Yes the YZ490 has some vibration. A lot more than my YZ465. But I was told it could be reduced a lot by having the motor balanced. I'll see how the head mod and porting effects it first. Maybe I better not install the aluminum handle bars.
I rode an 82 YZ490 for years as an all around bike...tight trail, open sand, hills, dales, tracks, jumps, occasional paved road speed runs. Owned it from 1984 to 1995...so lots of years riding it. Most of the responses are correct. My friends nicnamed it "the school bus" because it was long and yellow. Mine had a few modifcations: Works GP modified fork and rear shock and had some head and carb work done. Now for specifics...I don't know/can't remember but it had a sweet ride. For jumping it was awesome...so long it was very stable in the air. It took a little muscle to move it around, but it flew nice and landed better than any bike I ever owned (I credit the reworked suspension). The front brake is a dual leading shoe, works pretty darn well...as much power as a disk but it will fade under heavy use. I couldn't push it that hard for too long. If you get the engine to run right, it is a beast. It never had the power of the KX or even the CR since they were both water cooled. But I would swear on a bible it would crack a ton on pavement (100 mph). In a full on drag on paved road every 250 and big bore would get the jump on me (stupid 4 speed), but by the time I was in 3rd I could match or exceed every other bikes top speed, then you shift into 4th and it was like the millenium falcon. Everyone who tried it said the same thing...it is brutally fast and never ever quit gaining speed. Unless you ride a ton (which I did for years), it will beat you to death on tight trails. The long chassis makes it more work in the tight stuff, and the power just wears you out. Three hours is all I could do at speed on it before I had to dial back just to survive. It really took a toll on your arms. If all you are going to do is trail ride it, gear it down so you can use a lot of 3rd. When we road, I used second almost exclusively. Second could bring you off the line quickly, yet had a lot of legs to it. First is nothing but wheelspin, so used only for puting around at slow speeds. I ran a Terra Flex 6.00 on it, then when is became too expensive, I would find the biggest knobby I could (5.60) and just be ready to change them a lot. I really miss mine. I think it was the best pure dirtbike i have ever owned. Granted, I owned it way too long and thus it has held a place of favor for me. Oh yeah...forgot...have fun starting it! Though mine ran clean, no pinging and could run the same plug for a season...5 kicks warm...a dozen or so cold. They better be strong kicks or you will pay for it. I learned early to stop on top of hills or mounds...the less kicking the better. Kenny
look like the standard Answer Products replacment silencer. Be careful, they fold like a cheap knife if you loop it out. Really the only game in town though. Yeah...I replaced a few.
Thanks Kenny. Lots of good info. I was told by the previous owner of this bike , that it would hit over 100 mph also. He said he passed an XR650 with a speedo that was reading 95mph, and he thought he was doing about 10mph faster than the XR. So yes, I'll be gearing it down. I've got the starting routine down pretty good. Once I get fuel down to the motor, it's 2 to 4 kicks, cold. And yes good full solid kicks, right from TDC or your wasting your time. Hot, it might start on the first kick if I get it right. And I can push start the beast, if I forget my MX boots. So far I've been told, that getting the head and ports done right well make it even easier to start. And that's worth a lot. Plus I have a 16 oz Stealthy flywheel weight I want to try. Along with smoothing out the midrange hit, the extra inertia might even help the motor start.
The flywheels on the 465/490 are big heavy muthas. Get the port/headwork done before you try the flywheel weight.
There's no reason to add flywheel weight to an open classer. Instead of "smoothing out" an open classer to ride woods and trails, I'd recommend changing your riding style. An open class 2-stroke will out-torque almost any 4-stroke on the low end, especially when you get down to the stall threshold. A big 2-stroke will pull down to like 7 rpm before stalling. There's no need to try to stay on the pipe when the going gets tight; just shift up a gear and "torque surf." The big engine inertia and torque these bikes have contribute to one of their greatest strengths: versatility. The chassis on your '82 favors stability in a big way. That'll make you work harder on the tightest trails, but it will reward you elsewhere, especially for more relaxed (like 7/10s pace) all-day trailriding. One thing that's key on a big-bore 2-stroke is dialing in the idle. If you have the idle stop screw set too high, a big-bore won't "shut down" the instant you close the throttle. Sometimes you get one or two unwelcome power pulses when coming into a corner. Take the time to set the idle air screw properly, and then dial the idle stop screw down to as low of idle speed as possible. You don't want a bike that will sit and idle on the stand all day. You want just enough idle time to put a glove on between throttle blips, and that's it. Does your '82 have the YEIS? That may help too. A close friend of mine has had an '83 YZ490 for the last dozen years or more. I've had plenty of seat time on it myself over the years on all kinds of woods trails (tight & gnarly, wide open & fast, sandy, whooped out, etc.), and also in sand, mud, snow, and on the ice. I myself have had a '94 KTM 440 EXC for the last half dozen or so years. We also have an '89 KDX200 as a spare bike. Both of us are used to riding open classers, and the KDX isn't any easier or faster for us on any terrain. If you fight an open classer it will beat you up, but it also will let you be lazy in a way you can't do on smaller bikes. I came up on '70s dirt bikes, DT's and such, a '79 YZ125, etc. The bikes from that era encouraged what used to be called a "European" riding style: feet up, smooth cornering, etc. (vs. the MX style of foot down, squared off corners, etc.). The "European" riding style is much better suited to big bore 2-strokes. Modern dirt bikes are all built for the MX riding style (even non-MX bikes).
i haven't seen it put that way in quite a while; the "European" riding style. such a great way of explaining the general difference between the old and new era of bikes. moderns sure are quick and easily flick-able, but i just don't enjoy them the same as the bikes i grew up with. i remember my old YZ490, climing a hill just above idle with no clutch work... the same hill that i had to feather the clutch and work the throttle on my XR600... or hit wide open and try not to die on my at the time brand new CR-F. kinda wish i didn't read this and the other 490 thread that's active here right now... i have enough bikes, but have found myself searching craigslist for a 490 to replace the one i sold years ago.
Thanks. I haven't had the YZ490 in the woods yet. But I have rode the YZ465 in the woods. The 490 feels like it has more low end torque that the 465, and the 465 seem to get on the pipe quicker. So the 490 powerband may be easier to ride in the woods. Even so, I have noticed this with the YZ465, It has a lot of torque even before it gets on the pipe. Even there, it has enough torque to pull the front end off the ground. I've almost flipped it going up hills, in the below the powerband range. Both bikes well idle down pretty low, But I think it could be smoother. I'm hoping the head and port work well help. I've been told that a Honda CR500 carburetor works better than the VM38, on the YZ490. I have PJ38 from a 89CR500, I'll try it once I get everything else sorted out. I don't have the YEIS on the 490. The 490 intake was cracked and I'm using a YZ465 intake. I could only find new aftermarket 82YZ490 intakes, and I don't know how well they fit/work.
I'm partial to Kehin PWK's. Mikuni VM's are the default choice on anything prior to the late-'80s. They're easy to tune and run pretty well. My cousin's '91 CR125 has a Kehin PJ on it. I haven't liked that carb. There's nothing really wrong with it, it just doesn't seem very precise. Among the guys I ride with most often, we've got 3 PWK's. They're not much harder to tune than a VM (I've even dialed in needle tapers and diameters on my 440), but they meter so much more precisely. I'd love to try the Air Striker version. Seems ideal for the low-throttle modulating you do on a big bore in the woods and on the trails. Bottom line, if I were in your shoes I would stick with a VM, but if swapping carbs, I'd only go with a PWK. If the bike already has the stock VM, might as well run it for a while and see what you think. I don't think the PJ is an upgrade. The 490 should be an absolute tractor in the woods. (I wish I could say I've ridden a 465 for comparison!) My buddy usually runs his quite rich, and doesn't mess with jetting much. I'd be chasing jetting all the time if I owned his bike, but I like crisp jetting. I've bugged him for years about trying the head mod everybody raves about, he hasn't given in yet. After rebuilding the lower end and getting his bike dialed in (it was a mess when he bought it), he got eight solid years of use out of it without ever going into the jug. He ran it until the piston slap got really bad, and it turned out he had wore through the first overbore, and right up to the second. I once looped my buddy's 490 on a hill climb. It was all sand and I picked a bad line and didn't carry enough momentum up the hill. The 490 just tractored along at fairly low RPM in whatever gear I was in, all the way to the top. What I didn't know is that I was carrying the front wheel in the air the whole way up. When I reached the top, the front wheel skipped off the sod cornice at the top of the hill, and the bike just rotated around the rear wheel. At least it was sand and the hill was steep enough to make it easy to get out of the bike's way! How about some pictures? Tight woods, new trail; had to wag the bars around these little trees to get through. Sandy hill climb. Out on the ice with 1200 gold ice screws. Crossing a bog after days of heavy rains. Starting a run through more mud. My own 440 in the mud.
Cool Pictures. Yes. I'm going to try jetting the VM in a little better. It's good enough to ride and starts good. I've found so far, that if I get the low to midrange perfect the top end suffers, and if I get the mid range to top end perfect, the lower throttle settings suffer. Right now I've got it to where it just runs good, but not perfect everywhere. Yes it would be interesting to try a PWK carburetor. I couldn't find any PWK jetting info for a YZ490 though. Maybe one jetted for a CR500, would be close enough to start.
I know it's apples vs oranges but my 84 CR500 (air cooled) suffered from pretty much the same motor issues that plague the 490's. Between the impossible jetting (can you say ping king?!) and light switch power band it was very hard to work with on the trail. After the PWK carb and Eric Gorr head/port work it is a whole different bike. Crisp, smooth and predictable power from bottom to top. More-usable-power overall and no more pinging I honestly cannot recommend those two mods enough. As for jetting the pilot, main and fuel screw are pretty easy to dial in. The needle on the other hand is going to require some homework. For me it was lots of trial and error and staring at needle charts and my notes but I finally nailed it. Sudco's needle chart helps a lot I would try to get one with a taper(s) close to your stock needle and go from there. Hope this helps, Andrew
I wonder what exactly are the mods to head and porting, which transform an open class MX bike into a usable woods machine?
Thanks. It helps a lot. The 490 is still running, so I need the extra motivation to pull it apart and fix it right. What size PWK did you use? Did you get a new one, or a used one from another machine?
My PWK came from a late model KX500 which I scored locally for $25. They're all over eBay for fairly cheap as well. I thought well the KX was a 500 so the jetting should be close so I'll start there----wrong---not even in the ball park Again I would use a Mikuni chart and compare the needle you're running now to a Keihin chart and see if you can find one that is close or the same as what you have and go from there. Because it's uncharted water and every carb delivers fuel differently there's a good chance it won't be exactly what you need but I think it should get you a nice starting point. Order a couple clips as well they're so easy to loose when you're pulling the needle out multiple times. Anyway the later KX500's used a 39mm PWK. Many bikes used or still use 38-39mm PWK's and PWK air striker carbs. Look for the "D" shaped slide. A lot of them had electronically actuated 'power jets' if I'm not mistaken you can just leave those unplugged. You can't beat JD if you want a brand new one. http://www.jdjetting.com/xcart/product.php?productid=60&cat=0&page=1&featured Here's a nice schematic showing the dimensions of the PWK. http://www.sudco.com/Diagrams323728/exppwk.gif
Not got a clue.......................but would have thought anyone who has had the mods carried out would know exactly whats been done?
I haven't had anything done to the YZ490 yet, But I did a lot of checking into it. Even Yamaha put out a wrench report to correct the cylinder head and porting on the 1982 YZ490. I'm not an expert, But from what I understand cylinder head shape needs to be correct to keep the piston from over heating. Once that's done, you can get the jetting dialed in. I have an old spare YZ490 cylinder. The port casting is so rough and irregular, that I think any kind of clean up, would be a worthwhile improvement. The YZ490 already has a ton of low end torque. So I'm real interested in seeing how the porting works out.
Here's the easy way. Machine the cylinder base -.75MM. Widen exhaust (do not raise)port keeping in mind the intended use. Open/widen/lower the boost port W/O changing height. Clean the transfers up and correct cylinder entrance angles if needed. Open intake to facilitate flow because that won't change timing due to the reed controlling it. Gore makes a Boyesen Port in his 465 cylinder but I don't see the gain being worth the effort. But he has been doing this longer than I. Correct the head for compression,MSV and clearance again keeping in mind usage. Keep the stock carb 'cause a 38MM is small for a 465/490 and suits low-mid range power. If you want to make the most of the new port timing a couple pipe mods and tuning ignition timing would finish the job. All rather elementary if you know anything about smokers. Perhaps turning off the computer,purchasing a motorcycle and riding it would lead you down the path of modifying for performance instead of just buying new. Then again maybe not. Too many good motorcycles rot behind barns and garages because of that attitude. What say you now?