Yamaha DT 250 1974-75-76

[dsm6678]

Yamaha DT 250 1974,1975,1976

Source Coil part number 438-81312-20-00

Does anybody know the resistance for the Source coil on this motorcycle and how to check it. I would think I would take the magneto cover off and check both ends of the coil or can I just check it from the wiring harness to ground? The problem is I do not know the resistance it is supposed to have. Has anybody checked their source coil or do you know what the ohms are supposed to be? I cannot find it in the factory book or the clymer book!

Thanks,

Darren

[dsm6678]

I cannot believe I found it. It was at the bottom of a parts list here http://www.motogrid.com/pages/parts/viewbybrand/2/yamaha.aspx

It is supposed to be 1.65 ohms.

What is the best way to test that? I think I should just check the coil wire at both ends?

[Airhead]

I cannot believe I found it. It was at the bottom of a parts list here http://www.motogrid.com/pages/parts/viewbybrand/7/honda.aspx.

It is supposed to be 1.65 ohms.

What is the best way to test that? I think I should just check the coil wire at both ends?

I did find this myself, your link doesnt work by the way but i have posted access to the manuals in the 'Workshop' forum.

Somehow i cant quite get how that figure is so much different to the DT400 which is also listed.

...Paul

[dsm6678]

I did find this myself, your link doesnt work by the way but i have posted access to the manuals in the 'Workshop' forum.

Somehow i cant quite get how that figure is so much different to the DT400 which is also listed.

...Paul

I fixed that link, That was strange. It makes no sense to me why the figure is so much different between The DT 250 and DT 400 source coil ohms. I wish I knew. What about the lighing coils they are different just look at them. The DT 400 has some type of extra coil attached to the lighting/charge coil. One more thing is that the yamaha diagrams are saying the DT 250 uses 30 watt headlight and the DT 400 uses 35 watt headlight but guess what my factory Yamaha manual says they are both supposed to use 35 watt headlights in 1975.

[Airhead]

I fixed that link, That was strange. It makes no sense to me why the figure is so much different between The DT 250 and DT 400 source coil ohms. I wish I knew. What about the lighing coils they are different just look at them. The DT 400 has some type of extra coil attached to the lighting/charge coil. One more thing is that the yamaha diagrams are saying the DT 250 uses 30 watt headlight and the DT 400 uses 35 watt headlight but guess what my factory Yamaha manual says they are both supposed to use 35 watt headlights in 1975.

Dont be surprised if you find thats its 165 ohms, it could be an error in the manuals, just measure between ground and whichever wire goes to that coil.

[Speedshop]

I manufacture ignition units for the SRs and XTs. What you find is they alter the 'front end' of the box to stop other boxes working with other generators. Its done to protect their business! They indtroduce a fudge factor to ensure the Cdi box from a SR500 won't work properly on a DT, for example. Actually the SR had 3 different CDI boxes over the years. They are all exactly the same, but have a different fudge factor applied so a 1978 model won't run a 83 box!

I.65 sounds low for this type of system. Something around 20 would be average - but then again it depends on what they did to get the box specific to that model!

[dsm6678]

Dont be surprised if you find thats its 165 ohms, it could be an error in the manuals, just measure between ground and whichever wire goes to that coil.

I checked it and I am getting .4 to .6 ohms. I bet that could possibly do something bad to the ignition coil, like burn it out because I already burned one out with this new source coil hooked up, although the ignition coil was old and used so I am not 100% sure but the more testing I do and the more feedback I here from people I am thinking the worst. I asked the guy that rewound my source coil if it was rewound wrong could it be possible to actually burn out an ignition coil. His answer was "Highly doubtful, you would have to have used a couple guages thicker wire than the original wire for that to happen" The problem is is that I think he did use to thicker wire. He did not mention number of turns so I am worried he did not pay attention to the number of turns and plus he should have check the resistance when he was done to see that it was at least close. I just bought a new ignition coil from Yamaha and it cost me over $70.00 I do not want to mess that one up to.

My lighting coil is also all messed up and he rewound that one to. I blew my headlight and indicator lgihts out and the battery is not charging, a new headligh cost about $58.00. I wish I found this website here http://www.smiffy.com/gary/512coil.htm this is the same lighting/charge coil in my motorcycle and I could have most likely rewound it myslef becasue I have done a pulser coil and was successful but I could not understand this lighting coil becasue it has two "take off's" throughout the coil windings and I had no idea how they attached or how they work but now I do. O yea I am getting infinite resistance from the charging wires, that is bad!

I am not mad at the company that did this well just not yet anyway lets see if they help me or just not care and keep my money. I do not think I can fight for the money because I just have the worst luck with things like this and my credit card company is going to start to think I have some type of problem or something. I think this will be the third time withing a year I was slighted purposely or not. O yea it cost me $150.00 to get the coils rewound.

I hope I can take it out one the trail this year hahahahah

[dsm6678]

I manufacture ignition units for the SRs and XTs. What you find is they alter the 'front end' of the box to stop other boxes working with other generators. Its done to protect their business! They indtroduce a fudge factor to ensure the Cdi box from a SR500 won't work properly on a DT, for example. Actually the SR had 3 different CDI boxes over the years. They are all exactly the same, but have a different fudge factor applied so a 1978 model won't run a 83 box!

I.65 sounds low for this type of system. Something around 20 would be average - but then again it depends on what they did to get the box specific to that model!

Interesting thanks for that information! Just one thing I forgot to add is that this system is not CDI it is points and condensor so it does not have a "box"

Thanks again.

P.S. I e-mailed a couple of what I would call experts on coils and let me see what they say. If they sound like they know what they are talking about I think it would be a good idea to post their responses on here to help out anybody with a problem with a source coil in the future.

[dsm6678]

I manufacture ignition units for the SRs and XTs. What you find is they alter the 'front end' of the box to stop other boxes working with other generators. Its done to protect their business! They indtroduce a fudge factor to ensure the Cdi box from a SR500 won't work properly on a DT, for example. Actually the SR had 3 different CDI boxes over the years. They are all exactly the same, but have a different fudge factor applied so a 1978 model won't run a 83 box!

I.65 sounds low for this type of system. Something around 20 would be average - but then again it depends on what they did to get the box specific to that model!

As for the different CDI boxes and source coils and pulsers I would think they would save money if they made them so they could fit more then just a couple of years and a few motorcycles. What you are saying is that it will be harder or less cost effective for an aftermarket manufacturer to make a cdi box, source coil, pulser coil, etc. if they keep changing them all the time?

[Speedshop]

Interesting thanks for that information! Just one thing I forgot to add is that this system is not CDI it is points and condensor so it does not have a "box"

Thanks again.

P.S. I e-mailed a couple of what I would call experts on coils and let me see what they say. If they sound like they know what they are talking about I think it would be a good idea to post their responses on here to help out anybody with a problem with a source coil in the future.

DOH! You mean the magneto coil! Right I don't have the DT info with me.......but the points XT500 generator i do have! This has a similiar set up as the POINTS DT with sepearte magneto and lighting/charging coils. while it will be different, 1.65 ohms seems in the ball park for a magneto coil (the XT500 is 2.25).

DSM6678- if one cdi box fitted all they wouldn't sell any new CDi units at full retail price plus it would make life easy for the after market manufacturers who would produce at much lower costs then OEM, so they ensure retails orders for the next 10 years (or however long they decide to carry on manufacturing for) by making them model specific. The differences are subtle and the basic PCB will be the same for hunderds of different models. The ND 70000 series is fitted to many bikes, but one version wouldn't run on other models due to minor component swaps - making a 1,000 units with a 100 ohm resistor in slot 'A' then 1,000 with a 750 ohm resistor in slot 'B' in a continuous 2,000 unit run is no big issue on an automated assembly machine.