1984 yz490

[volvo142]

Hello:ride: .can anybody help me with a little problem.can anybody tell me how/where i can get my top end ported to avoid "pinging" or detionation i the top end?? drawings or pictures where you machine them and how much you take off. i have 1 yz490 84, 1 yz490 85,1yz490 87 and 1 1993 wr500.can somebody help me??? best regards from Ole Ivar NORWAY.?

[doodman]

I think that the correct mod is to mill the head a bit to prevent pinging.

Good luck.

[volvo142]

yes i think so,but how much??

[no air charlie]

If I remember right, Race Tech use to specialize in milling the heads of 490s. You could give them a call. I don't know if they will give you their specs but they might be able to mill them for you.

They also sold a linkage shifter for the 490. It improved the "notchy" shifting these bikes were notorius for.

[volvo142]

okay.thanks for the infomation:ride: .butt i will try and do it my self.thats way i need to know the exsakt information:smirk:

[ghrocketman]

Instead of the head mod you could just run some decent gasoline like mixing AV100LL aviation gasoline or 110 octane Racing Gasoline 50/50 with pump premium.

[volvo142]

ok.but that will be very expensive here in norway...but i can mod the top if i can see some drawings of how they do it:ride:

[volvo142]

somebody told me that there is drawings of how and where to mill the the top in this forum,but i cant find it:thinking: .thoes anybody know were it is???

[GlennF]

Check this thread: https://www.thumpertalk.com/forum/showthread.php?t=761919

[crawdad]

Call Eric Gorr at Forward Motion and Let him reshape the head dome and run a NGK B9ES plug. These are the best starting places. I have a 84 IT490 and these mods help calm it down. Then you can probably start on the jetting issues that are born into a big 490 . Good luck.

[volvo142]

there it is THANK YOU:ride: . NOW I CAN START MILLING ?