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An Interesting Gas Engine Ignition Problem

Learn how David Cave managed to resolve an ignition problem involving his 1910 4hp battery and coil powered Waterloo Boy engine.

| February/March 2020

waterloo-boy
Author David Cave's 1910 4hp Waterloo boy. Poor running got David looking closely at ignition dwell.

Some time back, I acquired a 1910 4hp battery and coil powered Waterloo Boy engine with an interesting problem. Today I say it had an interesting problem, at the time I used less complimentary terms.

It’s a big engine with good compression, difficult for a 70-plus-year-old man to start. I’d pull it up on compression slowly, then give it all I had to pull it over before it kicked back. It seemed to have no retard mechanism. Most often it would get off a weak hit and then come around and get off a good hit. The engine speed would then be in the neighborhood of 200rpm-300rpm. At that point the engine would quit firing, even though the igniter was tripping, and the RPMs would rapidly start dropping towards zero. At about one revolution per second, just as I thought it was dead, it would have another good hit. With that hit the RPMs went back up again — and we’d start the process all over again: a hit to gain RPM, then die till the RPMs were low. This would go on about as long as I’d let it.

Looking for a Solution

I spent the better part of a day playing with the mixer, choke, cam timing, valve timing, igniter timing and about anything else I could think off. Finally, in desperation, I got my ohmmeter out and checked the dwell angle. The igniter points closed at 35 degrees BTDC and the igniter tripped at 20 degrees BTDC. I had only 15 degrees of dwell.



In the early 1900s, battery- and coil-powered engines kept igniter points open as long as possible in order to conserve battery power. With my points being closed only 15 degrees of crank shaft rotation, the actual clock time the points were closed was very short. At 300rpm the igniter points were closed only 8ms (0.008 second) before the igniter trips, but at the much lower speed of say 60rpm, the points were closed for 42ms (0.042 second) before the igniter trips.

oscilloscope-screenshot
A screenshot from David's Oscilloscope showing the rise of coil current across time in the coil used on the Waterloo Boy engine.



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