The diminutive yet indomitable Honda EX350 portable generator was introduced in 1987 and was the second-generation domestic generator from Honda. Notably it was the world’s first to introduce an inverter circuit. This was achieved though some wonderful engine miniaturisation to turn a three-phase multi-pole (15 poles AC and 6 poles DC) high-speed stator which, via an intermediate DC regulator/rectifier was then reconverted back to mains voltage AC current through a simple invertor. All standard stuff these days but novel at the time. The sine wave was a simple 50 Hz modified-square, but the important point was that it was stable.
The domestic generator market was aimed at those who wanted to power ‘in the field’ the likes of small radios, stoves and lighting at campsites, festivals etc. Nearly all electrical devices are designed to run on a stable pure-sine wave (mains) AC current and do not work well if the waveform is fluctuating. Previous generators had a messy, fluxating waveform that led to erratic operation from plugged in electrical devices. A simple, but stable modified-square wave was a big improvement and, at only 8.5 kg, the Honda EX350 was a hit with consumers and produced in considerable numbers. In 1996 Honda introduced the EX500 which packed a little more punch and had a true sine waveform. The EX500 wasn’t produced for long before Honda released their (world first) microprocessor-controlled sine-wave inverter 4-stroke generators.
To keep the EX350 light, Honda used a 35 cc 2-stroke with everything running through a unique crankshaft design on a single axis. The pull starter mechanism was integral to the top crankcase and the stator doubled up as the flywheel. The little EX series were the only 2-stroke generators Honda ever produced and, as this type of engine just cannot meet modern emission laws, are likely to remain as unique examples. While most mains devices and power tools from several decades ago were rated at less than 300 Watts, they are considerably higher now and beyond the ability of the EX350. Even if the rated wattage is low enough, they likely require the high energy peak of the sine wave which is absent on a modified-square wave. Finally, for short length excursions, lithium power packs have made the need to run portable devices from an internal combustion generator a thing of the past. Still, the high level of engineering inside is fascinating and for that reason alone I have one myself (oh and it’s red; my favourite colour!).
Like most things Honda, the EX350 is pretty bullet proof and will keep going for years with minimal issues. Indeed, I would hazard a guess that most chug away with the bare minimum, if any maintenance. That said, the 2 stroke engines in the EX350 were initially marketed as requiring a 50:1 oil mix; likely to guarantee sufficient lubrication in cases of slap-dash oil mixing and reduce returned units. This really was too much oil and caused a build-up of carbon within the exhaust manifold and silencer. If left unchecked this would begin to restrict exhaust flow and at worst, carbon granules could detach and be drawn back into the engine to score the piston/liner. Scoring wouldn’t kill the engine but would slowly chip away at engine efficiency and peak power output. Repair at this point would be uneconomical. Honda later amended the ratio to 100:1 (1% oil) which made things much cleaner all round but many are still likely run on 50:1. Either way the fix was simple; remove only a few bolts to periodically remove and clean the manifold of carbon build-up. My own EX350 has also been treated to a carburettor strip down, new air filter, spark plug, fuel lines and a good clean inside and out.