Why 80:1/100:1 Fuel-oil Ratio?

[irishjohn]

I am curious why the GasGas trials bikes use a reccomended 80:1/100:1 ratio when their enduro bikes use 32:1/40:1?

[benj]

probably because they rev higher and harder so require more oil.

[peterb]

Enduro and moto cross motors work harder and are used a lot more up the rev scale than trial motors over a long period of time, hence the extra oil required. I consider 80 or 100:1 too lean for trials motors and always recommend 50:1 be it synthetic or mineral oil for the 2T mix, bit old fashioned there, I like to know there is sufficient oil in the motor.

Bye, PeterB.

[hannon]

2 strokes get their cylnder lube from the oil in the gas

endruo bikes will be reved up all day attacking hills and going fast while trials bikes rev for a few seconds and are then back down in the low revs

if you run too much oil in a trials bike you will foul plugs like crazy and oil will soak your packing in your muffler and drip out the tail pipe

i have been riding trials for 20+ yrs and my dad for 35+ yrs

recently we have been running Amsoil synthetic at 100 to 1 and have had no problems and we ride nearly every sunday

because we ride at upper levels we replace our bikes about every too years but even still i rarely hear of anyone needing a rebuild due to lack of oil in the mix

[irishjohn]

30 years ago when I competed in trials, I ran a mix of 32:1 in my Sherpa T's. The reccomended ratio of 80:1/100:1 for my GasGas XTX 280 Pro, is so much leaner than what I am used to. Does the fact that it runs a plated cylinder and is water cooled enter into the equation? Am I also correct that the main bearings are not lubed by the fuel/oil mix like older 2 cycle engines?

[jse]

30 years ago when I competed in trials, I ran a mix of 32:1 in my Sherpa T's. The reccomended ratio of 80:1/100:1 for my GasGas XTX 280 Pro, is so much leaner than what I am used to. Does the fact that it runs a plated cylinder and is water cooled enter into the equation? Am I also correct that the main bearings are not lubed by the fuel/oil mix like older 2 cycle engines?

The plated cylinder, in conjunction with the liquid cooling, reduces cooling problems and local "hot spots" on the cylinder wall. When you think about it, it's amazing how well the old two-stroke cylinders worked as well as they did. Here you have an iron cylinder sleeve, pushed into an aluminum casing with fins, cut full of asymetrical holes and cooled on one side by incoming fuel/air mixture and heated on the other by hot exhaust gases, all the while having an aluminum slug (also hot on one side and cooler on the other) racing up and down inside it, first speeding up, then slowing down and stopping, reversing direction then speeding up and then slowing down and stopping, reversing direction etc. You can see how cooling problems lead to cylinder distortion, especially if you throw mud all over it.

Yes, the Pro engine has the main crank bearings lubed by the transmission fluid, part of the reason the engine can be made so narrow.

Jon

[ianp]

Reading this with interest because I've recently acquired my first trials bike a 2003 GG 250. On the tank by the filler it says 1.5% which is 65:1. I always thought it was 80 - 100:1 for trials bikes. Which is correct?

[bikespace]

I've run 80:1 synthetic on my 04 Sherco 290 for 5 years now. I think I may have the most reliable Sherco ever. Not even a set of rings yet, and runs sweet as a nut. If my bike isn't running absolutely clean as a whistle, I know there must be a bit of water in the float bowl.

[bikespace]

75:1 or thereabouts is about right for most trials bikes but as pointed out somewhere above the Pro has the main bearings lubricated by the gearbox oil and not the oil/fuel mix as all the others... that is why the quantity of oil can be cut down.

Yeah sorry, just to clarify, I was pointing out that 80:1 is easily enough oil for the modern trials bike, and you may want even less for the Gasser, not arguing that it was specifically the right amount. Clear as mud

[jse]

Yeah sorry, just to clarify, I was pointing out that 80:1 is easily enough oil for the modern trials bike, and you may want even less for the Gasser, not arguing that it was specifically the right amount. Clear as mud

80:1 seems to work fine for me also. I've run that approximate ratio for the last 13 years in my watercooled bikes and the results in performance and reduced engine wear have been satisfactory. I do, however, only mix in a one gallon U.S. container and use only fresh fuel and a gallon usually lasts the whole day. My race fuel that I use is stored in a well-sealed steel container and as soon as I get it filled I add a fuel stabilizer and so far I've never had a problem with stale fuel, which will cause hard starting and poor performance.

Jon