Minimum Octane req on '98 YZ250

Joined
Feb 19, 2004
Messages
2
Likes
0
#1
I haven't been on Bike in years, wanting to get back into it, so I bought a '98 YZ250. I know stuff has changed, so I'm trying to figure out the Octane requirement.

I've tried the following: searches on here, calling Eric Gorr (no answer), called Yamaha, and local dealers. The dealer says my minimum octane requrement is 93. The Clymer repair manual says 95. When I called a fuel supplier (trying to find high octane fuel in my area) he says the number in the book is probably a RON number and I could probably use 93 pump gas which is found by (R+M)/2.

So which is it (assuming no modifications from the factory, bike hasn't been raced that I can tell).

Thanks!
 

elf

Member
Joined
Jun 7, 2003
Messages
695
Likes
0
#2
93 pump gas will work just fine. My brother has a 97 and i had a 2000 both bikes ran great on premium pump gas.
 

Rcannon

Subscriber
Joined
Nov 17, 2001
Messages
1,886
Likes
0
#3
I would love to be able to find 93 at my local pump. The best I can do is 91.

I have had no trouble running this in my 97 YZ 250. Obviously, jetting has to be somewhat correct. I am also running at 4500 ft elevation.
 

Rich Rohrich

Moderator / BioHazard
Joined
Jul 27, 1999
Messages
22,725
Likes
531
Location
Chicago
#4
gearhead1 said:
When I called a fuel supplier (trying to find high octane fuel in my area) he says the number in the book is probably a RON number and I could probably use 93 pump gas which is found by (R+M)/2.
He's correct. :thumb: The usual difference between the RON & MON rating is 8 to 10 points (called the fuel's sensitivity). If you do a little simple algebra you can manipulate the pump numbers and see that the 95 RON rating will be satisfied with 93 octane pump fuel. As altitude goes up octane requirment goes down, all else being equal. So you'll usually see lower pump numbers if you buy your pump fuel at higher altitudes.