1986 YZ490

[Stratochiefer]

A while ago I purchased this YZ 490. The history is unknown, all I know is that it was stolen once upon a time and was reclaimed sans serial number. I have a service manual but according to it there were many different models of YZ490s with many different needle and jet combinations. Can anybody give me some advice as to how to tell the models apart from one another and which needle/jet combination works the best. I have destroyed one and a half pistons already and I am getting unbelievably frustrated. This is my third yamaha dirt bike and I know how nice these machines can be.

[Big Maico 393]

The problem with the YZ 490's is that the head is a poor design & they are very hard to jet!

You have 2 choices, one is to have the head redone by Tryce at [Only registered and activated users can see links. ]


Or have ProForm racing build you a pipe to help.

You might be able to fine some number on the engine case if they didn't file them too!

[yz490freak]

Theres a head mod you do, makes the jetting clean up in the mid with out pinging. Its a 8mm 30deg angle around the squish band, that was the problem was the squish. Let me know if you need a diagram, Ill email it to you

[Stratochiefer]

Thanks for the advice on the head reshaping. A diagram might be helpful. I am also wondering what a good starting needle setting would be for braking in a fresh set of rings if anybody has any good info. I will be looking for a new rear shock, does anybody know of a good retro fit to rid the bike of the stock junk?

[chickenrick]

i have a 86 yz490 i was woundering if you could e-mail me the specs. for the head mods.
thanks Rick

[merlyn1965]

I just bought a YZ490 1989 and I am seriously looking to find those specs. Is there a chance that you could also sent them to me too? So far I like the bike but it is a real son of a ...... to get started. When it is running it is lots of fun to scare the young guys on their 4 strokes. They do not enjoy getting passed by a 43 year old fat man on a 19 years old bike. I am trying to get the bike running as good as the YZ490 of Broc Glover was in 85. Hope you guys will be able to help me to achieve it.
PS. I put in Boyesen reeds and since then, to start the bike cold is extremely challenging...
Josh