Yz490

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#1
The bike I have been riding for the last two years is a Yamaha IT465 (81 model). I just bought an 82 YZ490, but it needs work before its rideable.What are some of the significant differences in the way the engine delivers power? I may put the IT's 5 speed tranny with the 490's top end, or just swap in the whole 465 motor/tranny assembly. I'm building a desert racer, i ride at 7000-9000 ft elevation, I weigh 190 lbs. I have NO experience with the big 490 YZ motors, but I sure do like the stump pulling 465 IT motor. Anybody have first hand experience with both of these bikes? id really appreciate some advice.
 

jmics19067

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#2
I have no experience riding either one yet but I have bought a crap load of junk parts to build a big bore yamaha for a project. If you want the 490's displacement all you have to do is just put the 490's jug and piston on the 465 to get a bigger engine 5 speed.

the only apparent difference between the two is the cylinder liner< 2 mm difference in bore size> and the four speed transmision. From what I understand<read in old magazine product tests> the 465 is a good engine while the 490 suffers from vibration<slap a bigger heavier piston in> and pinging/jetting problems< it looks like yamaha only cut the head bigger to match the head gasket without reshaping the squish angle for the bigger displacement/different pipe configuration>. Then add a boost bottle to try and clean up any sloppy compromises in design.
 

Studboy

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#3
From what I understand you may be better off with the IT motor than the DREADED YZ490!!! (Rick Sieman's favorite bike!!! LOL.) :debil:
 

jboomer

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#4
Yeah, I was gonna mention SuperChunky. Visit offroad.com/dirtbike if you want to hear the "experts" opinion on that bike.
 

Rcannon

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#6
I think the IT 465 is much better than the YZ 490. The close ratio 4 speed in the 490 eats it.

I had a 82 YZ 490 this was the J model with goofy rear suspension. I hope this illustrates how badly I hated the bike.

Fast foreward 15 years. I am sitting in the local Yamaha shop buying a 97 YZ 250. As the deal is being finalized, he writes the model number down. It said "YZ 250 J1" I called the deal off. The "J" in the model number reminded me too much of 82. The dealer dropped another 200.00 off of the price and I bought the 250.

The IT 465 engine was good. Something got screwed up when it went to 487 cc's. The 490 vibrated and was impossible to jet. It had no torque. The powerband was as short as a CR 80.

Super Hunky actually published some of my comments on the YZ 490. I told him it shook so bad it gave me hemroids. It was a joke, but he liked it.
 
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#7
i seems like your 490 was not tuned right , because my 84 490 has monster tourq and mad power band pulling wheelies in all 4 gears never falls on its noesits my yfz450 eater all day long , but also i have it bored to a 500 and head porting with a 44mm carb and it run on 40% 110 and 60%92 and a couple of drops of the special stuff
 

Rcannon

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#9
thumpertt600 said:
i seems like your 490 was not tuned right , because my 84 490 has monster tourq and mad power band pulling wheelies in all 4 gears never falls on its noesits my yfz450 eater all day long , but also i have it bored to a 500 and head porting with a 44mm carb and it run on 40% 110 and 60%92 and a couple of drops of the special stuff
It is possible that you stumbeled on to a set up that works for a YZ 490. I never did. The 84 at least had a working rear suspension. Search for the photo of an 82 yz 490 and you will see what I am talking about. The rear suspension is screwy. I had Utah's top mechanics work on the bike. My bike was tuned as well as any of the local pro's bikes were.

The 82 YZ 490 was on of the ten worst motorcycles ever built. Just because a person owns one that works, does not make it right.

The bikes nowdays can be bought and ridden as is. That is not the case with the 490.

I ma glad you like yours and hope it continues to work for you. I believe a CR 480 would make a better old time project bike.
 
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#10
the rear set up on my 490 sucks to 86 and on had a much beter set up that is the only thing i dont like about my 490. but wen i pull my bike on the beach at pismo and fire it up people jump and look , saying what the f### is that rumble coming from and everyone always come to check it and always ask what kind of bike is that , and i say yz490 and they wow that thing sounds mean, the only bike i know of that can beat me at pismo in hillclimb is a fully mod kx500 that will be my next bike
 
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#11
YZ490!!!

RUN,.....RUN FAR AWAY.....DON'T LOOK BACK!!!!

In seriousness though most open bikes of that era were pretty bad (except maybe Maico 490s or Honda Cr 480s) but the YZ was BAD vibrating, pinging (how could it be rich and lean at the same time?) no low end for an open bike, even with the head mods this bike would defy all tuning logic, add to that a four speed tranny and a frame and forks that would flex what felt like in half you have a very scary ride. ride one today and you will greatly appreciate where dirt bike design has come in the last 20+ years. If you really want a good '82 model bike try one mentioned above or an RM 250 these bikes were pretty good back then. This is just my experience take it for what it's worth as everyones got one.

jeffro :blah:
 
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#12
i seems like you had a ****ty 490 but also i ride a harley to , so the vibration doesnt mean crap to me the way i look at it it just takes more skill and balls to ride a 490, and another a all older rm,s had the crummy tranny in them blow out 2nd gear everytime i use to have one the bike wasnt worth a **** i gave that thing away big money pit
 

Rcannon

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#13
Your right. My 490 was bad! Still it was riding. I would not trade that for nothing. I was always angry because I traded away a good bike to get the YZ. The KDX 175 I had was a decent machine.
 
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#14
Hey there thumpertt600. I just finished rebuilding an '82 490 with .020 bored over cylinder/wiseco piston. What jetting would you recommed for this bike for improvements? It's got a DG pipe/silencer that I just repacked and It's still got the stock jetting. But, I can tell it could use some tweaking on the carb. Thanks, Kevin
 
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#15
Man.....I got to ride the YZ490 once...I'm not for sure if it was an 82' but from the way it looked it probably was...

It was strong when the powerband hit but it was the worst bike I've ever ridden...It was horrible to just ride in a straight line...It vibrated real bad and it had no low end, it hit hard higher in the rpm range than a 500 should...It was horrible.