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  #16  
Old 07-05-2010, 10:44 PM
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Default 1989 YZ 490 question

Hey all,

Brand new to the forum. This is my first post. I've been digging around for a while now looking for specific info on the question I have but have had no luck. So since this is a recently active thread I thought I'd ask here and hopefully find the answer or perhaps someone can direct me to the proper thread.

I've got a 1989 YZ 490 that I bought brand new off the showroom floor. I've been riding it ever since. The bike runs flawlessly as far as I can tell (not an ace mechanic). It starts by the third kick every time no matter how long it's been sitting. I've ridden it in all kinds of settings from open desert (where I bought it) to tight and rocky Sierra Nevada trails (where I live now) and love, love, love it.

She idles well, doesn't foul plugs, and runs like a bat out of hell but does seem to be the slightest bit fat at the low end. I'm not saying it doesn't have beastly low end grunt as I've throttled my way out of more than one situation in much too high a gear but I would like to tune it more perfectly.

If she was yours and she ran really well except for the slight low end fat would there be something specific you would do? Or am I better off leaving it alone since I've gotten 20 years of awesome riding out of this bike?

Thanks!

---------- Post added at 08:44 PM ---------- Previous post was at 08:41 PM ----------

I should tell you too that it does have an FMF fatty on it but I've done no other modifications. I did put a new piston and rings in it a few years back and reupholstered the seat (ha!) but other than that she is pretty much the same bike as when I first picked it up so many years ago.
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  #17  
Old 07-07-2010, 12:07 AM
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hello, just wondering if this head mod was only for the early models or is it still required on the 1987 model?8mm seems like a lot of meat to take off....maybe my head is planed?

Edit : I just bought this bike today, with a blown top end...very glad I found this forum
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  #18  
Old 07-13-2010, 09:33 PM
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Quote:
Originally Posted by Mitchpig View Post
hello, just wondering if this head mod was only for the early models or is it still required on the 1987 model?8mm seems like a lot of meat to take off....maybe my head is planed?

Edit : I just bought this bike today, with a blown top end...very glad I found this forum
Its required on basically all the bikes, and its not 8mm deep, its 8mm wide
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  #19  
Old 07-31-2010, 02:50 PM
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Quote:
Originally Posted by yz490freak View Post
Its required on basically all the bikes, and its not 8mm deep, its 8mm wide
Thanks for the reply, I was thinking that the cut was taken off the the part of the head that seats to the head gasket.....realized my mistake, and now am getting this mod done at a machine shop for 20$. Also doing the top end and mains, and got a complete fmf exhaust to replace my stock one full of holes. I was thinking of tracking down a yz125 frame though, just wondering what years are compatible and how big of a job it is.

Mitch
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  #20  
Old 08-08-2010, 03:12 AM
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Default I am new - hello all! - YZ490(L) 1984 - Dremmel?

Has anyone carried out this mod with simple tools at home? ie a dremmel?

I am suffering all the common symptoms of the 490. Pinging, over revving on idle when hot, flat spots etc. Far from sweet and I don't have access to a lathe or precision grinder etc.

My 490 is running stock exhaust, stock round slide carb, stock reeds.

It did come with an unused FMF Fatty Gold Series pipe not fitted but it appears to be from another year, the shape is slightly wrong and the mount is in the wrong place - if someone can help identify the year of the pipe it may be useful to someone else.

Last edited by danlovett; 08-09-2010 at 09:50 AM.
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  #21  
Old 10-05-2010, 01:37 PM
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Default Yz490 mods

Does anyone out there know if the yz490 can be stroked? if so to what length, 3mil, 4mil, etc?? Trying to build a drag bike
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  #22  
Old 03-20-2011, 09:40 AM
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HI I purchased a 1990 YZ 490 i have a procircuit pipe and boysen reeds to put in it when i get the cylinder back from the machine shop but was wondering if anyone knew of someone in pa that could do the head mod for me or someone that I could send it to, to have it done.
Thank you
Dan
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  #23  
Old 03-26-2011, 07:39 AM
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The same machine shop that's doing the jug I would think can do the head mod as well
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  #24  
Old 05-05-2011, 01:51 PM
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I just recently bought a 1983 YZ 490 Roller. Also 1982 YZ 490 Frame, Shock, Swing Arm, Triple Clamps and Forks. 1982 YZ 490 Bottom End and a 1983 YZ 490 Top End.

I am going to be building a 1983 Broc Glover Replica YZ 490. (I might build a 1982 Hakan Carlqvist Replica with the 1982 YZ 490 later).

I used to own a 1987 Yamaha YZ490 back in 1990 and this is what I did to it.

Porting and Head Mod: Eric Gorr (this was the 2 best things I ever could of done to this bike). I was sponsored by DGY at the time. Eric Gorr did their motor work.

Note: I should of had him perform his Carb Slide Modification also but I didn't

2 Black Cylinder Fin Plugs on each side instead of just 1

FMF Pipe and Silencer

Noleen Revalved Rear Shock

Pro Circuit Modified Forks (Non-Cartridge)

Sidewinder Sprockets and Chain (1 Tooth More in the Rear then stock)

O'Neal Aluminum Handle Bars

I am going to pay more attention to detail this time around with my 1983 YZ 490 project, but if any of you out there want your YZ 490 to run like a champion then there is a nice run down that will get you there. The main thing is to have "ERIC GORR" Port your Cylinder and preform the Head Mod.
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  #25  
Old 08-18-2011, 11:54 AM
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Moto

Is anyone still looking at this thread??
I'm looking for some info on 465's.. I recently picked a complete 465 motor up off Kijiji for a $100 bucks, and I wanted to put it in a Yamaha Warrior I have kick'n around..

I was wondering if I could use the head off a newer 490 on it, and make enuf torque to pull that heavy old quad around? Are the crank, and rod the same on a 465 as a 490?? I'm just look'n to run pump gas, and make around 50hp..

I was also look'n for some help to jet it when I'm done putting this thing together..
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  #26  
Old 12-04-2011, 06:37 AM
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just picked up a 87 490...awesome power but the vibration is a killer...anything to smooth this beast down some??

---------- Post added at 08:37 AM ---------- Previous post was at 08:37 AM ----------

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  #27  
Old 12-04-2011, 04:35 PM
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clean lookin 490 66!! one thing you can do is get rubber mounted handle bar clamps that will work and then thats about all you can do without putting it in another frame
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