1987 YZ490 Jetting

collinsvintage
I just bought a YZ490 located in Colorado but I will be riding it in Florida (6000ft difference). I've heard the jetting on these bikes are tricky and was wondering if Ill be able to set it up with just needle/air screw adjustments. I don't want to run any risks and rather run the bike a bit rich if needed. Thanks
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Matt Fisher 3/11/2020 4:15pm
3/11/2020 4:15pm
Everything I've ever read about the Air Hammer suggests that the factory head squish band was very poorly engineered. Have it cut by someone that knows what they're doing and then go about jetting it. Otherwise you'll be chasing your own tail.
DynoDan22
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DynoDan22 3/12/2020 6:27am
3/12/2020 6:27am
+1 Matt Fisher. Reach out to Tom Morgan as I believe he knows the trick to reshaping the combustion chamber for a more efficient burn. I've seen people struggle with the 490's until finally getting the head dimensions corrected.
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Rocky739
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Rocky739 3/18/2020 7:16am
3/18/2020 7:16am
DynoDan22 wrote:
+1 Matt Fisher. Reach out to Tom Morgan as I believe he knows the trick to reshaping the combustion chamber for a more efficient burn. I've...
+1 Matt Fisher. Reach out to Tom Morgan as I believe he knows the trick to reshaping the combustion chamber for a more efficient burn. I've seen people struggle with the 490's until finally getting the head dimensions corrected.
^^ What he said. A proper set up 490 runs nice. Stock or done incorrectly, not so much. Tom does quite a few of the 490s and has the knowing of things. Fast turnaround and fair prices too.
DirtRoadmx47 3/22/2020 9:04am
3/22/2020 9:04am
See if you can find the yamaha race updates for that year. I had an 83 and it blubbered and fouled plugs every ride till i replaced the needle jet,forgot what size but it ran great after that.

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