YZ250J Fuel Mix?

[Graham]

Listen to Prof Sleepy,the best engine builder around,the rest are just clowns

[davidmc]

You are on the money Sleepy,
Lot of people scratch their heads when they have problems with old Cranks,
there are a lot of factors come into it that most people are not aware of,
 and expect the same results from vintage motors as modern motors.
Haven't we been here before?

[Lozza]

Only been saying Castor/synthetics been the go for ...............nearly 10yrs However the very best and most powerful two strokes ever made Aprilia RSA 125(and ridden by the best riders) use Elf either castor/synthetic or the synthetic 987x (or something like that).

[sa63]

My modern KTM 250 exc 2t piston had worn by 0.02mm at 150 hrs, rings replaced each 50 hrs. Wear limit 0.06 mm.
Torco synthetic oil 40:1. Good enough for me!

[Brian Watson]

In an old banger air cooled 2T.. I have been using Motorex Full synth 2T at 40:1... works very well...makes plenty of power and I have only put rings in now for about 2 years..same piston..

[JohnnyO]

My 490 Maico gets a new piston about every 3 years and has never needed a big end since I built the motor 10 yrs ago..In fact in 20+ yrs of racing vmx I've never had a failed big end in any of my bikes.
Using Motul 800 @ 40:1. Works for me!

[Rossvickicampbell]

I love this debate - must be about the 6th time we have done it.  I use Silkolene Comp Pro 2 Plus - or whatever the latest name is - at 40:1 - have never had a failure and bike just being pulled down for first rings and maybe piston now after way too many reliable hours.  Used Motul at one time - same ratio as the Silkolene - and bike "smoked" very badly.

[Viper666]

My 2 bobs

I use Motil 800 at around 30:1 in EVERYTHING.

Motorbikes (Old & new), chainsaws, brushcutter, etc.

No failures.

People who try & run lean mixes (Higher ratios) in the pursuit of horsepower are just fooling themselves.

Yes the higher mix MAY result in more HP but also more wear & heat. The lower ratio is better for your engine & if the rings are a little down will actually aid in compression so it is possible to make more HP with more oil.

As long as you jet to suit. More oil actually means leaner fuel to air ratio.

Alright 3 bobs worth.

[80-85 husky]

I run motorex at 75 to 100: 1 in everything and no drama at all. I only use it as a few mates went desert running with Leisky years ago and that was what he used (100:1). 5 days straight topped out in 6th and not a drama.

ive got a 4 y/o kato 300 and a husky 400 that have both been belted and they run sweetly and cleanly. no complaints. its all about what your happy with.

I would recommend 40 - 50 to 1 using motorex full synth.

[jimg1au]

I USE 20:1 castrol m and methenol bike runs sweet and never fouls plugs.1973 cr250m dirttracker.it revs hard as well
jim

[Ted]

Make of this what you like.

2014 Port Augusta Classic Nats. Same rider. Same day. Same track. Three different bikes.

1977 RM 125 B  29.8 hp at 11,500 rpm ( dyno figures )  Completed three motos. Best lap 2:06  Maxima 927 Castor oil @ 30:1

1977 YZ 250 D  No hp figure.  Completed one moto. Seized. Big end toast. Best lap 2:12
Silkolene @ 35:1

1977 AW 440  No hp figure. Completed one moto. Seized. Best lap 2:13
Bel Ray @ 40:1

[80-85 husky]

sounds just like a trip back in time....

[mainline]

Make of this what you like.

2014 Port Augusta Classic Nats. Same rider. Same day. Same track. Three different bikes.

1977 RM 125 B  29.8 hp at 11,500 rpm ( dyno figures )  Completed three motos. Best lap 2:06  Maxima 927 Castor oil @ 30:1

1977 YZ 250 D  No hp figure.  Completed one moto. Seized. Big end toast. Best lap 2:12
Silkolene @ 35:1

1977 AW 440  No hp figure. Completed one moto. Seized. Best lap 2:13
Bel Ray @ 40:1

What condition were the engines in though Teddles? Freshly rebuilt, ring gap checked, bored with correct tolerances,  perfectly jetted etc...more than a few variables to consider.

[Ted]

No idea Paul. They were definitely being ridden quicker than they normally are.

Like I said, make of it what you wish.

Wonder why cart guys spin their engines to 20,000rpm and run 16:1. But then again what would they know

[JohnnyO]

Make of this what you like.

2014 Port Augusta Classic Nats. Same rider. Same day. Same track. Three different bikes.

1977 RM 125 B  29.8 hp at 11,500 rpm ( dyno figures )  Completed three motos. Best lap 2:06  Maxima 927 Castor oil @ 30:1

1977 YZ 250 D  No hp figure.  Completed one moto. Seized. Big end toast. Best lap 2:12
Silkolene @ 35:1

1977 AW 440  No hp figure. Completed one moto. Seized. Best lap 2:13
Bel Ray @ 40:1

The RM was set up the best, the rider loved it.
The YZ engine was tired.
The Maico was too lean.
Simple!