Splicing a circuit: custom project

[oldunion]

My intention is to have a spark jump across the exhaust hole of a small gas powered scooter i have. During tests with a tazer, this has the effect of creating a small blue flame that burned excess gas (exactly what i want).

This is a 62 cc 9hp aplication. I figure that if i run spliced off the wire from the magneto (this is a weedwacker engine we are dealing with) then i could then run this wire to the exhaust and have it jump across. However, i do not know what adverse effects this would have on the performance of the engine; i believe i once learned that dividing a voltage drops it in half, so...expert opinions?

 

[berkeman]

I would install a secondary ignition system, and just drill and tap the exhaust for a spark plug. Run the second ignition system straight from the battery, and make an adjustable trigger circuit so you can play with the timing and advance to try to catch the exhaust pulses as they leave the exhaust pipe.

 

[Danger]

My high-school buddy did the same thing with his LeSabre. It was a 340 Buick motor (that's not a typo) with major racing mods. He ran it a bit rich, and there was significant valve overlap. His mufflers were straight-through Baby Thrushes with the baffles removed.
So... he mounted a distributer/coil assembly in the trunk, turned by a 12V fan motor, and ran the wire to a spark-plug screwed into the H-pipe. If someone was tailgating him, or just for fun coming to a stop sign, he'd downshift and hit the switch. Nothing makes a guy back off faster than seeing two half-metre fireballs flying at his windshield.

 

[oldunion]

I already tried to mount a second ignition to be powered by the sparkplug. Its definitely possible, but at this time i lack the needed tools to make it good and not makeshift.

To alter the timing i would need to mess with the flywheel and i can't do that because i still need to run a high performance racing engine off of it. The thought of just screwing in a spark plug does sound attractive, however.

So for now, i am left exclusively with the option of just splicing the wire. Is such a thing conceivable?

 

[berkeman]

No, I would not try to split the ignition wire, if that's what you are saying.

 

[Danger]

i lack the needed tools to make it good and not makeshift.

All you really need to do is install an electric buzzer in series with a transformer and switch. Take the spark from the transformer output. If you want it to be synchronized with your engine spark, use an inductive pick-up on your primary plug wire as a trigger.

To alter the timing i would need to mess with the flywheel

Why would you want to alter it?

 

[oldunion]

All you really need to do is install an electric buzzer in series with a transformer and switch. Take the spark from the transformer output. If you want it to be synchronized with your engine spark, use an inductive pick-up on your primary plug wire as a trigger.


Why would you want to alter it?

i thought someone mentioned timing...

Im afraid i did not understand a thing you said. Could you dumb it down for an international studies major?

 

[Averagesupernova]

Someone DID mention it. But they weren't talking about the timing of the engine itself. Do like danger said.

 

[Danger]

Oldunion, an electric buzzer works by having the armature be the noisemaking part and also part of the circuit. When energized, the solenoid pulls the armature against the bell or whatever, but also pulls it away from the contact point with which it mates to complete the circuit. That, of course, shuts off the solenoid, and a spring snaps the armature back into contact. Then the cycle repeats. If you put the primary coil of the transformer in series with it, that gives you your collapsing magnetic field which is necessary to induce a current in the secondary coil of the transformer. Think of the buzzer as being the points in your magneto or a car distributer. A seat-belt warning buzzer and automotive coil should work fine. Make sure that the coil is well grounded, or the plug won't fire.
And you don't really need to tap the hole for the sparkplug if it's reasonably thin tubing in your exhaust. Just drill a hole slightly smaller than the outer thread diameter and screw the sucker in with a wrench. The threads on it should be sharp enough and strong enough to cut their own path. Elsewise, you can make a bigger hole and put a nut on the inside.
I wouldn't worry about timing the spark to match the pulses in this case. Buzzers are fast; it should fire several times per engine revolution no matter what your tach says, so all unburnt fuel will encounter a spark.
Good luck, and keep us posted on your results.

 

[Danger]

PS: If you want to have even more fun, put a small gasoline or acetylene injector just ahead of the sparkplug.

 

[berkeman]

PS: If you want to have even more fun, put a small gasoline or acetylene injector just ahead of the sparkplug.

...and you wonder where Danger got his PF handle...