Author Topic: DOHC coils- which side is "+"? (Read 2579 times)

greddm · « **on:** February 15, 2014, 04:56:52 PM »

I've got a set of used DOHC (not sure the year) coils to use with my dyna-s ignition. I'm just not sure how I tell which spade goes to the ignition and which goes to power? Pic below.

1977 CB750

bjbuchanan · « **Reply #1 on:** February 15, 2014, 04:59:05 PM »

They don't have a positive or negative, that's why they aren't marked. These types of coils don't work like that

Just hook them up either way, making sure to have blue/yellow going to the correct set of points.

If they are DOHC coils they are gonna only be 3 ohm, use more current but don't get more oomph really. Just a thought

greddm · « **Reply #2 on:** February 15, 2014, 05:02:39 PM »

Thanks. I was told they were 5ohm. 3 will still work though right? I'm using them because I got them with a bunch of other parts, so trying to save $$$.

1977 CB750

dave500 · « **Reply #3 on:** February 15, 2014, 07:03:49 PM »

check them with a multimeter anyway?

thirsty 1 · « **Reply #4 on:** February 15, 2014, 07:13:10 PM »

Info

http://forums.sohc4.net/index.php?topic=67543.msg1458522#msg1458522

HondaMan · « **Reply #5 on:** February 15, 2014, 07:23:56 PM »

Quote from: greddm on February 15, 2014, 05:02:39 PM

Thanks. I was told they were 5ohm. 3 will still work though right? I'm using them because I got them with a bunch of other parts, so trying to save $$$.

1977 CB750

I'd sure recommend checking them with a meter. I don't think any DOHC coils were even 3 ohms, most were even less than that. This will toast your Dyna.

greddm · « **Reply #6 on:** February 15, 2014, 07:25:47 PM »

Do I connect the meter to the spades or the plug side?

1977 CB750

dave500 · « **Reply #7 on:** February 15, 2014, 07:31:48 PM »

the spades to determine the resistance ohms,the less resistance is like a higher wattage light bulb,itll pull more current,itll load what ever is powering it heavier.

greddm · « **Reply #8 on:** February 15, 2014, 07:37:54 PM »

So does this mean I've got 3ohm coils?

1977 CB750

dave500 · « **Reply #9 on:** February 15, 2014, 07:40:15 PM »

your meters internal battery is down,thats the "BAT"icon in the dispaly upper left,replace it first then recheck,a low meter battery can make them speak with forked tongue!

greddm · « **Reply #10 on:** February 15, 2014, 07:41:04 PM »

Ha ha, we'll do

1977 CB750

HondaMan · « **Reply #11 on:** February 15, 2014, 07:57:48 PM »

Also: digital meters have their own offset resistance in low Ohms range. So, after the new battery is in, touch those probes together and take the probes-only reading (likely around 0.5 ohm or so), and then SUBTRACT that number from your coil reading. You probably have 2.5 ohm coils there, which is typical of the DOHC systems using CDI ignition boxes. These are not a good coil for the SOHC4 bikes.

bjbuchanan · « **Reply #12 on:** February 15, 2014, 07:58:25 PM »

Quote from: dave500 on February 15, 2014, 07:40:15 PM

your meters internal battery is down,thats the "BAT"icon in the dispaly upper left,replace it first then recheck,a low meter battery can make them speak with forked tongue!

you catch the oddest stuff dave

greddm · « **Reply #13 on:** February 15, 2014, 08:01:40 PM »

Last time I buy a box of random crap from someone with only their word on what it is! Good news is that they were practically free. So for replacements should I go with 3 or 5 ohm dyna coils?

1977 CB750

dave500 · « **Reply #14 on:** February 15, 2014, 08:05:39 PM »

its attention to detail bjbuch,use what ever coils are recommended for the dyna system you have greddm,good reminder aswell hondaman,we often forget that!