The YZ426 was only made, 2000, 2001, 2002. So it can only be 1 of those 3 years, and 2001's have changes in the frame from 2000, with an aluminum rear sub-frame, 2002 im not quite sure what the difference is. But look at your vin number, and find a yamaha vin decoder and you'll figure it out.
48
sorry to tell you but they don't make a 1999 yz 426..they make a yz 400 that's a 1999
The carb should fit but the jets would be wrong, I know the 426 is 2 stroke but if the 400 isn't also 2 stroke then you will have some problems also if they are not from a similar frame style then some parts might not line up or fit.
the first yz 85 was built in 1977
yz 80 B
2001-2012
2001
Look on the vin tag on the right side of the steering head tube.
To find out the year of your Yamaha YZ 80, you will need to use the VIN on the engine casing. Copy down this number and take a look at it. If the tenth character is a letter, your YZ 80 was manufactured between 1980 and 2000. If the tenth character is a number, it was manufactured between 2001 and 2009. For a more accurate year, you can call Yamaha's customer service number and give them the VIN. They will be able to decode it for you.
1982 yz 125K
no the 450 would be faster because the bore is bigger, and also the 450x is an enduro so it has longer gear ratio meaning you dont have to shift as much as the race model and you can go on roads with it.
2004