YZ250J Fuel Mix?

[VMXSteve]

Just brought a mint 82 YZ250J.   In the day they ran 24:1
If I use a good quality 100% synthetic modern oil, what ratio should I use with 98 fuel?

[sleepy]

This is going to be interesting, everyone seems to be an expert on fuel oil mix.
I would stick with 25:1 and use an older type oil. Some synth oils are ok it seems but stick with the Yamaha recommended mix ratio.
Have a crank here that lasted 2 races using the most commonly sold synth oil at 50:1.

[Slakewell]

Had one back in the day.

For me i just use a premium oil like Maxima and use some oil with my fuel. I dont get anal about it, just aroundist 100ml per 5 liters. If your bike blow chunks after that it will be mostly your 30 year old carby sucking air because its fu*cked/
If you dont fit a new carby your oil petrol issue is a non issue

[JohnnyO]

40:1 with a good synthetic oil like Motul 800. Don't waste your time using an outdated oil at 25:1, modern technology is a wonderful thing!

[mainline]

Castrol TTS at 32:1 (ish) in the older bikes works for me, but oil/fuel ratio opinions are like bellybuttons as alluded to previously.   

[Hoony]

use a modern oil and run it like Johnny O says at 40:1 it will stop the power valve from gumming up and siezing and giving you grief.

i used TTS for years and its shitful compared to modern oils. they burn cleaner leave less deposits.

I think KTM even recommends 50:1 with Motorex on new a 2T KTM300EXC from memory.

Let the Fun Begin.

[sleepy]

Kawasaki recomended 25:1 for their KX125 up until 08 and Motul was not on their recomended list.
The YZ125 crank I have here was using Motul 800 and the bigend is a blue mess.

[Ted]

Irrespective of what oils we may use I think that the sponsors of the 2013 Classic Nats, Lucas Oils and the sponsors of the 2014 Post Classic Nats and Conondale Classic, Maxima, should be the only ones getting a mention.

Without sponsors there are no events. Look after the people that look after you.

[JohnnyO]

Kawasaki recomended 25:1 for their KX125 up until 08 and Motul was not on their recomended list.
The YZ125 crank I have here was using Motul 800 and the bigend is a blue mess.

Ha, that ain't from using Motul 800.. The big end was obviously ready to shit itself and no particular brand of oil would've saved it.
 Just because Kawasaki and Motul aren't in bed together doesn't mean the oils no good either.
Do they recommend Motorex?  Ktm do, at a mixture of 50:1 and they sell more 2 strokes than anyone!

[Davey Crocket]

The crank in that engine was pretty fresh.....and Teds right, MAXIMA RACING OILS and LUCAS OILS are what you should be using....they support VMX, the others don't. Maxima have been the main sponsor of QVMX for 3 years now. In the USA the biggest selling oil for motorbikes is Maxima. Mitch Payton has won more championships than any other team owner and has used Maxima from day one. Also , MAXIMA 927 is a synthetic caster based oil that has that awesome smell to it. Go kart guys all use 927 and they are revving the bejesus out of them. Using good oil does cost more but it's way cheaper than an engine rebuild. I run all my bikes at 25 to 1 and have never blown or seized an engine. It's not how much oil you use that gums up parts and leaves thick carbon deposits, it's the poor quality of oil that does that. My RM125A gets a new piston every season and when I pull it down , it's as clean as a whistle. The worst carbon build up I have ever seen is from TTS......you might be riding a 1970's bike but you don't have to use 1970's technology, we have come along way since then......Go the MAXIMA or LUCAS OILS.

[foxy999]

I run MAXIMA OIL   25:1 , great stuff.... 

[oldfart]

Castrol R 30 at 20:1    and I rev the bejesus out of my motors with no failures . I had a faulty new piston that dropped a skirt when it running in recently, of which no brand of oil could of fixed.

[foxy999]

you had to with my 400 up your clacker , that kx250 was on song....  

[sleepy]

When I said use an older style of oil I should have said don't use a ester based oil. The caster synth blends have been around for years and work very well , also some of the semi-synth oil work very well but are more prone to carbon build up. An other issue is internal corrsion which is best looked after by mineral-synth oils.

I'll tell you about another failure I repaired a little while ago. A classic road race 125, turns it to around 13500 rpm and was using castrol 747. Never had a problem, switched to Rock Oil Castor Cart 100 because it was a little cheaper and I could get it for him. Never had a problem, he swapped to the top of the line ester based Rock Oil synth on well meaning advice from the wholesaler. Very next meating it failed the almost a fresh big end turning the bottom half of the rod blue and the cage and rollers just melted together.

Off went emails to RockOil in pommy and the answer come back, Ester based can only be used in engines reving to 14000 rpm but the castor based are good to around 23000 rpm. The mineral based semi's are in the middle but they don't like to talk about that.
Problem is with the rolling element bearings need to keep the rollers turning to keep the temp under control but the ester based oils are so full of aditives to reduce drag and detergents to keep everything clean that at high rpm the rollers start to skid which very quickly over heats the rollers and cage resulting in a molten mess.
The bike in question went back to the Castor Cart 100 with a new rod kit and and has not had the problem again. Castor Cart 100 is a castor synth blend which is probably similar to the Maximer 927 and others.

I have been re-building cranks for about 30 years and i always ask what oil and mix ratio have been used. I have seen a very definate coralation between mix ratio and the rate of wear as well as type of oil against failure type.

So keep using those high mix ratios (40+:1) cause it just means more work for me and other crank builders and more money for the parts sellers.

[Davey Crocket]

Well said George.