Yamaha F115A

The carburetted four-stroke outboard is best described as the 'poor relation' when compared to its fuel-injected counterparts. Hence, engines such as the Evinrude 40-70hp range and Honda BF115/130 really do spoil you...

So when Yamaha Motor Australia released its carburetted F100A, I said I'd hold off testing it until a fuel-injected version was developed. And I'm glad I did, for Yamaha has developed an engine that compares with both its Evinrude FICHT 115 and Honda BF115 competition.

The F115A is a 'stroked' version of the F100A, but has multipoint EFI and a slightly taller gear ratio. Yet the longshaft model's weight has increased by only 14% over the F100A. It's 22% heavier than a FICHT 115 which has a 60? V-four powerhead displacing 1726cc, but 19% lighter than the inline four-cylinder 2254cc BF115. The FICHT has a gear ratio of 2:1 in longshaft and 2.25:1 in extralong forms, while the Honda has a 2:1 ratio. The Honda also has a 40 amp alternator.

The demo F115A was mounted on a Quintrex 560 Freedom Sport and was the maximum-rated power for this Millennium-hulled bowrider. Spinning a 17-inch stainless steel prop and pushing a total of (approx) 1150kg (including four adults), the F115A accelerated almost instantly to 5000rpm when the throttle was OEfloored' and achieved a clean plane on 4000rpm and 39kmh, which also was the best cruising speed.

At Wide Open Throttle (WOT) and 6000rpm, it averaged 65kmh, with an estimated fuel consumption (there was insufficient time on the test day to conduct usage trials) of 35lt/hr.

In comparison, on a 5.5m Seafarer Viking, spinning an 18-inch stainless steel Raker prop, and pushing a total of 1200kg, the extralong FICHT 115 achieved a clean plane at 3100rpm and 28.9kmh. It cruised quietly at 4000rpm and 49.9kmh and at WOT averaged 5800 and 64.4, consuming 40lt/hr. Vibration levels were comparable to the F115A.

When tested, the BF115 was mounted on a 5.5m Savage Mako SP Cuddy Cabin 11 and fitted with a 17-inch stainless steel prop. Again pushing 1200kg it planed cleanly at 3000rpm and 25.6kmh and cruised very quietly at 4000 and 48.2. At WOT it averaged 5200rpm and 64.4kmh, consuming 36lt/hr. Across the entire rev range its twin counter-rotating balance shafts made it significantly smoother-running than the F115A.

The F115A also loses out to the BF115 for a low trolling speed and clunk-free shifting. At 750rpm it's 100 higher than the Honda, and no idle compensator (which maintains the same revs in or out of gear) appeared to be fitted to the Yamaha. This difference in revs might not seem much, but in marina confines the Honda moves at 5.9kmh compared to 6.3 for the Yammie.

Servicing the F115A appears straightforward and, though powerhead components are tightly packed in under the upper cowl, the spin-on oil filter is easily replaced. A nice touch is the direct-acting camshaft lobes which eliminate the short rocker arms used in the BF115.

Recommended servicing intervals are every 50 operating hours or six months for the first two years after the 10-hour service. This is followed by every 100 hours or once a year from the third year onwards (including waterpump impeller replacement), though I'd change the engine oil and filter every six months regardless of how few hours are clocked up. This works out to about $40 for the oil and filter.

The demo F115A was perfectly matched to the 560 Freedom Sport, and I believe that the engine is probably better suited to big aluminium runabouts than comparable fibreglass hulls. (Ed: Note, however, the F115A has attracted a following in offshore circles in twin-rig applications.)

Like its Honda competition it starts instantly hot or cold and the demo engine refused to emit any oil smoke. For boaters who fish freshwater as well as salt, in my opinion it's a better choice than my all-round favourite engine in this power range the FICHT 115.