Mercury F50

Mercury Marine has steadily upgraded the F50 since it was first released locally in 1995. The original powerhead displaced 935cc, but the current model introduced late last year now displaces 995cc. In essence, it is a de-rated F60 and a four cylinder, four carburettor version of the brilliant F40, which has proven so popular with freshwater anglers. However, the cylinder head is still from Yamaha and the crankcase and crankshaft from Mercury, while the leg and lower unit are pure Mercury.

Although the F50 is available in both standard gear ratio and 'Bigfoot' lower unit models, the standard ratio model is the one for compact aluminium runabouts. With its 2.3:1 gear ratio gearcase from the two-stroke Merc 75/90, the Bigfoot model is better suited to houseboats and semi-displacement workboats, as it creates excessive lower unit drag when used on planing hulls.

The F50 is well-equipped for its output and has CD- ignition that electronically advances the ignition timing for both normal operation and cold start, plus engine protection features that include a rev limiter, automatic low oil pressure and engine overheat revs reduction. Cold starting is assisted by an automatic choke which eliminates the 'hit or miss' of the electrically-operated manual choke system of Honda's BF50 and provides instant turnkey starting when cold.

However, there's still the problem of the automatic choke sensor cooling faster than the powerhead when the motor is stopped for 10-15 minutes, but by insulating the sensor so that it cools at the same rate as the powerhead it will 'think' the motor is still hot and hold the choke open. Your local Mercury dealer can make this modification.

While correct carbie balance has been the bane of many four-stroke outboard owners, according to owner reports, the F50 has proven relatively troublefree. Its simpler carburettor balancing linkages mean it's easier to tune than Yamaha's F50A and holds the tune for longer.

The demo F50 started instantly, hot or cold, and warmed quickly. Provided the antiventilation plate was kept immersed, power astern was good and no cooling-water starvation occurred. But because the idle speed was set at least 200 revs too fast, no trolling speed or fuel consumption figures were recorded, yet surprisingly there wasn't much of a 'clunk' into forward or reverse despite the weight of the stainless steel prop fitted.

Mounted on a Stacer 455 Kingray runabout, which displaced 650kg including two adults, the F50 provided a good blend of performance and fuel efficiency despite spinning an 11-inch Quicksilver Vengeance prop and being way underpropped. When the throttle was opened out to fast idle, there was no hesitation in the transition from idle to main carbie jets, and the motor planed us cleanly at 22.0kmh on 3400 revs.

The best cruising revs were 4000 where the F50 averaged a quiet 28.0kmh consuming 7.4lph. Through tight figure-of-eights at these revs there was no prop ventilation, although the rapid-acting power trim was surprisingly noisy.

Over a 20cm chop the Wide Open Throttle average was 53.0kmh on 6300 revs and hitting the rev limiter. Swapping for a 12 or even 13-inch prop would have made a big difference, but at 18.0lph the fuel consumption was reasonable and the 11-inch prop would be great for carrying heavier loads or pulling a wakeboard. Noise levels at these revs were high but not intolerable.

Undercowl access is very good, including the spin-on oil filter. Recommended servicing intervals are every 100 hours or once a year (also for waterpump impeller replacement) after the first 20 hours or three months. However, I'd change the oil and filter every 50 hours or six months, whichever comes first, particularly if you do a lot of trolling in that period.

The F50 is well-designed, well-engineered and with regular maintenance should provide years of troublefree operation. It also survives well in saltwater, according to owners interviewed.

For recreational operation, the warranty is the best of all the 50hp four-strokes, as it provides two years of general coverage, three against corrosion perforation and four for selected ignition components.