The Harley-Davidson FLHT is better known as the Electra Glide Standard; it is one of world's premier touring motorcycles. In the 1990 model year, Harley's Big Twin engine was the 1340cc (80-cubic-inch) Evolution V-Twin. Changing the oil on modern Harley engines is performed in virtually the same manner on all styles, regardless of the year model and engine family. It is a fairly simple do-it-yourself task.
Start the 1990 Harley-Davidson FLHT's engine and warm it up for a few minutes. Turn it off. Place a drain pan underneath the FLHT's oil tank. Loosen the clamp on the oil tank drain hose with a screwdriver or a 1/4-inch nut driver. Drain all the old oil out of the tank. Replace the drain plug and tighten the clamp.
Move the drain pan to the front of the engine, beneath the oil filter. Loosen the old oil filter slightly, using the proper-size filter wrench. Remove the filter when the oil has finished dripping.
Prime the new filter by pouring a few ounces of fresh oil into the filter, then install it on the engine. Twist the filter snug, then twist it by hand another half-turn. Fill the oil tank to specification (see your owner's manual).
Start the engine and let it run while checking for any leaks. Wipe the engine clean with a rag and clean up any spilt oil with an oil-dry compound.
Oil tank drain hoses on most Harleys are located either at the bottom of the oil tank or somewhere near the transmission. Most modern Harley oil filters are located on the left side at the front of the engine. You can make a sluice out of scrap cardboard and use it to deflect the old oil into the drain pan when you change the filter. This helps to avoid spilling oil on the engine case.
Hand-tighten the oil filter. Do not use the filter wrench to tighten it. Buy and wear a pair of mechanic's gloves. Protect yourself from burns when working on a hot engine.