YZ250J Fuel Mix?

[Ted]

Sold a 81 YZ125 H to a fast club member at start of the year. I supplied the fuel and oil Maxima 927 @ 30:1 for it the whole year. No problems. End of year he pays me for it and uses his own mix. Silkolene @ 35:1. It seizes. Just another coincidence I suppose.

[mainline]

I'm sure there are good and not-so-good oils Ted, just pointing out that all the other components/tuning that go into a sweet running engine play a big part. Plus having a rider that's revving the ring out of it compared to normal use


I spent a while playing around with jetting on my GasGas ec200 and thinking it was close but not quite right.  Ended up taking a step back, putting new rings in, adjusting the squish measurement and the jetting i had settled on was perfect.

[Ted]

So how do you explain when this guy races it all year on 927 and then first time he puts Silkolene at 35:1 it shits itself. Don't give me " It's tired "

A 250 and a 440 being circulated at 6 and 7 seconds a lap slower than a 125 are hardly revving the ring out of it. The only thing that was revving it ring off was the 125.

[mainline]

Dunno Ted, maybe aliens took it away and probed it in between fuel/oil mix changes

[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

Many bikes & 20 yrs of racing
NO seizures or blowups to report.
Plenty of trophies
Motul @ 40:1

[Ted]

That's good. I am only taking the advice of Nick Dole and Ross McWatters.

[Nathan S]

Something a wise old man once pointed out to me, was that the arguments for lean oil:fuel ratios are about cost, smoke and emissions. They never mention power, longevity or reliability.

KTM recommends 60:1 or some-such nonsense, and you hear plenty of stories along the lines of "my trail ridden KTM is rooted after 700km"... I've seen a Beta run at 60:1 be trashed after 800km. My own Beta with double the hours is like new after 1400km - always run at 35:1...

[JohnnyO]

That's good. I am only taking the advice of Nick Dole and Ross McWatters.

Ross who? Haha
Whatever works for you Ted..
I run that combo cos it works for me

[oldfart]

Teddles ... Suzuki's they are built to last and are bloody bullet proof. I'll vouch for that.
And of course it would be doing better lap time's, because it had the factory option swing arm fitted.
 
 The Suzuki has been set up on a Dyno to extract the best results  and would of been  and turned to perfection  I take it the motor was newish with a bit of port
 If the Yz and Aw had the same amount of Dyno time spent on them,  they would of been tuned to perfection also.  ie plug readings would of showed what's going on.

 
 

[Ted]

No plug readings were done on dyno. After one run they said it is too rich. Dropped one jet size and instantly one more hp. Was asked how good I am at reading plugs and jetting at the track and was decided to leave as is. Still a bit rich. Ross said there is still more power to be attained through jetting but because Nick or himself weren't to be there they let it be. These two blokes have forgotten more about the ways to get reliable performance out of these old bikes than most blokes know. When either of them give advice I sure as shit listen.

You want a performance tuning tip Stewy, smash a couple of fins off your Suzuki head

[oldfart]

Nah .... just get fit and loose a couple Kg and that should be equal to 5hp gain 

[Davey Crocket]

How many pre78 125's have nearly 30 HP?.....they only had about 21 std......geez you must have some good advice how to extract that many needies Ted .....Ross McWatters, Nick Dole and George McKenzie would know more about engines than anyone else on here, the fact that some people have run really lean oil ratios and got away with it for years tells me that they are not revving the engine very hard for very long [1st gear in the pits maybe ], put a "PRO " on it and see how long it lasts.....1 lap?...maybe 2.....I put Kirk Hutton on 2 of my 125's 2 years ago at the Conondale Classic, he smoked everyone naturally...[YZ125A and RM125A]....you could not touch the engines or exhausts for about half an hour after the races they where that hot.....there still running today. Most people think they are riding fast but in reality are just wobblers......I have been out of action for about 15 months or so but ride 3 or 4 bikes at every meeting [average 17 per year]...year in, year out, there wouldn't be to many on here that ride the same bikes that many times per year without issues [admittedly I'm a wobbler but do hold the throttle wide open on occasion].....but hey, if it works for you then keep doing it.

Oldfart, you know that ain't going to happen

[Sweep Rider]

My semi-educated 2 cents worth..
I remember reading an article some time back where they Dyno'd the same VMX bike using different fuel mixes.
The 20:1 gave the highest HP reading all other things being equal.
You have to remember that the higher oil content dissipates more heat as well as lubricating everything.
Cooler running and good lubrication..... sounds good to me.

[Tomas]

http://www.bridgestonemotorcycle.com/documents/oilpremix6.pdf

[80-85 husky]

ive never heard of an engine seizure due to oil issues only ever fuel air issues. failed seals, cracked intake manifolds. run no oil and the motor is totalled no doubt about that. all these stories of it only did x hours and seized or was knackered is always due to a mechanical issue...poor airfilter fitment for 1 dusty ride can junk a bike and the owner never even notices he fitted it wrong until the bike is not going as good and then he strips it and finds its worn out...blame the oil.

change of oil could affect a crankcase seal and make it suck air, lots of mechanical things can go wrong in a performance two stroke but as long as there is some oil in the mix at a ratio thick enough to cover the bearings and dissipate heat there is usually no probs. the trick is assessing the oil and running at the appropriate mix for the oil.

ive held the husky wfo in the deep wet gluggy sand at Hopetoun for several kms in top gear for 3 long laps. no dramas at 75 to 1. If anything is gunna destroy a 2/ that will!

I wouldnt use that mix with any other brand than motorex as I got it from the horses mouth. if ktm recommend 60:1, they are being conservative and the inside run is 100:1 and well tested. im happy to use it. I dont recommend anyone else go to these extremes. im just saying there are other options than a cloud of smoke that makes a cfa volunteer nervous....