yz490 ?'s

[jaykup]

I haven't been able to find a whole lot of info on these bikes through the web, some, but not a lot.

From what I've gathered, is they vibrate like hell (100% agreed with that) they tend to seize up a lot, the suspension sucks, jetting them is next to impossible, and overall they were pretty much the worst bikes ever made.

Now, I've got one myself, recently running, and recently killed, and I love it to death. Yes it does vibrate like hell, and it does idle like shit. It died because my friend was going around a turn, gave it some throttle, it pulled a wheelie high enough to throw him off and the bike ended up with the throttle stuck open. After finding out that he broke his collar bone in 4 peices, and got a wicked concussion bad enough to kill him if it wasn't for his helmet, I was more worried about getting him help, than checking out the bike. A day later it still kicked over, but the compression was at 1/4 what it normally was.

When it is running, you can just TAP the throttle, and the thing just rockets out of control. Its amazingly adicting. I found out the bike I've got has a Flatside carb on it as well, Much larger than stock. The throttle responce on mine is amazing, less than 1/4 throttle will bring the front end up easily, but I dont know how most of them are.

What are your experiences on these things? What are some known problems that I missed? Any fixes for some of the problems? I've heard balencing the crank does wonders. Any aftermarket heads or anything like the banshee has? Also, what type of clutch should I use for it? I think mine is slipping a bit. I'd like something that can hold more than stock power for a long time.

[zillaguy89]

I think you said it yourself.....lots of problems, but the level of "balls to spare" exceeds the problems you put up with. haha

[Kane]

LOL,,,,,sounds like your normal 490. There used to be an awesome site called, I think, YZ490.com but it hasnt been working for a couple monthes so it's probably dead.

Mine doesnt vibrate all that bad. It's an 82 model mill mounted in an 87 T-4 frame. I have a Mikuni VM38 mounted to it. It had a flatside 35 on it that performed much the way you describe. You may be a hair lean if so. That bike becomes more predictable with a wider range throttle too, I use a 3/4.

Timing is critical on those old beasts. 3-6 degrees BTDC is premium. It'll aid starting and help against detonation. Use the highest pump gas only. Use a high quality pre-mix as well, with any machine really. Do NOT run hot plugs. Use the recommended plug or one step colder if it'll still start properly.

While you're needing the top-end worked on, send out your head to have the squishband milled. You'll run cooler and detonation will virtually be eliminated.

I like and use Barnett and EBC clutches. I've never had as good usage from the Vesrah discs. Avoid the low price crap like Tusk and Atko, while being only $35-50 they give about 2 days ride before cooking to junk. Use a high quality gear oil as well. It'll keep tranny temps lower and extend the life of your clutch. You may just need to change your oil. Try that first. As well as making sure the cable is working smoothly.

When it comes to engine mods, avoid any that increase compression. Balancing the crank is good, leave the stroke alone.

[jaykup]

wow, thanks alot Kane. I found a nice EBC clutch off bikebandit for around 110 dollars. The head work I was hopeing there was something to do about the detonation, and there is!

I'll have the timing checked as well. I run only 93 Octane with amsoil synthetic @ 50:1. The plug is stock.

What did you mean you had it mill mounted?

[Kane]

Old slang meaning engine. Mines from an 82 YZ490. What year is yours?

[jaykup]

1984 Too bad its still dum brakes

I was looking around for someone parting one out so I could do a disc conversion on it.

How does that T-4 move with that motor on there?