Yamaha Z200N

Though a long time coming, Yamaha's Z200N has been worth the wait. Its hydrocarbon and nitrides of oxygen levels are 30% below that required to comply with the US EPA 2006 legislation, yet it's lighter than its direct two-stroke competition.

In creating the Z200N Yamaha has taken its carbie 200 and narrowed the powerhead vee-angle from 90° to 76° and replaced the three dual-throat carbies with a high-pressure direct-injection (HPDI) system.

The HPDI injects fuel at three times the pressure, (50kg/cm2 or 750psi), of OMC FICHT engines using three separate fuel pumps. One is driven by alternating crankcase pressure, while the second is electric (3kg/cm2) and has a vapour separator. The third and high-pressure pump is operated by a toothed belt drive from the crankshaft and injects fuel particles at 20-30 microns, much finer than either the FICHT or Optimax spray pattern.

Instead of the FICHT Fuel Injection system, where below about 2500 revs the air/fuel ratio is 'stratified' in layers away from the spark plugs down to around 40:1, HPDI works on 'homogenous' combustion with an air/fuel ratio of 20-25:1 at all revs. At 2500 revs the FFI switches to homogenous combustion with about the same air/fuel ratios as the Z200N.

According to Yamaha, combined with the finer fuel particles this improves fuel economy by 20% over the direct competition and eliminates the 'flat' spots that occurred with earlier FICHTs at the changeover point. It should also eliminate the combustion chamber carbon build-up at low speeds. Of course, the Z200N would probably use more fuel at low speeds than the FICHT200 due to the richer air/fuel ratios.

And with their leaner fuel/oil ratios, designed to vary from 60:1 at Wide Open Throttle (WOT) to 300:1 at trolling speeds (though currently these ratios are slightly richer), the FICHTs should create less emissions at low speeds. In comparison Z200N ratios are 50-200:1 and oil is injected directly into the crankcase via the oil pump and six separate feed lines from an undercowl sub tank topped up from the main in-boat tank.

The six cylinders each have an independent throttle body air intake with butterfly valve connected to an oxygen sensor in the exhaust system and the Electronic Control Module This senses air temperature, barometric pressure, throttle and crankshaft position, fuel pressure, engine temperature and, of course, oxygen levels to maintain the correct air/fuel ratio regardless of load and barometric pressure. The ECM also advances the ignition timing for cold starts and reduces revs should the engine overheat or oil pressure drop off.

If the sensors, high-pressure fuel pump or ECM fail the engine can still function on the electric fuel pump. A laptop computer is plugged in to diagnose any faults.

Mounted on a Southwind SF655 and spinning a 17-inch pitch stainless steel prop, the demo Z200N provided much better acceleration in the 4000-5000 range than the same-propped carbie Yamaha 175 tested a few years ago on this hull. It started instantly hot and cold with no oil smoke apparent at any time and at low speeds (under 2000 revs) had none of the air compressor noise of its Optimax competition, although there was a slight whine from the high-pressure fuel pump.

Pushing a total of 1650kg (including four adults), it planed us at 3000 revs and 31.9kmh and cruised at 4000 and 55.0. At WOT it reached 5800 revs and 80.9kmh (6% faster than the 175) and used 68lt/hr (16% less than the carbie Yamaha 200). Vibration levels were comparable to the direct competition, but noise levels were lower and there was no prop ventilation at any time.

Servicing the Z200N appears straightforward with intervals recommended every 50 operating hours or six months for the first two years after the initial 10-hour service, then once a year thereafter.

Like its direct FICHT competition, the Z200N seems perfectly suited to the needs of owners having trailerable canyon-runners. All Yamaha has to do is reduce the recommended retail price in line with FICHT models and OMC will have a real adversary on its hands!