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Discussion Starter · #1 · (Edited)
hey guys, I just recently purchased a 1974 yamaha dt250. when i bought the bike the wiring harness was in a spare parts tub the guy had, it was still intact but theyre torn up pretty bad, an ignition coil, the run/stop engine switches, along with the gauges and key, but a battery was no where to be found

I understand that this bike produces power with the magneto, and i know that its producing spark, sparked on top of motor when i kicked, I have tried and tried to get this thing to start with just the magneto, and it has sputtered a couple times, but never fired. I've tried spraying carb clean in the intake(i'm slightly inclined with automobiles, lol) I've tried a little premixed gas, and I've tried straight gas, I've rebuilt the carburetor and made sure the floats weren't stuck ... but she's still never FIRED

it has sputtered on all three ... but only a couple times, which brings me to my question
does the main harness have to be in the bike? would making a new harness and at least attaching a 12v battery(any idea on size because if i get it running im doing anyway) produce any more spark? does it have to have the key?

thanks in advance everyone
 

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sickboy
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First things first that bike has a 6v system and takes a 6v battery so DO NOT hook up a 12v battery unless you would like to fry your coil and blow all your fuses among other bad things.
It will run just fine without a battery period, battery is just to help out the lights and blinkers.
Did you check the timing at all? Not sure what that bike particularly calls for but a certain gap in the points is required before tdc to set the ignition timing properly.

All a bike needs to run is spark, fuel, compression and timing. You have spark you said, carbs are rebuilt you said so should have fuel, as long as the compression is good the timing is the thing to check.
 

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Discussion Starter · #3 ·
First things first that bike has a 6v system and takes a 6v battery so DO NOT hook up a 12v battery unless you would like to fry your coil and blow all your fuses among other bad things.
It will run just fine without a battery period, battery is just to help out the lights and blinkers.
Did you check the timing at all? Not sure what that bike particularly calls for but a certain gap in the points is required before tdc to set the ignition timing properly.

All a bike needs to run is spark, fuel, compression and timing. You have spark you said, carbs are rebuilt you said so should have fuel, as long as the compression is good the timing is the thing to check.

Thats kind of what i figured lol the 4 simple rules, did not know about the timing ill look that up, thank you very much, and the magneto is pretty much an alternator, pulled the plugs and theyre both soaked ... but its 11:41 now and i was up till 5 last night ... compression test and checking timing tomorrow thank you again
 

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sickboy
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No problem man, welcome to the forum, theres a wealth of knowledge on here to help ya out. Get back to us and let us know if ya get it figure out.
 

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Discussion Starter · #6 ·
What are the results of the compression test and how new/old is the fuel?
Brand new gas in tank/carb and havent done a compression test yet, i will tonight wheb i get home, anyone have any idea what it should hold? Ive read anywhere from 90psi to 135 psi
and just another question for electronics, if it does get running since all the electrical has been gutted, to convert to 12v do i just need a to make a new harness or will i need new instruments too? IE all the switches and tach/speedo

i read the factory 6v switches/gauges/magneto/coil will all hold enough power to convert ... any oppinions?
 

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sickboy
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Anywhere from 100-130psi should be just fine, if its under 100 you may want to start looking for a new top end.
As far as the 6v to 12v conversion I have no idea lol. Someone else will have to chime in on that, but I mean there is no cdi or ecm or anything like that so personally I would just run the 12v and replace the 6v bulbs as they blow.
 

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Discussion Starter · #8 ·
Anywhere from 100-130psi should be just fine, if its under 100 you may want to start looking for a new top end.
As far as the 6v to 12v conversion I have no idea lol. Someone else will have to chime in on that, but I mean there is no cdi or ecm or anything like that so personally I would just run the 12v and replace the 6v bulbs as they blow.
Well ... compression test result ... apparently i have weak legs lol got 30-32 psi. rings are fried, some of thegaskets were torn up, and ive got a bearing going bad(think its a crank bearing but it was 3:30 am and i had to be up at 7 lol and also, i measured the Inner Diameter of the cylinder amd it measured 70.26 mm so do i need a ring size of .25 oversize or .50
and as far as the lights/accessories, i have to re wire everything anyways ... 12v here we go
 

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sickboy
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Well ... compression test result ... apparently i have weak legs lol got 30-32 psi. rings are fried, some of thegaskets were torn up, and ive got a bearing going bad(think its a crank bearing but it was 3:30 am and i had to be up at 7 lol and also, i measured the Inner Diameter of the cylinder amd it measured 70.26 mm so do i need a ring size of .25 oversize or .50
and as far as the lights/accessories, i have to re wire everything anyways ... 12v here we go
If your bore measures 70.26 near the top id bet that the cylinder is quite out of round. Rings are going to cost ya $30 anyway so if I was you id bust out an extra 70 and just buy a .50 mm overbore piston kit and freshen up the whole top end. A bore job should only cost ya $40 or so.
 

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Discussion Starter · #10 ·
If your bore measures 70.26 near the top id bet that the cylinder is quite out of round. Rings are going to cost ya $30 anyway so if I was you id bust out an extra 70 and just buy a .50 mm overbore piston kit and freshen up the whole top end. A bore job should only cost ya $40 or so.
Thats exactly what im doing ... bigger motor for the win lol and i got to thinking about that 12v swap, i have read that the magneto needs rewound? But again also heard it could handle it, i also got to thinking, i know it produces electicity but does that mean it will chaerge the battery?
 

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sickboy
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Thats exactly what im doing ... bigger motor for the win lol and i got to thinking about that 12v swap, i have read that the magneto needs rewound? But again also heard it could handle it, i also got to thinking, i know it produces electicity but does that mean it will chaerge the battery?
Shouldnt really be much to it, I would doubt the stator would need to be rewound to produce the extra 6v needed but I could be wrong. That is easy enough to check though, just throw a multi meter on it. Its not really a "can handle it" type of thing. The stator would be just fine, the battery does not provide power to the stator, it is the other way around. The battery is charged by the stator threw the regulator/rectifier. The regulator/rectifier would need to be replaced with a 12v one (should be able to find one for $20-30). The stator (magneto) SHOULD put out much much more than the 6v the bike runs its lights and such on, it is the regulator/rectifier that transfers whatever voltage it receives from the stator coil to 6v and sends it to the battery. So if you just replace the reg/rect with a 12v one it should then send 12v to the battery instead of the 6.

BUT I do believe that bike has 2 different stator coils, one that feeds the battery/lights n stuff and another that just goes to power the ignition coils. If this is the case you may be able to just leave the one stock stator coil to power the ignition coils and rewire the other main stator coil to a 12v reg/rect to charge the battery and just run all your lights switched off of the battery.

make sense? lol
 

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Shouldnt really be much to it, I would doubt the stator would need to be rewound to produce the extra 6v needed but I could be wrong. That is easy enough to check though, just throw a multi meter on it. Its not really a "can handle it" type of thing. The stator would be just fine, the battery does not provide power to the stator, it is the other way around. The battery is charged by the stator threw the regulator/rectifier. The regulator/rectifier would need to be replaced with a 12v one (should be able to find one for $20-30). The stator (magneto) SHOULD put out much much more than the 6v the bike runs its lights and such on, it is the regulator/rectifier that transfers whatever voltage it receives from the stator coil to 6v and sends it to the battery. So if you just replace the reg/rect with a 12v one it should then send 12v to the battery instead of the 6.

BUT I do believe that bike has 2 different stator coils, one that feeds the battery/lights n stuff and another that just goes to power the ignition coils. If this is the case you may be able to just leave the one stock stator coil to power the ignition coils and rewire the other main stator coil to a 12v reg/rect to charge the battery and just run all your lights switched off of the battery.

make sense? lol
This does make sense but what about the condensers on the ignition system? Im not an electrician or anything but I dont think the 6V condensers will work? I would assume any condenser from an early 70's 12V bike will work, no?



I found a reg/rec from this post for my suzuki T350. Looks like you can get a 12V coil too.

http://www.suzuki2strokes.com/forum/viewtopic.php?f=29&t=4824

I dont know if you are thinking about eliminating the battery but most road bikes are unable to run without one. My YDS-3 (6V system) and T350 both need batteries to start and run since the battery supplies power to the coils upon start up. Since you have a little enduro you might be able to get away with it, but its a common misconception that all bikes will run without a battery.
 

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sickboy
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This does make sense but what about the condensers on the ignition system? Im not an electrician or anything but I dont think the 6V condensers will work? I would assume any condenser from an early 70's 12V bike will work, no?



I found a reg/rec from this post for my suzuki T350. Looks like you can get a 12V coil too.

http://www.suzuki2strokes.com/forum/viewtopic.php?f=29&t=4824

I dont know if you are thinking about eliminating the battery but most road bikes are unable to run without one. My YDS-3 (6V system) and T350 both need batteries to start and run since the battery supplies power to the coils upon start up. Since you have a little enduro you might be able to get away with it, but its a common misconception that all bikes will run without a battery.
Well i think the condensers are built into the stator plate itself on the dt250 but it shouldnt make a difference either way. All the condenser does is "soak up" the extra current/spark made when the points open and the magnetic field collapses. If you use a 12v reg/rect it will in no way change the amount of current ran threw the condenser from the points/stator coil so nothing should change as all of that takes place "in line" before the reg/rect and battery.

does that make sense? lol man its hard to type out stuff about electrical shit. It makes sense in my head but its hard to put electrical stuff in words sometimes haha.
 

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Discussion Starter · #15 · (Edited)
ok guys i was talking with a friend and he mentioned this ....
1.) the only wire right now coming out of the magneto is black straight to ignition coil, could i just as easily get a rectifier, and run as so

1.) magneto, to 2.)rectifier(to get 12v for the LEDs),3.inline 12v 30A fusable link 4.)ignition switch(to only get power through with a key) 5.) gauges/lights? 6.) ground to frame? or is this too much of a drawn out system?

recieved gasket set in the mail today, top end kit and bearings should be in by the end of the week ... shes about to come together
if i can figure out my lights :p
 

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sickboy
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Well isnt a condenser a capacitor? Too much voltage will make the capacitor to fail right? So if the capacitor is rated at a 6V system then 12V system would probably fry it or not produce a large enough charge to spark the coils?
Well the capacitor sends out power, it does not receive power, this is what the reg/rect is for. The magneto with the attached capacitor sends out AC power, which can obviously travel both ways. The AC power goes to the reg/rect which changes it to DC power which only runs one way. So having the reg/rect between the magneto and the battery means that the power from the battery can not get to the magneto only the opposite. Magneto and capacitor sends power to the battery and there is no way for the battery to send power the opposite way so should be no way to overpower the capacitors/condensers or any change in the way they function sense the magneto hasent changed at all. Only thing that would possibly fry them is if you rewound the magneto for more power.
 

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sickboy
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ok guys i was talking with a friend and he mentioned this ....
1.) the only wire right now coming out of the magneto is black straight to ignition coil, could i just as easily get a rectifier, and run as so

1.) magneto, to 2.)rectifier(to get 12v for the LEDs),3.inline 12v 30A fusable link 4.)ignition switch(to only get power through with a key) 5.) gauges/lights? 6.) ground to frame? or is this too much of a drawn out system?

recieved gasket set in the mail today, top end kit and bearings should be in by the end of the week ... shes about to come together
if i can figure out my lights :p
So there is only one wire coming out of the magneto right now? Should be as least 3 unless he was running no lights and no battery.

The way you wrote out to wire it up sounds fine to me.
 

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Discussion Starter · #18 ·
So there is only one wire coming out of the magneto right now? Should be as least 3 unless he was running no lights and no battery.

The way you wrote out to wire it up sounds fine to me.
Correct, i have to take it all apart anyways and look at it because the crank bearings bad, and like i said everything was in boxes lol, so the only wire on the bike was magneto to coil

Now my next question is ... since its converting to 12v am i going to have to run a 12v dc to 6v dc to get back to 6 before the magneto?

-- and was i correct in the wiring from coil to gauges will prevent a kickstart withought a key unless key is on?
 

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Discussion Starter · #19 · (Edited)
And also since im going to get a rectifier do i even have to have a battery?
 

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BLACK BELT
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You can run without a battery, but it sucks because your lights, blinkers, and horn will get brighter/louder as the rpms go up, and probably none will work when the bike is idling or at low rpms.
 
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