Yamaha F40B

A logical progression from the four-cylinder F40A (which was a de-rated version of the F50A), Yamaha's F40B is the closest, in features, of all four-stroke 40s to the EFI Evinrude 40 without incurring this engine's weight penalty. In electric-start power trim and tilt form the F40B is almost 16% lighter and 3% cheaper than its Evinrude competition, but still has some features lacking in Honda's BF40 (which is 5% heavier but 13% cheaper).

For example, the CD ignition has microcomputer control of timing advance and there's a cold-start fuel primer with air preheat, which acts like an automatic choke to warm the engine quickly from cold. And in electric-start versions, the 15-amp alternator still pumps out seven amps at a low 1000rpm.

The F40B is a three-cylinder, three-carbie version of the F25A and available in five different models, all of which come in long or extralong versions. The latter are useful for anglers who may have an older 4.3m Webster Twinfisher and want to switch from two-stroke to four.

In manual-start form the F40B weighs a reasonable 84kg. It comes standard with Hydro-tilt, a manual-hydraulic system that makes setting of shallow-water drive or full tilt remarkably easy, and has the advantage of allowing for trim changes underway.

The manual-start F40B also has a decompression device which opens the exhaust valves slightly while the engine is being cranked, reducing the starting effort required to about the same as the three-cylinder, two-stroke Yamaha 40. On the test day, I found that using two hands quickly overcame the initial compression and the engine fired up in a couple of seconds.

Mounted on a Quintrex Hornet 435 Trophy and pushing a three-adult load (total displacement 650kg), the demo F40B idled quietly, had plenty of power astern, and with its 80° steering angle, was easy to manoeuvre. It planed us on half-throttle and reached 50-51kmh over a 15cm chop.

Electric-start versions are available in four models, with a choice of Hydro-tilt or power trim/tilt in both tiller steer and remote control form. The one we tested was the remote control power trim model mounted on a Quintrex 455 Escape Runabout with Maxi Transom.

Spinning a 12-inch pitch alloy prop and pushing a three-adult load (total 750kg), the demo engine trolled at 750rpm and averaged 4.8kmh with significantly lower vibration levels than the F25A.

Although there was insufficient time to conduct fuel consumption trials, I estimate the engine was using 0.6-0.7lt/hr.

A clean plane was achieved at 29.8kmh on 4000rpm, and a fast cruise of 39.7kmh maintained on 5000rpm with pleasantly low noise levels at the helm. Over a 15cm chop the Wide Open Throttle (WOT) average was 46.1kmh on 5800rpm, where I estimate the fuel consumption to have been 13-14lt/hr.

However, there was excessive prop ventilation in tight figures-of-eight and perhaps a stainless steel prop with greater blade cupping would have helped here.

Although the F40B has a belt-driven camshaft, fortunately the engine is a non-interference type where pistons won't contact the valves should the belt break. Undercowl access is good, and the spin-on oil filter is easy to reach.

Recommended servicing intervals are every 50 operating hours or six months for the first two years after the 10-hour service, when the cylinder-head bolts must be tightened and valve clearances checked. After the first two years servicing is required every 100 hours or once a year, but I'd still change the oil and filter every six months regardless of how few hours were clocked up and use a heavy-duty diesel truck oil, if not Yamaha's own. The waterpump impeller should be replaced every 100 hours or once a year.

Well designed and engineered, the F40B provides a good blend of performance and fuel efficiency in a lighter package than all of its direct competition. And with regular maintenance, it should provide several years of low-pollution boating fun.