Yamaha CV85

Introduced locally in 1992 as a cheaper alternative to the oil injected 90A, the 50:1 pre-mix CV85 is actually based on the 75A released here in 1982.

The CV85 could be regarded as a 'first generation' two-stroke and has mechanical ignition timing advance, electrically-operated manual choke and no lower cowl-mounted trim/tilt switch.

But it does have some advantages over the 90A, which has electronic timing advance for both normal operation and cold starts.

One advantage is that the mechanical advance gives more instantaneous throttle response than the 90A's microprocessor system. Another is that, because the petrol/oil mix runs through the three carbies, the residual oil protects the throttle butterfly valve shafts against verdigris buildup. And because the motor operates on 50:1 at all times, much more residual oil is left on the bearings and cylinder bores during periods of disuse, protecting the powerhead far better than the 90A, which idles at 200:1.

As many older boaters know, running a premix outboard from an underfloor fuel tank can create problems such as not knowing how much oil to add when topping up the tank and the fuel 'going off' after a couple of months of disuse.

Unfortunately there's still the first problem, which can be solved by adding the fuel/oil mix in batches of a couple of litres until the tank is full.

But with the advent of Isopropyl Alcohol in the past decade the stale fuel problem is a thing of the past. Just add Yamaha's 'Fuel Conditioner and Stabiliser' to the fuel as you top up the tank and the fuel will remain 'potent' for up to one year.

For storage use, mix the fuel and additive at 125:1. For normal usage, use a 250:1 mix to reduce moisture buildup and combustion chamber deposits. The spark plug electrodes will always have a slightly wet appearance due to water absorbed by the additive, but this won't affect normal operation.

Because of its understressed powerhead, with only a 5.1:1 compression ratio, the CV85 suits commercial applications as well as recreational. The demo motor easily handled two or four adults aboard the Southwind UB520 Classic test hull.

Despite the absence of a cold-start fuel primer, the demo motor fired-up within 20 seconds of turning the ignition key and warmed quickly from cold.

As it was still running on the 25:1 break-in mix (first ten hours), it was fairly smoky below 2000rpm, but above these revs no smoke was apparent.

Provided the anti-ventilation plate was kept at least three-quarters immersed, power astern was good and no cooling water starvation occurred. At all times the pilot water discharge was clearly visible.

Spinning a 17in pitch alloy prop and pushing a total of 800kg, including two adults, the demo motor trolled at 3.9kmh on 600rpm. Vibration levels were slightly higher than a 90A tested a while back. We achieved a clean plane at 27.5kmh on 3000rpm, and the motor cruised quietly and with comparable vibration levels to the 90A at 44.5kmh on 4000rpm consuming 11.7lt/hr. There was no prop ventilation through tight figures-of-eight.

We averaged 62.0kmh at Wide Open Throttle (WOT) on 5400rpm using 29lt/hr and could hold a normal conversation at the helm despite being only a couple of metres from the motor.

Pushing a four-adult load totalling 960kg, the CV85 planed us cleanly at the same speed as the lighter load but on 3400rpm. We cruised at 42.0kmh on 4000rpm, and the WOT average was 58.4kmh on 5300rpm.

As there's no undercowl oil tank, powerhead access is even better than the 90A. The three carbies, ignition timing advance linkages, spark plugs and water-separating bowl type fuel filter are all easily reached. Recommended servicing intervals are every 100 hours or once a year (also for waterpump impeller replacement) after the first ten hours, then every 50hrs for the first two years.

For recreational applications the warranty coverage is two years, and according to 90A owners interviewed, the CV85 should survive saltwater usage very well.