Flamethrower attempt

Cole Emslie

New Member
Joined
Jun 6, 2018
Messages
11
I have 2 bikes and on of them will pop after being run hard. The other one has only popped once, but on a top speed run you can see occasional flames. Currently, I have to run the bike really hard, usually up a long hill, and hold in the kill switch while WOT and it will pop a few times. However, I have a new idea. I want to mount a spark plug in the exhaust. I will place this about 2/3-3/4 down the muffler. The muffler is gutted to about halfway (My "quiet" bike). I have a coil like unit that can run off of a 9 volt battery that indeed fires a plug. I will open the spark gap substantially. The goal is to be able to hold the kill switch and a small momentary switch, or tie the 2 together, causing raw fuel to be pushed into the exhaust and ignited. Don't tell me its a bad idea or could cause damage as it is my last summer before college and will be my last summer with the bikes. btw the coil thing I have is a cheap unit from ebay that claims to generate 80,000 volts and can throw HUGE sparks (over 2 inches). When i hooked it up to an old plug, it was an insanely bright spark even with the gap increased. Any input?
 


Cole Emslie

New Member
Joined
Jun 6, 2018
Messages
11
Well I didn't have much homework today so I built it. I will include pictures and maybe a video of it soon upon request. It doesn't look pretty, but the spark plug was the simplest option and its all I had on hand. I ran a 9v battery to the unit and drilled my handle bar so a push switch is on the left side. I didn't get to test any real speed as it was dark and it was really cold and there is some black ice (Minnesota). However, it would ignite during idling (very rich due to a summer tuneup setting) and I did get it to pop by holding the killswitch while going ~15. Very nice blue flame and a good sound. It sounded better under speed of course, and can't wait to try it at near top speed. It did also pop sometimes while the engine was running (~10 MPH) and one of the pops made the engine sputter. I don't think the flame would have much force behind it as the muffler has a good amount of baffles remaining and a closed pipe inside with holes on the outside (It's a weird pipe design that I have never seen). I bet the sputter was due to excess back pressure. It is my spare beater bike with over 3000 miles so I don't care too much. This system would cost between $5-10 for anyone to build. The plug just threaded into the side of the pipe, but I may get a nut to secure it from the inside as well.
 

Cole Emslie

New Member
Joined
Jun 6, 2018
Messages
11
Lets see a video!
I just mounted a goPro and will get a video once it warms up. I did not feel like riding with a windchill of 4 degrees. Quick correction, the unit wants an input of 3-6 volts. I will replace the 9v with a 4 volt 18650. Still produces a great spark, but hopefully will prevent the unit from burning out. If the forecast is correct, I will ride Friday.
 
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