Honda Mini Four Stroke Engine

Honda Mini 4-stroke engineHonda’s GX25 and GX35 mini four-stroke engines are built to operate in any position, making them an enticing alternative to hard starting, fuel swilling two strokes. Here’s what you need to know to operate and maintain one of these unique engines, whether it’s powering a string trimmer, a tiller or a water pump.

Starting a Cold Engine

  1. Set the throttle 1/3 of the way above “Slow.” This lever will either be on the engine or the handle of the equipment you’re using.
  2. Move the choke lever, located next to the air cleaner, to the “CLOSED” position.
  3. Press the priming bulb, located next to the choke, until fuel can be seen inside the bulb.
  4. Turn the engine switch, located on the opposite side of the choke and priming bulb, to “ON.”
  5. Hold the starter grip and pull the recoil starter straight out from the opening in the flywheel cover. On tillers, the starter should be pulled straight back, toward the handle. On other engines, your left hand should be holding the starter grip, while your right hand pulls the starter toward you.

Starting a Warm Engine

On tillers and pumps, perform the following procedure before trying to restart the motor:

  1. Make sure the engine switch is in the “OFF” position.
  2. Set the choke lever to “OPEN.”
  3. Set the throttle to the “MAX” position.
  4. Pull the starter 3-5 times.

All engines can be started using the “Starting a Cold Engine” method above, but with the choke open.

Oil

These engines are able to work at any angle because they use a rotary slinger that turns the oil into a fine mist during operation, letting it lubricate in much the same way the oil/fuel mixture does in a two stroke. Because of this, changing and maintaining the oil is a little different from other small engines.

The oil should be checked when the engine is off and sitting level. Check the oil before each use. If you’re using the engine continually, check the level every 10 hours. Wipe the dipstick/filler cap clean, then insert it into the engine without screwing it in. The oil should come up to the bottom mark on the dipstick.

The oil should be changed after a month or 10 hours of use, then every 6 months or 50 hours after that. To drain the oil, simply remove the oil filler cap and tip the engine over a recycling container. Some oil will still be inside the motor, so there’s no standard amount of oil that needs to be added; start by adding 2.7 oz. (80 ml) of oil, then slowly pour in more until the oil is at the edge of the filler neck.

Honda recommends using pump engines at temperatures between 41 and 104°F (-5 to 40°C) and other engines between 23 and 104°F (-5 to 40°C.) 10W30 oil is recommended for most operating conditions, but SAE 30 can be used at temperatures above 50°F (10°C.) 5W30 can be used at temperatures below freezing.

Air Cleaner

These engines use a foam filter element. To reach the filter on tiller engines, squeeze the upper and lower tabs on the cover to lift it off. On other engines, squeeze the tabs on the top of the cover and swing it down. To clean the filter, wash it in soapy water or a non-flammable solvent. Once the filter is dry, soak it in clean engine oil and squeeze out any excess. Wipe out the inside of the air filter box before reinstalling the filter. Honda recommends cleaning the filter every three months or 25 hours.

Accessing the Engine

To get to the spark plug, spark arrester and cooling fins, remove the 5 mm bolt at the top of the engine and slide off the plastic cover. The fins should be cleaned every three months.

Spark Plug

The plug gap should be between 0.60 and 0.70 mm (0.024-0.028 inches.) When installing, always start by screwing the plug in by hand before tightening it with a plug wrench or socket to avoid cross-threading. The spark plug should be checked once a year or 100 hours of operation and should be replaced every two years or 300 hours of operation.

Spark Arrester

Depending on the model, the spark arrester can be accessed by removing a single screw on the muffler where the exhaust exits, or by removing three screws from the exhaust outlet. If the arrester is tube-shaped, it can be cleaned by squeezing and tapping it to remove the carbon deposits. All other types should be cleaned with a wire brush. The arrester needs cleaning every year or 100 hours.

Fuel Filter and Tank

The fuel filter and tank should be inspected and cleaned every year or 100 hours. To reach the fuel filter, use a hook to pull it out of the tank. If the filter or tank are dirty, clean them with a non-flammable solvent.

Getting Parts for Your GX Mini Four Stroke

Hondalawnparts.com is a certified Honda Small Engine Equipment dealer, which means we have everything for these engines from plugs to piston rings. We can ship anything you need to any address in the U.S. and Canada.

Honda GX Engine

GX100_imgmedChances are if you own any commercial-grade small engine equipment, you have at least one Honda GX Series engine. Available in horizontal and vertical shaft versions and displacements ranging from 98 to 389 cc, this series of motors can be found in just about any type of small engine equipment you can think of. Here’s what you need to know about this motor’s quirks, from starting to troubleshooting.

Controls

There are many variations on these models and individual pieces of equipment may leave controls on the engine or move them to a remote control center, typically on the device’s handle.

The main controls are located on the carburetor, which will be directly below the air cleaner housing. Some models will have a throttle lever at the very top, almost against the air cleaner housing. Next, on the carburetor body itself, there will be a choke lever. Below that, some models have a fuel valve.

For starting, the throttle should be set to 1/3 of the way from “Slow.” On models with the lever on the engine, move the lever left to open the throttle. The choke should be closed unless the engine is already warm, and the fuel valve should be open.

On electric start models, the engine is started by turning the key or switch to “Start.” After 5 seconds, if the engine hasn’t started, release the switch and wait 10 seconds to let the starter motor cool before trying again. If the engine won’t start, set the switch to “On” and use the recoil starter.

Checking the Oil and the Oil Alert System

The dipstick is built into the oil filler cap. To check the oil level correctly, the dipstick needs to be wiped off and then inserted into the engine without threading it back into the filler neck. When adding oil, the oil level should come to the edge of the filler neck.

Some models are equipped with Honda’s Oil Alert system. This will automatically shut off the engine if the oil level gets too low. If your motor stops abruptly, check the oil level to make sure this wasn’t the cause. On electric start models, there should be a light on the starter panel indicating the oil alert system has been triggered.

On motors with a reduction gear, the gear is in a separate case with its own oil supply. It has its own filler cap/dipstick and uses the same oil as the engine. The case should only be about half full of oil, which will be well below the top of the filler neck.

Spark Arrester

No matter the model, the muffler on your engine is designed to be used with a spark arrester where required by law. The arrester can be accessed by removing the muffler shield. The arrester itself will be held in the muffler by one screw. To clean the arrester, scrub off any deposits with a wire brush. If it has any splits or holes, it should be replaced.

Air Cleaner

There can be up to three types of air filters inside the air cleaner that need occasional cleaning:

Paper elements can be cleaned by knocking them against a hard surface to loosen dirt.
Foam elements should be washed with a mild detergent or non-flammable solvent. Once dry, dip the filter in clean motor oil and squeeze out any excess liquid.
Cyclones should be disassembled and wiped clean. Any dust inside the cleaner housing should also be wiped out before reassembly.

Propane (LPG) Powered Engines

If you have an LPG-powered version of the GX270 or GX390, there are a couple differences in operation.

Since LPG is a gas, there won’t be any visual signs of leaks. Instead, smell the area around the engine. If you detect any trace of LPG, have the fuel system repaired before starting the motor.

The choke lever increases vacuum to help pull gas into the combustion chamber. Once the engine is running, the engine will provide the necessary vacuum, and the choke can be opened. There’s no need to wait for the engine to warm up.

Use only SAE 30 weight oil designed for use with LPG engines, or a synthetic 5W-30 oil if using the engine below 32 degrees F (0 degrees C.) A mineral-based multi-weight oil may be fine in other GX motors, but it will damage your LPG model.

Getting Parts for Your GX Series Engineering

No matter what your Honda engine is connected to, you can get parts for it at www.hondalawnparts.com. We’re a certified dealer, covering both small engines and Honda power equipment including generators, water pumps, and mowers. Our advanced search engine can show you factory parts diagrams so you can see exactly what you’re ordering. We ship to both the U.S. and Canada.