With its traditional four stroke engineering, such as a one-piece crankshaft and capped connecting rods, the F9.9 is almost a throwback to the old US cross flow two stroke outboards, nonconventional Japanese two stroke designs that have multi-piece crankshafts and solid con rods providing have nowhere near the longevity.
IN THE DETAILS
The F9.9 has a ‘counterflow’ power head, where the intake and exhaust manifolds are on the same side, making for a compact engine. The four valves are operated by a belt-driven camshaft that’s designed to last 800–1000 hours before needing replacement. But if it does break, the engine is a ‘non-interference’ design where the pistons won't contact the valves. Still, checking the timing belt annually for any fraying or damage is good precaution.
Unlike its two-stroke competition, the F9.9 has electronic ignition timing advance to improve running qualities and reduce servicing costs. A 6200rpm limiter protects the engine. The timing advance also allows the F9.9 to run on either 91 RON unleaded or 95 premium, not possible with four strokes that have fixed timing, such as Yamaha’s F2.5B. Using 95 means there’s less chance of buying fuel tainted with that weed killer AKA ethanol.
Originally, the F9.9 could only be transported on one side to prevent sump oil flooding the combustion chambers, but the current model can be laid or transported on its back, just like a two-stroke outboard. Early models had a cold-start choke, then a fuel primer. Now it’s back to a choke. Phew!
Available as an option is a DC rectifier for the 12V 6A alternator to charge batteries where electric starting is not fitted.
Checking oil level in the 0.8 litre sump is easy using the dipstick provided but having a relatively small capacity, I'd change the oil every 50 hours instead of the recommended 100 if doing a lot of trolling between oil changes. Under light loads at trolling rpm, where the engine temperature may drop to as low as 45 degrees, there’s a fair amount of condensation ‘blow by’ (a by-product of burning petrol) past the piston rings and this dilutes the oil, reducing its ability to lubricate the engine under higher loads, such as when planing. I suggest using Yamaha’s own SAE 10W30 for all but tropical climates. Yamaha’s recommended servicing intervals are every 100 hours or annually after the first 20 hours or three months. A 12mm socket box spanner (not supplied in the toolkit supplied with the loan engine) is needed to remove the sump drain plug.
Four trim and two shallow water drive positions are supplied, enabling the F9.9 to be used in skinny water, and the cooling water intakes located directly above the gear case torpedo enable the engine to be quickly fresh water flushed after salt water runs using small muffs. This ensures only clean water flushes out the cooling water passages and is way preferable to using a flushing drum. Alternatively, in later models, the F9.9 can be flushed without running the engine. Prop swapping is straightforward using a 1mm box spanner to remove the castellated prop nut.
BUYING A USED F9.9
As this engine has been around long enough for second-hand models to be available, what are the main issues to consider?
The main issues are power head overheating, leg and lower unit corrosion and sump oil colour.
Overheating is indicated by paint bubbling or discolouration around the cylinder head, while paint bubbling on the leg and lower unit indicates insufficient washing down with fresh water after each run. Paint abrasion on the prop blades indicates the engine has been run in very skinny water which of course accelerates water pump impeller wear.
The sump oil should be a pale honey colour. If dark brown or black, it indicates the oil has been changed infrequently. Whenever I acquire a second-hand four-stroke engine, I always change the engine oil (and filter where fitted) before using the engine under load. Oil is cheap compared to rebuilding a worn power head.
I recommend mounting the engine on a transom, checking the oil level while the engine is vertical, then connecting the flushing muffs and turning on the water. Attach the fuel line and squeeze the primer bulb until firm. Pull out the primer/choke knob, then slowly crank the engine to check for any piston ring binding. If the engine rotates freely (it should due to the decompression starting) then pull the starter cord until it engages with flywheel. Pull the cord rapidly and once the engine has started, check for water squirting out of the pilot water discharge or tell-tale. Run the engine for at least ten minutes. The power head should be warm by then but not too hot as it would be after a run at planing speeds.
While the engine is running, stand well clear of the prop and engage forward and reverse gear. The engine should clunk into gear, indicating the clutch dogs aren't worn.
USED PRICING
According to Ralph Merkel of Newcastle Yamaha Marine, up until the banning of carbie two stroke outboards in Oz in 2019, the F9.9 was overshadowed by the two stroke 15F. Sure, long shaft high thrust models were sold for house boats, with regular reports of at least 3000 running hours possible without major servicing, but it’s really only since 2018 that the short shaft F9.9 became popular.
Ralph told me that a four-year-old F9.9 in good condition is worth at least $1500.
ON THE WATER
The 2009 loan F9.9 performed brilliantly on the Super Skua, starting instantly hot or cold and with its effective thermostat warming quickly from cold. Vibration levels across the entire rev range were very low, giving me a chance to retain my arm flab and at or near Wide Open Throttle, the engine was much quieter than its two stroke competition. At all times, the strong-flow pilot water discharge was clearly visible and the upfront gear shift made operating the engine a delight.
Despite being a four stroke, the loan engine accelerated reasonably quickly out to WOT and through tight turns there was no prop ventilation.
Over a total of 13.2 hours of saltwater leg/lower no corrosion was apparent anywhere on the loan engine.
THE WRAP
Yamaha’s F9.9 has come a long way since the original model was released on the Aussie market back in 1985, though the one I tested back then was a damned good engine. It overcomes its hefty weight by simply developing so much midrange torque.
Yamaha knows how to make a great four stroke outboard and the F9.9 is no exception. And according to Ralph, Yamaha has over 50 per cent market share of all new outboards sold in Lake Macquarie and Newcastle. That’s some recommendation!
Google Yamaha Marine – Yamaha Motor Australia for your nearest dealer.
SEA TRIALS
Single F9.9 on 3.6m Sea Al Super Skua tinny, swinging the standard 8.5 inch pitch alloy prop and pushing a total of 300kg, including two adults and fishing tackle. Average of two way runs in calm water on Lake Macquarie NSW. Range is in nautical miles for the standard 12 litre plastic remote fuel tank with a 10 per cent reserve.
**Note cruise range better than just planing due to faster hull speed relative to fuel flow. Also, the WOT range is only marginally less than when cruising indicating engine efficiency across the planing range. I suggest not operating the engine continuously above 5000rpm.
“Loop” of cruising including 10 per cent WOT operation and averaging 8kt:
LT/H 1.8
NM PER TANK WITH 10 PER CENT RESERVE 48
QUICK SPECS
YAMAHA F9.9
ENGINE TYPE Counterflow twin cylinder four-stroke outboard
RATED BHP/MHP* 9.8/9.9 at 5500rpm
REC WOT RANGE 5000–6000rpm
DISPLACEMENT 212cc
BORE X STROKE 56 x 43 mm
GEAR RATIO 2.08:1
DRY WEIGHT 39kg short shaft
RRP JUNE 2017 $3199
RRP AUGUST 2021 $3420
OEDA STARS 3
*Brake horsepower/metric horsepower or PS