Fuel: 2.6 liters, filled to the brim.

Coolant: less than 425cc.

Gearbox: 350cc minimum.  A fluid change will require an extra 25cc if the clutch cover has been removed and everything is dry.  

Some sources say it is preferable to overfill to around 450cc for better cooling.  This is especially important if you ride the bike any distance at high speeds in 6th gear.  Gearboxes have been known to sieze when using only 350cc.

Premix Ratios

I suppose a few words about premix ratios would be appropriate here.  As the old saying goes, “No one ever killed a two-stroke by using too much oil.”

The TR280i Owners Manual says to use 0.9% (9cc per liter) of synthetic oil.  That works out to a premix ratio of 111:1, which is what I have been using.  It has taken me a long time to accept that such a small amount of oil is adequate for trials.  For example, in road racing, a premix ratio of 30:1 is the norm.

I do not think much oil is needed to lubricate the piston/cylinder walls.  The fact that the crank main bearings are lubricated by gearbox oil is wonderful.  But I still have a concern over the connecting rod's big-end bearing oiling.  It appears that the fuel injector sprays directly onto that area – very clever both from a lubrication standpoint and to help ensure adequate mixing of the fuel with the incoming air charge.

Another factor in my decision not to use leaner oil ratios is that my fuel contains ethanol.  Two-stroke racers using methanol-based fuels have learned the hard way that copious amounts of oil are necessary for longevity.

For the record, I use Motul 800, but think a wide variety of oils would probably be satisfactory.   If you think your bike smokes too much, do not just use less oil.  The fuel/air ratio is probably too rich.  It is also possible your engine is burning gearbox oil. 


I realize this website will be read by a worldwide audience.  The fuel where you live may have a very different composition than the fuel where I live.  Even within the United States, pump fuels can vary significantly due to local laws and by season.

Where I live, gasoline that contains 10% ethanol (E10) is the norm.  You have to go out of your way to buy fuel without ethanol.  Vehicles that lack a closed-loop feedback system (oxygen sensor) experience an “enleaning” effect when burning E10 compared with straight gasoline.  This amounts to about 3.5 percent - about 1 main-jet size.  For example, if a carburated or open-loop EFI engine operates with an air-fuel ratio of 14.6:1 on straight gasoline, it would become about 15.1:1 when burning E10.  This enleaning effect can be beneficial or harmful to performance – depending if the original jetting is rich or lean.

My original TR280i map seemed to be quite rich, so the enleaning effect was beneficial in my case.

As for the octane rating, I was quite surprised that the lowest grade of fuel works without any signs of detonation or audible knock.  Again, on a worldwide basis octane rating may be expressed differently.  Here in the US, it is expressed by the (R+M)/2 method.  That is, it is the numerical average of the Research Octane Number (RON) and the Motor Octane Number (MON).  Expressed that way, 87-octane fuel works fine for me.

Fuel Consumption

When I first got my 280, its fuel consumption was nothing short of atrocious.  At one point I ran through 2.6 liters of premix in only 55 minutes!  This was with the original 2011 ECU.  The bike did not run well, but it did run.  This illustrates how tolerant 2Ts are to rich mixtures.

After upgrading to the 2012 ECU and cleaning the fuel injector, I have been using about 1.2 liters per hour.  My 250 gets slightly better fuel economy - about a liter per hour.

Fuel consumption is highly dependent on riding conditions.  When free-riding I spend most of my time in 3rd gear (geared lower than stock) with constant clutch work.  The loop trail is often about as difficult as a Novice section.  I infrequently use 4th or 5th gear.

Engine Coolant

OSSA does not mention engine coolant (radiator fluid) other than to say it should be changed yearly.   But they also say the piston should be changed yearly(!) so I will leave that to your discretion.  I use a 50/50 mixture of distilled water and ethylene glycol.  There is no coolant recovery tank, so any excess coolant just ends up on the ground due to thermal expansion.  I  fill the radiator until the core tubes are just covered.   The pressure cap is rated at 1.2 bar (about 17.5 psi).

Pure water has the best heat transfer properties.  The more antifreeze in the cooling water, the worse the heat transfer becomes.  Of course, no antifreeze means you lose freeze, boil-over, and corrosion protection.  I have used a product called MoCool by Motul in roadracers where antifreeze is prohibited.

Gearbox / Clutch Fluid

I have used a variety of ATFs (automatic transmission fluids).   My current choice is Valvoline Dexron VI, mostly because it is a full synthetic that is readily available and inexpensive.  You will have your favorite, which will probably be just fine.

I use a synthetic ATF in the gearbox because I like how it makes the clutch operate.  But clutch feel would be less important on the Explorer than a trials bike.  It might be smarter to use a high-quality gear oil there since the gearbox is so fragile. 

Lately, I have been draining the clutch/gearbox just by tilting the bike to the right and loosening the clutch cover.  On the 2014+ bikes, removing the cover screw closest to the bash plate will allow much of the fluid to drain out.  I do this as a first step to minimize the mess.  I also inspect the drain plug magnet for metal. 

Clutch Hydraulic Fluid

I have been using Magura Blood because it is readily available in the US.  A mineral oil must be used, preferably one with a very low viscosity.  I have used a 3-weight suspension fluid in a pinch.  It seemed to work okay, but I eventually purged it, as I think some of the clutch's feel comes from the viscosity of the fluid.  Magura Blood is like water in that regard.

Do not substitute DOT3 or DOT4 brake fluid.  The seals in a mineral oil system are incompatible with the seals used for DOT brake fluid.  Although DOT brake fluid was used for some hydraulic trials clutches, the slave cylinder was mounted external to the engine.  When the slave cylinder is mounted inside the engine, there is the possibility of gearbox oil coming into contact with the slave's seals.   Hence the requirement for a mineral-based hydraulic fluid.