OzVMX Forum
Marque Remarks => Yamaha => Topic started by: YUMASTEPSIDE on January 17, 2009, 03:00:22 pm
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A mate of mine just picked up what appears to be an '83 IT490 motor in an '83 IT250 frame with XT disc drake front end.Somewhere back in the dark scary recesses of my memory (what little there is left of it )there was something about inherent problems with 490 motors ????? I know there was a problem with pinging ( I can re-machine the head to fix that ) but can anyone think of other problems ???? ??? >:( :(
Roger
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I have an IT490K (1983) & have not experienced any pinging problems using BP ultimate or 100 octane, I think there were more pinging problems with the YZ490's.
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the it 490 i had last year didn,t ping, i think the it,s were a tiny bit detuned from the yz, the 82 yz i had at the same time did a little , both had wiesco,s my k yz490 fitted with a nos top end pings but it doesn,t seem to worry anything ,just gotta be aware of it , the other two k,s have larger piston clearances don,t ping and are faster , and my wr500 which is supposed to be the worst by all accounts just goes hard (has a yed barrell and wr head ) my yz 465 pings a tiny bit as well , i think the it jetting std is a little lean for sustained full open riding , none of mine have had the blend angle machined into the head , the centerport combustion chambers seem to be a little different