Yamaha’s New Generation 25hp Four Strokes

by Bob Carter on 6 May 2009 Never one to rest on its laurels, Yamaha has raised the bar with the release of two new 25hp four stroke models, the F25D and the FT25F. Both engines are sleek and stylish, being easily distinguished by the new graphics and the Yamaha tuning fork emblem mounted on the sleek cowling.

The two models are both four stroke engines and both designated as 25hp output at the propeller. The F25D is the standard model, while the FT25F is the high thrust version, best suited to operate on heavier boats.

While both engines share a common powerhead, the structural difference between the two lies in their drive train. The FT25F utilises the lower unit, bracket and gear box housing that is used on Yamaha’s F40 model with higher ratio gears. This gives the FT25F the gear ratio for turning a low pitch dual thrust propeller providing ample forward and reverse thrust for heavy boat applications such as barges or house boats.

Due to the varied applications of this four stroke outboard, the F25D is available in a multitude of different configurations. It is available as a tiller steer or remote control engine, with manual or electric starting, manual or power trim and tilt, and finally in a transom height of 20' for the standard lower unit or 25' for the high thrust model.

For the technically minded, both models have a twin cylinder four stroke powerhead that displaces 498 cm³. Weighing in at 78kgs, the standard F25D is in the lightweight category making it appealing for owners of inflatables, RIB’s, dinghies, and barra style boats. It is also an ideal kicker for trailerable yachts.

While EFI systems are common on Yamaha four stroke outboards from 30hp and above, Yamaha engineers have embraced the tried and tested single carburettor induction system on the new F25 models. The starting system includes a prime start system and decompression device. The prime start consists of a microcomputer that controls ignition timing and a carburettor to deliver precisely the right amount of fuel on start up. The decompression device ensures that manual or recoil starts are light and easy.

Combustion efficiency and therefore fuel efficiency when under way is achieved through the microcomputer controlling the ignition timing according to engine revs.

With the engine securely clamped to the transom of the boat, operators will find the F25 models easy to control and handle. All the essential engine controls are conveniently grouped on the front of the engine and within easy reach.

While some twin cylinder engines can be rough working through the powerband, Yamaha engineers have beaten the vibration problem with a counter balancer in the engine. The low vibration and low noise is top rate amongst outboards in its class.

Low exhaust emissions have for many years been a benchmark of Yamaha four stroke outboards. The Yamaha F25 is no exception. This engine exceeds the 2006 USA EPA emission standards and meets the US CARB emission standards and EU marine exhaust emission regulations.

Like all Yamaha outboards, the new Yamaha F25 incorporates a leading edge anti-corrosion system which provides exceptional protection of cooling passages and external components against saltwater and harsh UV rays.

There are five model variants, three in the regular F25D and two high thrust FT25D models

F25D:
F25DMHL (manual start, tiller handle, long shaft)
F25DEHTL (electric start, tiller handle, power trim & tilt, long shaft)
F25DETL (electric start, power trim & tilt, long shaft)

F25F:
FT25FETL (electric start, power trim & tilt, long shaft)
FT25FETX (electric start, power trim & tilt, extra long shaft)

Yamaha outboards are available through an Australia-wide network of authorised Yamaha outboard dealers. All Yamaha 4-stroke outboards are supported with a full four-year manufacturer’s warranty and all 2-stroke outboards are backed by a three year warranty – standard conditions apply.

Specifications

• Engine type: 4-Stroke / 2 Cylinders in-line
• Bore and stroke: 65mm x 75mm
• Displacement: 498cm³
• Performance: 18.5kW / 5500 rpm
• Full throttle operating range: 5000~6000rpm
• Weight (standard model): 78.0kg F25DMHL
• Compression 9.4
• Carburetion: Single with acceleration pump
• Oil capacity: 1.7 litres
• Lubrication system: Wet-sump
• Ignition System: CDI Micro-Computer
• Lighting Coil / Alternator: 12V – 13A
• Gear ratio: F25D 2.08 FT25F 2.42
• Starter system: Manual or Electric
• Starting system: Prime Start
• Steering: Tiller Handle or Remote control
• Trim: Manual or PTT