Magneto information.

fdnjj6

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Aug 17, 2019
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Hello everyone. I have come up with a plan to make a rev limiter (possibly 2 step) for my motorized bicycle. There are 3 wires coming from the magneto and I have found out that according to some people, the white wire produces 6-9volts AC. I am wanting to figure out how much voltage and current is typically pushed out of the blue and black wire on a stock magneto with a stock magnet. Also, is the voltage DC or AC? The plan is to have a mosfet or transistor controlled by an arduino cut power to the cdi when the arduino reads the rpm where the rev limit should engage. I have built a system to ignite the fuel and air mixture is in the exhaust when the kill switch is being pushed causing flames to shoot out the exhaust pipe. The idea is to have the arduino control the kill switch action for me so it keeps the engine under a steady rpm and reliably shoot flames. Any help and information is greatly appreciated. Thanks!
 

fdnjj6

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Also, if anyone has any specific transistors/mosfets that would suite this project well that'd also be very appreciated. Since I am relatively new to mosfets any info would be great to hear. I am comfortable with NPN transistors but I'm afraid those will waste too much power. I am still learning PNP. My understanding of mosfets is that they exist in P channel and N channel and that there are enhancement and depletion types. Since I want to use an arduino I would want an enhancement N channel type correct? And if I'm not mistaken, transistors turn on and off based on current at the base and mosfets turn on and off based off of voltage at the gate. Correct me if I'm wrong and once again any further help of info is greatly appreciated.
 

Jimmy Bloodmaker

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Nov 24, 2018
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Also, if anyone has any specific transistors/mosfets that would suite this project well that'd also be very appreciated. Since I am relatively new to mosfets any info would be great to hear. I am comfortable with NPN transistors but I'm afraid those will waste too much power. I am still learning PNP. My understanding of mosfets is that they exist in P channel and N channel and that there are enhancement and depletion types. Since I want to use an arduino I would want an enhancement N channel type correct? And if I'm not mistaken, transistors turn on and off based on current at the base and mosfets turn on and off based off of voltage at the gate. Correct me if I'm wrong and once again any further help of info is greatly appreciated.

to rev limit a 2 stroke, it's all in the ports and pipe. no need for extra fancy stuff. i port mine for about 8000 rpms, or less. all depends on what i wanna use the engine for. to hit 8000, i take about a 1mm off the roof of the exauhst and widen by .5 mm-1mm each side, widen my tranfesr ports by .5 mm-1mm ( each one of them) and widen my intake by .5-1mm of the jugs from the supplier i get. i also trim the piston skirt to match the intake and gasket match. i usually rev out at about 7800-8000 rpms. my supplier is pretty consistent with their jugs. it's why i keep buying them from them though. i know what i am getting every time and it makes it easier for me to build my engines. usually a stock motor will only rev to around 6000-6500 rpms. not including the special kits like zeda, bbr, gasbike etc release. you can also rev limit by merely putting a washer or two inside the top of the slide to prevent it from opening the carb throat all the way. a lot cheaper and more cost effective then using an adrino.
 

Jimmy Bloodmaker

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Nov 24, 2018
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oh and the output is always ac when dealing with a magneto on these bikes, unless you toss in a diode, but tht will mess up your cdi and possible prevent it from firing at all. the cdi uses both sides of the wave. an the white wire can be 12v. really it depends on the maker and how they wound it. the output on these is usually maxed out at around 1.5 amps, if even tht. i believe the input from the cdi side of the coil is 250v, more if you use a super magneto, has more winding's. i believe those output at around 350v. any higher and it will cause the cdi to fire to soon.
 

fdnjj6

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Aug 17, 2019
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to rev limit a 2 stroke, it's all in the ports and pipe. no need for extra fancy stuff. i port mine for about 8000 rpms, or less. all depends on what i wanna use the engine for. to hit 8000, i take about a 1mm off the roof of the exauhst and widen by .5 mm-1mm each side, widen my tranfesr ports by .5 mm-1mm ( each one of them) and widen my intake by .5-1mm of the jugs from the supplier i get. i also trim the piston skirt to match the intake and gasket match. i usually rev out at about 7800-8000 rpms. my supplier is pretty consistent with their jugs. it's why i keep buying them from them though. i know what i am getting every time and it makes it easier for me to build my engines. usually a stock motor will only rev to around 6000-6500 rpms. not including the special kits like zeda, bbr, gasbike etc release. you can also rev limit by merely putting a washer or two inside the top of the slide to prevent it from opening the carb throat all the way. a lot cheaper and more cost effective then using an adrino.
Thank you for the information. I'll probably use that to port my cylinder since that was a plan for the future. My plan is to rev limit up to about 3000-4000 rpm to shoot flames and have my port timing/tune to basically rev limit for full throttle high speed pulls. I specifcally need the spark to be cut so that the engine keeps pushing unburned air fuel mixture into the exhaust to keep the flames going.
 

Jimmy Bloodmaker

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Nov 24, 2018
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naw, you should just use an injector and a lead to a amplifier to a plug in the tail pipe. this way you can control the flame size without adversely effecting your engines operations. you risk fouling up the plug attempting to run a two stroke with a spark cut. besides, a small fuel pump, run from a batt charged by the white wire connected a rectifier. you could then use your adrino, powered by the bike mind you, to send signals to the pump and plug to flame out like you want. big flames, little flames, roaring **** fire!! if it was me, i would cut out the white wire and use just a plain old batt i charged when i got home. robs less power from the engine and wont freak out and cause some feedback loop or resonances tht blows the tiny wires inside it.
 

Jimmy Bloodmaker

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Nov 24, 2018
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you could even tie in a small signal lead to the adrino to fire the tail plug only when the main plug fires. then use the adrino to set the dwell time for the coil to the tail plug so you get a huge spark and make sure all the fuel lights up.
 

fdnjj6

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Aug 17, 2019
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Thanks for the suggestion but I already have the flames working. I have about 4 spark plugs that I can use and they're cheap so I'm not worried about them fouling on me. Last time I had the head open there was very little carbon build up ever since I rejetted and ran a better oil. The only downside is that the bike will occasionally backfire though the carburetor due to my inconsistencies with the kill switch. The revs drop too low and that gives more time for the flame to travel through the whole intake when spark is re introduced. Sometimes I will take a second too long to push the switch and it'll rev really high so I'm really wanting it to be elctronically controlled. I'll try to post a video of it shooting the flames so you can see what I mean.
 
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Jimmy Bloodmaker

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or an even more simple way, a small hole screen on the inside of the intake. just make sure the motor dont suck it in and tht it stays free from clogging. will hurt performance, the other two will not, but will work on the cheap. think spark arrest screen on an exhaust.
 

Jimmy Bloodmaker

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Nov 24, 2018
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Thanks for the suggestion but I already have the flames working. I have about 4 spark plugs that I can use and they're cheap so I'm not worried about them fouling on me. Last time I had the head open there was very little carbon build up ever since I rejetted and ran a better oil. The only downside is that the bike will occasionally backfire though the carburetor due to my inconsistencies with the kill switch. The revs drop too low and that gives more time for the flame to travel through the whole intake when spark is re introduced. Sometimes I will take a second too long to push the switch and it'll rev really high so I'm really wanting it to be elctronically controlled. I'll try to post a video of it shooting the flames so you can see what I mean.
to get it to rev high, you are gonna need to port it. doesn't matter where the spark is, if there just aint enough flow it wont go there.
 

fdnjj6

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Ooh I like that idea. That should help and I could window my piston to gain power with the reed valves.
to get it to rev high, you are gonna need to port it. doesn't matter where the spark is, if there just aint enough flow it wont go there.
Yea that's what I figured. Top speed is 37 mph right now. Still have a little bit of tine tuning to do. My main concern is just getting a rev limiter setup for low revs. Like 3-4 maybe 4-5 thousand rpm. Would you happen to know whether the blue and black wires output ac voltage? If they do, then that would probably either fry or not with with my transistors or mosfets right?
 

Jimmy Bloodmaker

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Nov 24, 2018
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Yea that's what I figured. Top speed is 37 mph right now. Still have a little bit of tine tuning to do. My main concern is just getting a rev limiter setup for low revs. Like 3-4 maybe 4-5 thousand rpm. Would you happen to know whether the blue and black wires output ac voltage? If they do, then that would probably either fry or not with with my transistors or mosfets right?
yeah, all the voltage from any coil, even the white, is going to be ac on these stator coils. if you try to rectify it before the cdi, the cdi most likely wont fire. i believe the stock voltage is around 250v ac at 3k rpm, don't quote me though. i think the stock cdi takes tht 250 and smacks it up to 25k for the plug.
 

Jimmy Bloodmaker

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37mph aint bad. my fastest bike is 46 mph currently. i'm working on joining the 50mph club. th 40mph club almost got me killed when i blew a motor and locked it up trying to get the last tenth of a mile to hit 43. tht was one jeba of a ride. lol. when i first hit 46mph on a different bike, i was like hall yeah!! then i blew the chain and luckily it didn't hit me as it flew off in to the road.
 
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fdnjj6

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37mph aint bad. my fastest bike is 46 mph currently. i'm working on joining the 50mph club. th 40mph club almost got me killed when i blew a motor and locked it up trying to get the last tenth of a mile to hit 43. tht was one jeba of a ride. lol. when i first hit 46mph on a different bike, i was like hall yeah!! then i blew the chain and luckily it didn't hit me as it flew off in to the road.
Jeez yea that's what I'm hoping to avoid. If you can, you should hover your hand over the clutch so the instant something doesn't go right you can pull it in and as long the engine itself locked up you'll likely be fine. If it's the chain however, you'll just have to bank on luck with that one. lol What kinds of upgrades did you run to get 46 mph? I won't be upgrading mine to go that fast since I like the extra torque I get from running a bigger sprocket since I live near a few big hills. However, I think the upgrades I'd have to do is a bigger sprocket, porting for higher revs, and maybe up the compression a bit.
 

fdnjj6

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Aug 17, 2019
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37mph aint bad. my fastest bike is 46 mph currently. i'm working on joining the 50mph club. th 40mph club almost got me killed when i blew a motor and locked it up trying to get the last tenth of a mile to hit 43. tht was one jeba of a ride. lol. when i first hit 46mph on a different bike, i was like hall yeah!! then i blew the chain and luckily it didn't hit me as it flew off in to the road.
Are there actual clubs for breaking certain speeds? Are there any other rules to the 40 mph club besides being able to hit 40 mph? Or do you have to hit 40 mph within a certain time limit? Since mine is hitting 37, I might shoot for the 40 mph. I still have some jet fine tuning to do so that might bump me up another 1-2 mph.
 

FOG

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The Southern California Timing Assoc. aka SCTA has a really cool licensing system for land speed racing at the local dry lakebed. Kind of like a minor league for Bonneville.

I personally have an "E" license that's good to 124mph.

A "D" license gets you to 149mph.

"C" is up to 174mph.

"B"'s can go 199.

And now you know what it takes to get an A in this class.
 

FOG

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Got nuthin' to do with the original post but you guys might get a kick outa this video. I was there that day but as usual was looking the wrong way. All I saw was a cloud of dust.

The pilot did survive. Had a lacerated leg, one collapsed lung, and his bell rung but good! Lived to tell the tale tho.

 

fdnjj6

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Aug 17, 2019
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Got nuthin' to do with the original post but you guys might get a kick outa this video. I was there that day but as usual was looking the wrong way. All I saw was a cloud of dust.

The pilot did survive. Had a lacerated leg, one collapsed lung, and his bell rung but good! Lived to tell the tale tho.

Sheesh that's gotta hurt. How fast was he going when he flipped?