Yamaha F9.9FS outboard engine review

There’s no getting around the fact that if you want low-emission power for a small tinnie you pay for it in weight. Four-stroke outboard motors under 10hp can weigh 50 per cent more than their two-stroke engine counterparts.

But does that weight penalty affect planing performance? Well no, because the twin-cylinder outboards between 8 and 10hp develop way more torque than comparable output two-strokes, so even though your tinnie’s transom is groaning under the weight the additional torque overcomes the greater bulk.

YAMAHA F9.9FS

Whereas the direct four-stroke competition are up-rated versions of their 8hp counterparts, the F9.9FS has a significantly bigger piston displacement by increasing the piston stroke from 40 to 43mm while retaining the same 56mm cylinder bore from the F8C. The powerhead still fits in the pan and under the upper cowl as the F8C but the dry weight is 39.9kg instead of 38, even though the F9.9FS is identical in every other design aspect.

The Yamaha F9.9FS outboard motor  develops 9.8hp at 5500rpm from its 212cc counterflow (non-crossflow) SOHC powerhead and has a Wide Open Throttle range of 5000 to 6000rpm.

Powerhead access is still good, with the sump oil dipstick easily reached, but as the sump holds only 0.8lt and there’s no external canister oil filter, oil changes should not be extended past 100 hours. If you do a lot of trolling, then I recommend every 50 hours or six months. The camshaft drive belt should also be checked every year for fraying.

As the Yamaha F9.9FS outboard motor is a carbie engine, there’s no performance advantage in using premium (95) unleaded. However, I would anyway, as it’s a way better quality fuel than standard (91), and don’t ever be tempted to use that garden weed killer known as E10. Yamaha SAE 10W30 4M oil is the way to go for ambient temperatures to 35°C but in the tropics use a 10W40 oil. Yamaha is a bit stingy with tools and a 12mm socket wrench is needed for the sump drain plug and a 17mm socket for the prop nut.

The recreational usage warranty is three years but with a little TLC this Yamaha should give at least a decade of reliable power.

ON THE WATER

Here’s the tricky bit. Every time I wanted to review the loan engine I had to psych myself into lifting it from a storage trolley onto the transom of my 3.6m Sea Al Super Skua tinnie. After six separate reviews afloat I decided I knew enough to be impressed, and with slightly larger biceps.

That said, all was forgiven once afloat and like its counterpart, the Yamaha F9.9FS outboard motor started easily hot or cold and didn’t blow any oil smoke. When trolling it ticked over quietly and smoothly, so no flab reduction there, or at any other time across the rpm range. Holeshot wasn’t as quick as a Tohatsu M9.8B outboard but then the Yamaha engine was pushing a total of 300kg compared to 285. As with the review Yamaha F8C, the standard 8.5in pitch alloy prop was used, compared to a 9.5 incher for the Tohatsu.

Because the Yamaha was so quiet and responsive in its upper rpm range I just wanted to drive it hard, whereas the Tohatsu really let me know it was being worked. For longer runs there’s just no getting away from these small twin-cylinder four-strokes.

THE TRADE-A-BOAT VERDICT

Yamaha has done a brilliant job of squeezing more torque and power from the long-running F8C. Left permanently bolted on a transom the OEDA 3-star F9.9FS is a logical low-emission choice for tinnies to 3.7m and being a Yamaha will return a good resale price.

As of December 2013 the Yamaha F9.9FS shortshaft version has a price of around $3600 and a spare prop costing $150. Thanks to Yamaha Motor Australia, Murarrie, QLD, phone (07) 3906 7000, for yet another beautifully-made outboard motor.

YAMAHA F9.9 OUTBOARD SPECIFICATIONS

TYPE  Two-cylinder four-stroke petrol outboard motor

RATED HP 9.8

DISPLACEMENT 212cc

BORE x STROKE 56 x 43mm

WEIGHT 40kg (short shaft); 41kg (long shaft)

YAMAHA F9.9FS vs TOHATSU M9.8B

YAMAHA F9.9FS

TOHATSU MFS9.8

* Loop of cruising with 10 per cent WOT and 40 per cent trolling, averaging 8kts, saw an average fuel burn of 1.8lt/h and 6.6 hours per 12lt tank for the Yamaha, and 2.5lt/h and 4.8lt respectively for the Tohatsu. Sea-trial data supplied by the author.

THE COMPETITION