Which 2T oil your old two-stroke needs: JASO FB, FC and FD explained

The short answer first. Buy a 2T oil that prints a JASO grade on the pack, ideally FC or FD, and mix it at the dose the maker states, which on Indian 2T oils is commonly 20 ml of oil per litre of petrol. A bottle that says only "2T oil" with no grade and no dosage is telling you nothing you can check.

Waxpol's Super 2T page, for example, calls for "20ml for each litre of petrol or as specified by the engine manufactures" and sells the oil in packs from 40 ml up to a 205 litre barrel. The 40 ml and 60 ml sachets exist for exactly the reason old-timers remember, one sachet to a tankful at the pump.

What FB, FC and FD actually certify

The grades come from JASO M345, the Japanese two-cycle oil classification. It was introduced in 1994 as JASO M345-93 and revised in 2004, when the old FA grade was dropped and FD was added. FC keeps the same lubricity and initial torque requirements as FB but sets far tougher limits for detergency, exhaust smoke and exhaust system blocking. FD is FC with a much higher detergency requirement again. So where a manual or a shop asks for FC, an FD oil is the safer buy, not a compromise.

Two things follow for an owner. First, detergency and blocking are the tests that matter most to a 40 year old bike, because they are about carbon on the piston crown, a fouled plug and a silencer that slowly chokes. Second, the grade is a registered claim, not marketing. The JASO Engine Oil Standards Implementation Panel publishes the current M345:2024 manual and an English edition of its Filed Two Cycle Gasoline Engine Oil List, so a brand that claims a grade should appear on that list.

You will also see API TC and ISO-L-EGD on better bottles. Motul's 510 2T, a semi-synthetic sold here, lists API TC, ISO-L-EGD and JASO FD together.

Premix or oil pump, and why it changes the answer

Before you mix anything, work out which system your machine has. Yamaha developed its Autolube pump for racing in 1961, showed it publicly at the 10th All Japan Motor Show in the autumn of 1963 and put it on sale in 1964 on the 75 cc YG1D and the 125 cc YA6. The point of it was to end hand mixing, because the rider now filled a separate oil tank and the pump metered oil to the engine.

If your bike has that oil tank and pump, your job is to keep the tank filled with the right oil and to have the pump checked. If it does not, you are mixing by hand in the fuel tank every time. The Yamaha RX 100 that most Indian riders think of here was built from November 1985 to March 1996 with a 98.2 cc air-cooled reed valve two-stroke making 11.2 hp.

Reading the limit on the bottle

Modern 2T oils state the richest mixture they are designed for. Castrol says Activ 2T is "designed for both oil injection and pre-mix systems up to 50:1" and that it meets JASO FC, with a low ash formulation to reduce pre-ignition. Fifty parts petrol to one part oil is the same thing as 20 ml per litre. Older manuals often asked for richer mixes, so if your engine has been rebuilt to original clearances, follow the engine maker's figure rather than the bottle's maximum, and never go leaner than either.

One last habit worth keeping. Mix in a clean measuring cup, not by eye, and mix in the can before it goes in the tank. Two-stroke oils are formulated to blend with petrol, but they only protect what they reach.

Sources

• Development of Autolube, a Breakthrough for 2-Stroke Engines, Yamaha Motor History
• JASO Engine Oil Standards Implementation Panel, two cycle gasoline engine oil classification page
• JASO M345, grade history and requirements
• Castrol Activ, product page including Activ 2T
• MOTUL 510 2T product page
• Waxpol Super 2T Oils JASO FC
• Yamaha RX 100