YZ 490 Jug info please

[silverfox]

Bought 82J model one a while back, and trying to get it to run right. Played with the jetting but still won't rev out. Checking around the bike to day I notice on the barrel it has 4V600 465cc. Now the guy told me it had a different barrel on it, Now the engine and frame numbers match as in up 5x6  and matching numbers. So I'm guessing this is why I am having jetting woes. Big start well just won't rev like it's starving. Float level is ok, carb is clean. Had a 330 main which seems small to me. Thinking I need around a 360 main. Tried a 440 but no difference. Are the jugs that much different? Will an 83 jug and head work? Need to try and track down a jug and head for it. so if you know of any let me know. Thanks

[tony27]

You won't want to hear this but 4V6 is IT465

[mainline]

isn't fitting a 465 (YZ) cylinder one of the fixes people recommend for the 490's detonation issues?

[silverfox]

You won't want to hear this but 4V6 is IT465

Yea, That is what I was thinking it was. Any idea what code should be on an 82, 83, YZ 490 jug?

[tony27]

Think 82 is 5X600, 83 is 23X

[Iain Cameron]

4v6 is a 81 - 82 IT 465 . Iain

[silverfox]

Think 82 is 5X600, 83 is 23X

That would make sense as the frame and engine number start with 5X6

[crossedup2]

Hi Silverfox.
All the information you will ever need is in the site below.
http://advrider.com/forums/showthread.php?t=772033&page=12

Lots of info and does get side tracked but all good info. You just have to go through the 22 pages and find the section your after.
Peter B

[silverfox]

Is there much difference in porting between an 83 it 490 jug and an 82 YZ jug? Have a line on one and thinking the 5 speed box would be cool as well. Prefer a YZ jug but you get what you can. Would it go much harder that the it465 jug that's on it?? Thanks cause I know nothing about Yamies!!!

[yamaico]

Is there much difference in porting between an 83 it 490 jug and an 82 YZ jug? Have a line on one and thinking the 5 speed box would be cool as well. Prefer a YZ jug but you get what you can. Would it go much harder that the it465 jug that's on it?? Thanks cause I know nothing about Yamies!!!

OK silverfox, enough of the jug already. OZVMX (Australian Vintage Motocross). It's a cylinder or a barrel
Don't even think about asking for a fender...

[silverfox]

Is there much difference in porting between an 83 it 490 jug and an 82 YZ jug? Have a line on one and thinking the 5 speed box would be cool as well. Prefer a YZ jug but you get what you can. Would it go much harder that the it465 jug that's on it?? Thanks cause I know nothing about Yamies!!!

OK silverfox, enough of the jug already. OZVMX (Australian Vintage Motocross). It's a cylinder or a barrel
Don't even think about asking for a fender...

LOL. I'm just slack at writing long words!!!!!

[silverfox]

So I have found an 83 CYLINDER casting 23x00. Supposed to be ready to go. Would that be a good choice to replace the IT,  CYLINDER that is on it? Cannot find an 82 YZ one  for  a resonable price!! Opinions please??

[head]

83 YZ cylinder will be centre exhaust port and 82 YZ is angled to the side exhaust. Different frames are used. IT's are all side port exhaust.

[vandy010]

83 YZ cylinder will be centre exhaust port and 82 YZ is angled to the side exhaust. Different frames are used. IT's are all side port exhaust.

Incirrect...
82/83 are sideport
Its the 84 onwards that went to centreport...

[head]

OK, only a year out.