Servicing the Subaru EX-Series


The Subaru EX-Series, also sold under the Robin and Subaru-Robin brands, has been used in several of Billy Goat’s models over the years including the current F902S Force wheeled blower. If you want to get the reliability expected from this top-rated industrial motor, you need to maintain it properly. Here’s what you need to know from pre-use checks to long-term storage.

Maintenance Schedule

Every day or 8 hours of use: Clean the engine, check the nuts and bolts for tightness and check the engine oil. On models with an oil bath air cleaner, top up the air box oil pan.

First 20 hours, then every 100 hours thereafter: Change the engine oil.

Every 50 hours: Clean the air filter.

Every 50 hours or weekly (EX13, 17, 21 and 27) or 100 hours (EX 35 and 40:) Clean the spark plug.

Every 100 hours, if equipped: Clean spark arrester.

Every 200 hours: Replace the air filter, clean the fuel cup and clean and check the spark plug gap.

Every 500 hours: Replace the spark plug.

Every year or 1,000 hours: Replace the fuel lines.

Subaru also recommends taking the engine in for professional service every 500 hours to have the carburetor cleaned and adjusted and every 1,000 hours for an overhaul.

Oil and Oil Bath Air Filters

Some models come with an oil sensor that will shut off the engine if the level is too low. Adding the oil to the crankcase will re-enable the ignition system, letting you restart the engine.

To check the oil, place the equipment on a level surface and remove the dipstick from the oil filler neck. Wipe off the dipstick and put it back into the neck without screwing it to get an accurate reading.

10W30 is recommended for most operating conditions. SAE 30 can be used for temperatures above 50°F (10°C) and 5W30 at temperatures below 25°F (-5°C.) The amount of oil your engine holds depends on the model:

EX13, 17 and 21: 0.6 quarts (0.6 liters)
EX27 1.1 quarts (1 liter)
EX35 and 40 1.2 quarts (1.2 liters)

To drain oil from the engine, remove the drain plug, located below and to the right of the filler neck.

Some versions of the EX13, 17 and 21 have an oil bath air cleaner. Add oil to the filter box up to the level marked on the side; if it’s empty, it should take about 3.5 tablespoons (55 ml.)

Spark Plug

Carbon deposits should be cleaned off of the spark plug using a plug cleaner or a wire brush. The electrode gap should be between 0.02 and 0.03 inches (0.6-0.7 mm.)

Fuel Cup

The cup is located at the base of the carburetor, directly below the air filter box. Close the fuel valve before removing. Once any collected water or dirt has been dumped out, it should be rinsed with gasoline or kerosene.

Air Filter

Oil bath air cleaners have a single foam element. Wash the filter with kerosene or diesel fuel, then saturate it with a mix of three parts kerosene or diesel fuel and one part clean engine oil. Squeeze out the filter to remove any excess fluid.

All other engines use a dual element cleaner. Wash the foam element with water and a mild detergent and let it dry before reinstalling. Do not oil the element. Tap the paper element against a hard surface to knock out any loose dirt.

Spark Arrester (EX 35 and 40)

To access the spark arrester, remove the muffler cover, which is held on by three screws near the deflector. The spark arrester is held in by a single screw next to the muffler opening. Use a wire brush to clean off any carbon deposits. If there are splits or holes in the arrester, it should be replaced.


Subaru recommends following this storage procedure if the engine won’t be used for over one month.

To drain the fuel, close the fuel petcock and remove the fuel cup. Place a suitable container below the carburetor and open the petcock. Remove the drain screw on the side of the carburetor to get the remaining fuel out of the float bowl.

Change the engine oil before storage. Remove the spark plug and pour in about a teaspoon (5 ccs) of oil into the cylinder. Slowly pull the starter handle two or three times to circulate the oil, then reinstall the plug.

Slowly pull the recoil starter until resistance is felt. This positions the valvetrain so that both valves are closed, sealing the inside of the cylinder.

Clean the engine with an oiled rag. Store the engine in a well-ventilated, low humidity area.

Getting Parts for Your Engine is a certified dealer for Billy Goat and their manufacturing partners including Subaru Industrial Power, which lets us provide the full line of OEM parts for these engines. We can ship anything you need to any address in the U.S. or Canada.

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