil pump, but it ran hard and lasted forever. They ran the oil up the cam chain, and all the top end parts were roller or needle bearing mounted, so it didn't need much oil anyway. And I know there's a big debate about whether fourstroke carbs need accelerator pumps or not, but the roller-flat-slide carb on my YZ makes me nauseous. Honestly, if you were going to have all the 3D mapped ignition curves, wouldn't you be better off with fuel injection?

Fundamental rule number 3 states that if you're going to build a fourstroke, make sure it has a fourstroke powerband. As any YZ400 rider knows, if you don't keep it spinning it's going to stall, usually in the middle of a crowded turn or at the bottom of a hairy step-climb. I even ride twostrokes like they're fourstokes, using a high gear and lots of throttle opening, but the YZ400 is one fourstroke that must be ridden like a twostroke. It has very poor power down low, and it makes most of it's power up higher than God intended fourstrokes to be revved.  The key to acceleration is more about how much power you can put to the dirt, not how much peak power you can build. I've had the pleasure to ride a few factory built 250 supercross bikes, and they're the opposite of what you'd think. They were all bottom end and tractability, and as flat as Kansas on the top. They would have made the most fantastic trail machines ever because they were so easy to get traction and so fast out of the turns. This is more what I expect out of a fourstroke, and I'll absolutely guarantee you that built the right way, a fourstroke can rev no further than 7000 rpm and still accelerate faster than any twostroke on the track. If you look at the original Vertimati's, they had two and three speed gearboxes, and it's said that they only needed 1st and 2nd for starts; they could race they entire MX course in third, and they kicked ass on the twostrokes.  Just close you eyes and imagine THAT kind of wide tractable torque. It'd be fun, right? Not much like a YZ400, is it? I rest my case.

My point is this; Yes, I think the YZ is the best fourstroke on the market today, and it's not likely to be challenged anytime soon, even by the Cannondale (don't get me started on that!). But what we want is not an 11000-rpm street bike engine in a frame with long suspension and knobbies.  What we need from a four stroke is simplicity, lightweight, and tractability above all else. So while I'm out riding on my YZ, I'm still searching the heavens for another beam of light.


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Pete Denison
A-Loop Offroad, Inc.
“The Artists Formally Known as Moose Offroad” www.aloop.com
&lt;p align=right&gt;12-07-1999 :Edited<p align=right>12-07-1999 :Edited
 

JonA

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#2
Very interesting and honest post.&nbsp;&nbsp;It's refreshing to see another rider questioning the Gods that be.&nbsp;&nbsp;I have ridden 2-strokes all my life and just recently decided to step it down a notch and buy a '00 XR400.&nbsp;&nbsp;Granted this is no rocket, nor intended to be to my knowledge, but I think the powerband is more like what you are describing.&nbsp;&nbsp;Compared to my RM250 it feels like, well a trail bike. But I took it on the track for the first time this weekend and if my lap times were any slower I would be surprised.&nbsp;&nbsp;Like you said, I put it in third and rode all day.&nbsp;&nbsp;No wheel spin, no mis-timed hits, no arm-pump, just a damn good time.&nbsp;&nbsp;I would hate to try and get a holeshot on this thing, but it would be a different story on a KTM520 I'm sure.&nbsp;&nbsp;I must admit I have never ridden a YZ400, but I did have one chase me for 5 laps and never get by.&nbsp;&nbsp;I think the Euro manufacters may use the YZ400 as a catalyst to take 4-strokes to the next level and then we will have a true dichotomy in motocross.&nbsp;&nbsp;Jon
 

Jake

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#3
I gotta go with the weight issue!&nbsp;&nbsp;My WR is NOT a light bike.&nbsp;&nbsp;If you think about the physics involved, weight is critical to both MX and trails.&nbsp;&nbsp;The more weight moving forward, the harder it is to turn.&nbsp;&nbsp;Why was it Shane Watts was riding a KTM 125?&nbsp;&nbsp;I'm sure it had something to do with its ability to turn.&nbsp;&nbsp;The magazines are written by riders not physics majors (I doubt any even took physics!).&nbsp;&nbsp;They are always comparing horse power to weight.&nbsp;&nbsp;That's great for holeshots, but not for the turn!&nbsp;&nbsp;

Another FLAME on weight is that newer bikes are getting taller, moving their weight even higher.&nbsp;&nbsp;Granted, I sure like the 12" of travel, but this effort has its problems, too.&nbsp;&nbsp;I’m not even crazy about the camel backs.&nbsp;&nbsp;Once again, this moves weight higher.&nbsp;&nbsp;&nbsp;&nbsp;I like the factory Vermoti (sp?)&nbsp;&nbsp;I saw in one of the magazines that actually moved the gas lower on the frame.&nbsp;&nbsp;I think they moved the air box up front and the gas lower under the seat.&nbsp;&nbsp;I’d also like to see more tool packs and bags lower on the frame.

Any comments?

Jake
 

Rich Rohrich

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#4
Interesting post Pete while you are entitled to your opinion your logic leaves a lot to be desired.

Point 1 - Weight. The YZ4 should be lighter, but given the expectations of the buying public it's unrealistic to use precious metals to decrease the weight, while increasing the costs. If you do,Yamaha (or anyone) ends up in the position where buyers start complaining about the cost (like the Cannondale naysayers). It's a balancing act that's tough to win, Yamaha struck a good balance. On the up side, if you spend time on the bike you find you can't feel the weight unless you are picking the bike up after a crash.&nbsp;&nbsp;Given the target audience they made the right choice.

Point 2 - You advocate simplicity and then suggest "rotary drum valves", a totally unproven technology with a monsterous price tag attached. Then you go on to use the "84 Husky 500 fourstroke" as an example of a simplistic design. I'll agree it's simple, it's also one of the most unreliable, under engineered abortions to ever roll on two-wheels. Kettering said it best "The price of progress is TROUBLE". Moving ahead requires some growing pains, just like Simons forks, and Fox Air shocks advanced to the excellent stock suspension we have today. We had XRs and loved them, we have the YZ4 and most of us feel we got our moneys worth, and the next generation should prove to be even better.

Point 3 - If you want a flat torque curve to ride around in the woods, pop one of your cool A-Loop kits on an XR and grin for hours. I for one applaud Yamaha for having the balls to build a real race motor instead of another warmed over trail bike. AS for not having any low end, you're doing something WAY wrong if you can't lug a YZ4 with a stock pipe, correct jetting, and the correct fuel. The masses are convinced that you have to put a pipe on every four-stroke, and clueless aftermarket companies guys are more than happy to build one, no matter how much it screws up the powerband. It's a versatile incredibly rideable motor in the hands of a C rider like me, and a serious weapon in the hands of someone who can really ride. People who expect it to be an XR will be disappointed, people who expect it to be a CR will be equally unhappy.

I'm no YZ4 zealot, but the simple fact is it's the best performance per dollar value in a four-stroke race bike (ubtil the new Honda and TM arrive) you can buy today. It's reliable, cheap, and fun.&nbsp;&nbsp;Anyone who believes that it will be better than a well developed two-stroke 250 is kidding themselves.


&nbsp;&nbsp;

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Rich Rohrich
Applied Fluid Dynamics
rrohrich@interaccess.com
www.eric-gorr.com
 

380EXCman

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#5
Spelling "vertemati" (I almost bought one) TM is the one who is experimenting with the fuel tank airbox swap. Hey rich what is your first impressions of the new KTMs, with what has been written thus far.

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More to follow im sure.....
 

380EXCman

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Also I had a 98 DR350 that I put a big gun pipe and silencer on. It made a world of difference. Jetting it was an ordeal ended up I had to go 5 up on the main and 3 up on the pilot and I cut the top of the airbox off. It was like night and day . Sold the bike to my brother and he really likes it. Its not as "fast" (using the term loosely) as my 380 but for that matter a yz 400 is not either. What do you think about the big guns and is the performance gains more dramatic for say a dr350 than a yz400. I look at the yz's head pipe and silencer and it looks like it would be very useable. I rember my dr's stock pipe and it was about as big around as a quarter. just thought I would get your take on this.

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More to follow im sure.....
 

Rich Rohrich

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#7
I'm excited about what KTM is doing. They have always been able to build excellent four strokes, they just had the unfortunate habit of making them too tall and WAY TOO LONG for anyone but the dessert guys. Now that they have redone the engine and put it in an aggressive chassis from the two-stroke side of the house we should finally get to see what KTM is really capable of.&nbsp;&nbsp;a friend of mine is a KTM dealer who will also be selling Cannondales so I'm hoping to get a chance to take both of them apart sometime in the near future.

As for pipes, the old days of taking a stock pipe and increasing the ID and shortening the header are OVER. The new generation four strokes are designed as systems not parts lists. The aftermarket has done the YZ4 a great DISSERVICE by dumping all those oversize headers on the market. All they do for most people is punch a giant hole in the torque curve around 3500 and make the transitional jetting a NIGHTMARE in exchange for a bit of overrev. What these NITWIT companies don't seem to realize is the YZ4 has a short rod by Japanese standards and extremely small valve area (25.8%) to piston area ratio for an 11,000 rpm motor. Basically what this means is they biased the breathing towards the 3000-7000 range. Listen to Doug Dubach ride one sometime and you'll hear him short shifting compared to most guys. He knows!! The little overrev you get with oversize headers is lost on an engine that isn't designed to breath up there, and it hurts the powerband in a place where it can least tolerate it unless you're a flattracker, or riding Reno to Vegas . On 94mm big bore motors the oversize pipe is less of a liability because the extra bore size increases intake velocity enough to help mute the low rpm glitch.&nbsp;&nbsp;The Big Gun and the Yosh step headers have the most potential on a stock motor. I haven't had the opportunity to test them on the bike, but the dimensions look very good in a computer simulation . The stock pipe and muffler work very well, despite what MXA, DB, and the rest of the guys looking for advertising revenue will tell you. I'm building a 441cc SuperTT motor this winter, with a heavily modified cylinder head and I'll be testing a stepped pipe I designed based on the stock pipe. I'll be comparing it to the oversize single diameter headers just for fun (it easy to get one used CHEAP). The new Big Gun pipe will probably work better than either though :


Times are changing and that half-assed "Engineering" those guys try pass off won't cut it anymore. Companies like Big Gun who actually truly engineer a product are the wave of the future.

RANT MODE OFF (for now)



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Rich Rohrich
Applied Fluid Dynamics
rrohrich@interaccess.com
www.eric-gorr.com
 
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#8
I have a few points to touch on....

1)&nbsp;&nbsp;The YZ4 is a great bike, BUT, it it very heavy.&nbsp;&nbsp;I can feel the difference anytime I'm on it, and I can really feel it if I jump on it right after I get off my RM.&nbsp;&nbsp;It seems Yamaha could do something about the weight of the bike without increasing the price too&nbsp;&nbsp;much.&nbsp;&nbsp;The first time I ever loaded Jason Clishe's 400 in my truck, I thought my nuts were going to sag to my knees.&nbsp;&nbsp;That bike is heavy!&nbsp;&nbsp;Yamaha's claimed weight is a joke of a number (238... bbwwwaaahahahahahahaha!!!).&nbsp;&nbsp;BUT, it does do most everything extremely well.&nbsp;&nbsp;Even after just a couple laps on Jason's bike, I could corner on it faster than I could on my RM.&nbsp;&nbsp;It takes a different riding style, but it corners good, flies like a rocketship, and is never searching for traction.&nbsp;&nbsp;The weigt of the bike would wear me out too quick to seriously think of racing one though.&nbsp;&nbsp;Come to think of it, it's heavy, but it also seems to carry it's weight too high for my tastes.&nbsp;&nbsp;YMMV.&nbsp;&nbsp;It also deos not want to lug down low without stalling.&nbsp;&nbsp;It seems like Yamaha would have been better off putting a little more flywheel on it, IMO.

2)&nbsp;&nbsp;We will never see another sub 200 pound 250 with a reasonable price tag, IMO.&nbsp;&nbsp;Today's riders are flying 6 times as far as the riders of the 70's.&nbsp;&nbsp;Bikes back then could be made lighter, because they were not as beefy, because they didn't have to withstand 120 foot triples and things like Larocco's Leap at Reb Bud.&nbsp;&nbsp;Bikes now are also liquid cooled, meaning more weight.&nbsp;&nbsp;We own a mid 70's Yamaha enduro, and I took at that thing and think "I wonder what would be left of it if it was ever jumped over a 120 foot triple?"&nbsp;&nbsp;Probably not much.&nbsp;&nbsp;&lt;G&gt;

3)&nbsp;&nbsp;I think as more manufacturers get involved in the 4 stroke market, you will see the weight come down, but never to a 2 stroke level.&nbsp;&nbsp;I'm excited to see what the KTM's are going to be like.&nbsp;&nbsp;As more poeple get involved, I think the envelope will be pushed, and the bikes will get better.

J&K

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J&K Racing Since 1997
Keepin' it real!
 
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#9
Well, I agree that the Yamaha is not the Holy Grail of 4 stroke technology.&nbsp;&nbsp;Hopefully the rest will improve on it and we'll have better and better bikes coming out in the future.&nbsp;&nbsp;I also agree that Yamaha screwed up by making the bike so complicated.&nbsp;&nbsp;For now I'll stick with my ATK that has a 20 year old motor with it's electric starter and weighing 300 lbs.&nbsp;&nbsp;You just can't jury rig an electronic carb with zip ties and duct tape when something goes wrong.
 

Rich Rohrich

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#10
ATK Adam wrote :
You just can't jury rig an electronic carb with zip ties and duct tape when something goes wrong.
Adam if everyone thought that way we'd all still be riding Hodaka Super Rats, and CL 350s
 

Rich Rohrich

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#11
Payday2 wrote&nbsp;&nbsp;
It also deos not want to lug down low without stalling.&nbsp;&nbsp;It seems like Yamaha would have been better off putting a little more flywheel on it, IMO.
John, my guess is Jason's bike isn't jetted right or he's using fuel that isn't cooperating. With the stock pipe it's pretty easy to lug the motor if it's setup correctly, but you're right all day lugging like woods guys do would do better with some extra flywheel weight. I really love the spin up on a SX type track so I'm happy with the way Yamaha did it.






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Rich Rohrich
Applied Fluid Dynamics
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www.eric-gorr.com
 
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#13
Rich,that's very profound.&nbsp;&nbsp;But we do have simple bikes available today that are quite a bit better than a Super Rat.

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Adam
94 ATK 605
94 ATK 406
84 YZ 490
 
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#14
But we do have simple bikes available today that are quite a bit better than a Super Rat
Like the Z50... I know, I learned on a Wombat (Combat?) and the '98 Z50 has superior power, handling, and over all comfort
. But nothing could beat that Hodaka style, no one can argue that!
 
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#15
I jsut want to comment on the Big Gun pipes. I've got an XR650L that had the stock exhaust when I got it.&nbsp;&nbsp;First I opened the airbox, rejetted and went with a Thumper racing exhaust insert. Big improvement!&nbsp;&nbsp;Then I decided I needed a better pipe and bought a Barnum pipe, with a 4 inch suptrapp silencer.&nbsp;&nbsp;This used the stock headpipes and was as dramatic an improvement as all the other mods combined. But it was loud and I didn't like the supertrapp vented exhaust gas onto my rear fender. So when I saw a used Big Gun system for sale, I jumped on it. The Big Gun pipe really woke up the big XR, now third gear wheelies are easy and I wouldn't have believed the power increase.

I've also got a Big Gun on my XR250R, but all I can judge it against is the stock pipe.&nbsp;&nbsp;Again a HUGE power increase, not to mention great sound and great looks.


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Jim Nelson - Douglass, Kansas
1989 Honda XR250R
1994 Honda XR650L
1976 Yamaha TT500C
1999 Honda Recon