fuel/oil mixture

[Newfee]

I got a 1980 yz 250 I jusy finished rebuilding and plan on riding this year and im wondering what the proper fuel mixture would be im thinking 50:1 but i heard of 32:1 or even 20:1 so im not sure what to do.

 

[moose1]

Use 32:1 with a mineral based oil! If using a synthetic based oil follow the companies recomended mixing ratio. This is usually between 40:1 and 50:1. I have always used mineral based oil at 32:1 with no problems.

 

[gforce]

back in the day when i had my 250r racing trike...honda.. i would run 50 to 1 and only used castrol oil and it ran strong for years..

 

[dooryder]

i would run 32:1 , i ran 25:! in my old 97 kx 100 it ran rich but the engine still ran strong, reason we mixed it richer was cause at 40:1 i blew the engine so i thought it would be safer running 25:1 didnt hurt the engine

 

[Landrew]

If you jet for it you can run anywhere from 20:1 to 32:1. I wouldn't run lower that 32 to 1. The cost is not going to be much more really. Even with current synthetic premix you still need sufficient quantities of oil for lubrication. Piston to skirt, rod and crank bearings all need oil. Even though they advertise 50:1 on some bottles of synthetic I would not personally do that. Proper jetting will be the cure for excessive spooge, not reducing the oil ratio in your gas. Less oil actually richens the jetting as now you are putting more fuel through the jets. More oil will actually give a fractionally better ring seal. Saving on oil now will cost more in wear later.
Dirtrider.net has done a few proper scientific tests where this has been shown.

 

[250mark1]

i have run opti 2 at 50:1 in my last three bikes with out problems
just take the time to do your jetting
you can still ruin an engine at 20:1 if the jettings wrong
2000 cr250
1985 yz490
1993 rm250