Honda 75/90 hp Four-Stroke

First, Honda showed the visiting press the new (and very quiet) 75 and 90 hp outboards. Then the company opened the doors to the brand-new Honda Fit, a small car new for 2007. The tie-in? The Honda BF90 outboard is the identical engine as the one in the Fit automobile, with the exception of the gearing: The outboard still only sports a single gear. But who knows what the future might hold ?

Both the 75 and 90 use the same 1,590 cc (97 cubic-inch) block. Honda calls its fuel-induction system four-to-four since each block has four cylinders, each with its own carburetor. Honda believes this design provides better responsiveness than a single, large throttle body carburetor.

Anyone who’s ever had to take the cowl off while at sea will particularly appreciate that Honda mounts the alternators, ignition and other electronic components on the top of the engine. (Now if Honda would only extend the oil dipstick tube to the top so water can’t enter the tube while you check the oil offshore, it would be perfect.) Another protection-from-the-elements feature finds the starter mounted upside down in a sealed chamber.

Most outboards have the flywheel on top of the block, we suppose because back in the day, you could attach a pull cord to it and start your engine. Honda has moved the flywheel down to the bottom of the block where it lowers the center of gravity. Oh, and it calls the flywheel a “torsion dampener” now.

Interestingly, Honda employs a single overhead cam with three valves per cylinder – two intake and one exhaust – for improved torque. An engine-alarm system utilizes audible as well as visual alarms in case of engine malfunction, and the engine’s computer also automatically decreases rpm to prevent engine damage. The same computer that controls the alarms also monitors many parameters and constantly adjusts the ignition timing during start-up and throughout the entire operating range for optimum performance.

Anyone who has had his four-stroke serviced will really like Honda’s new “screw-type” valve-adjustment system. Since the valves no longer require shims and the oil filter mounts right on the engine front, routine maintenance no longer takes hours or costs a small fortune.

Of course, all of Honda’s engines have anti-corrosion systems consisting of numerous layers of paint, sacrificial anodes, waterproof connectors and stainless-steel parts wherever necessary to prevent any saltwater intrusion. The 75 and 90 also both carry an ultra-low three-star California Air Resources Board (CARB) rating.

We ran these new engines in Japan on various skiffs and flats boats and came away impressed with the torque. We had no problem getting up on plane quickly. And yes, you can expect these engines to weigh more than comparable horsepower two-strokes, but they tip the scales at about the same weight (373 pounds) as the competition’s four-strokes. The factory lists full throttle as 6,000 rpm, though both engines develop their respective horsepower ratings at 5,500 rpm. The standard gear ratio is 2.33:1.

Mounted to a 17-foot Action Craft bay skiff (910 pounds), the 90 hit a top speed of 40.2 mph using 8 gph for an amazing 5.03 mpg. Dropping the speed to 26.6 mph raised that economy to 7.6 mpg (3.5 gph). That represents an awful lot of fishing spots to visit between fill ups.

While the BF75 comes only in a 20-inch model, you can get the BF90 in either 20- or 25-inch versions. Honda makes both engines in tiller or remote-steering configurations, with a 16-ampere charging system and electric start as standard.

As you would expect from the company that pioneered the modern four-stroke outboard, the BF75 and BF90 run so quietly that at idle, you need to put your hand on it to tell if it’s running. That alone will spoil you in no time.