Hi guys. I've read all of this thread and would like to thank everyone for all the information I've gleaned from it. Right now I'm in the process of converting a Laser 240V to gas from glow ignition. As the photos show, the engine is a four-stroke 90 degree vee twin with one carb per 20cc cylinder. The beauty of this powerful engine is that it has a very low level of vibration, making it ideal for use in a wire-braced biplane. With glow ignition it's pretty thirsty and dispenses the usual large quantity of oil, which is why I want to convert it to gas, and I have a couple of questions about that.

Whilst a flat twin can use one dual-output ignition unit, this conversion needs two single ignition units each with its own sensor. The sensors are mounted on the crankshaft housing spaced at 90deg round the shaft, and a single magnet is mounted on the prop driver. I'm using two Rcexl ignitions, with the sensors mounted on a split ring clamp on the tapered and ribbed crankshaft housing.

For mounting the sensors and magnet I turned up a couple of aluminium ring clamps on my old Unimat 3 lathe. The rings are split and are secured by pinch-bolts. Photo 1 shows these rings. The left-hand ring fits the prop-driver and carries the magnet. The right-hand one has internal steps, which clamp on successive ribs on the crank housing. Also visible are the slits in the rings, the pinch bolt positions, and the sensor mounts screwed in place.

Photo 2 illustrates the ribbed crankshaft housing, and the prop driver in which the groove makes securing a magnet difficult.

Photo 3 has the rings and sensors in place. The magnet is a force-fit in its ring. The two grooves on the magnet ring are at 28 degrees spacing, which is the spark advance figure specified in the Rcexl instructions. When the groove at the rear of the magnet just exits from beneath a sensor, the attached ignition unit then activates to produce a spark at the appropriate time for the plug it's controlling. The second groove, which follows 28 degrees later, is set to TDC on No 1 cylinder when it is just exiting the sensor for No1 cylinder.

Photo 4 shows that the sensor installation is quite neat.

Initially I bench ran the engine to get used to adjusting two carbs, first on spark ignition and Laser mix glow fuel, and after half a gallon had gone through the engine I changed to 20:1 petrol:Evolution oil. At present the engine has the original Laser carbs. These were reasonably easy to set up on petrol for reliable running from idle to max revs with smooth transition through the range, though the main needles are very sensitive with only 1/4 turn between rich and lean, as is normal with glow carbs on petrol. Photos 5 and 6 show the test bench, and you can see that unlike the Japanese 4-strokes, the Laser carbs are mounted on the cylinder heads.

Photo 7 is the Laser 240V installed in my 27.5% scratch-built Jungmeister, along with its ignition system The two Rcxel units are secured with Velcro and a tie-wrap onto a liteply shelf, and an 8A Ubec atop that provides the 5V supply. The tortuous route of the plug leads keeps them well away from the hot silencers.

The underside view in the Photo 8 shows the fuel lines and the crankcase breather outlet, with its yellow/green flagged stopper to prevent drips on the hangar floor. The yellow Tygon tube pointing towards the prop-driver is the fuel tank vent, oriented forward as per the Laser instructions.

Photo 9 shows the engine fitting easily insie the cowl without having to cut holes for the plug caps.

Now comes my request for advice. When I bench ran the engine on ignition and gas, it handled really nicely. When mounted in the Jungmeister, it was again very tractable ….. until I pointed the fuselage nose-up, when the engine stopped every time. No matter how I adjusted the carbs, it always stopped. So clearly it needs a means of ensuring a constant head of fuel at the carb. Is it likely that simply pressurising the tank from one or both mufflers will suffice? Or should I fit a pair of proper gas pumper carbs?

As the engine is 20cc per cylinder, a carb sized for that capacity with induction pulse pump operation sounds as if it ought to do the job. However, I see that the Walbro WT-456-1 is now discontinued, but the Zama C1Q-P8-8YA has been identified as a viable substitute. Do you guys think that I ought to have a reasonable chance of success with a pair of Zamas?

Thanks

Gordon