General question about coil resistance

[rothfm]

Thought id ask the brite folks here as it is my home forum, just for general info if possible. This is a 1997 6hp.

Ive got a post on another forum for the mfg of this motor(not omc)...and getting a bit of guidance.

Would you guys know if i had 2x the spec resistance on the hi volt-side of the coil..,,could that result in intermittant spark....meaning one pull shows spark, then the next doesnt, then it will etc....

All things are clean and tight.

Im getting a dva but my resistance on stator charge and what they call pulsar coils is good.

Ita a single unit dual lead coil. When i pull cord, i get spark, when i pull again i dont(either lead).

Accross the plug wire boots should be 2800 to 4200ohms. I got 8900.

Prev owner has a new coil on it. No markings. So no idea if its correct.

In typing this im answering my own question i believe!!!

Was wondering if this higher resistance scenerio would exhibit what im seeing?

Ill be getting my dva soon

 

[bwkre]

Never seen a double unit as you describe but could it be 28-42 hundred ohms from either boot to common? That would explain the double reading as each coil would share the same common. Also be sure not to touch the probe tips while testing as it will slew high resistance readings.

 

[F_R]

I must confess I am not familiar with your 1997 motor (too new for me), but I believe bwke has probably already said it. I seriously doubt the secondary windings should be ohmed plug wire to plug wire. More reasonable would be plug wire to ground. If we are correct, that would explain your double resistance result. I haven't seen a double ended coil (plug wire to plug wire) since the 1940's. In such a setup, both plugs fire at the same time. So....it is possible, but I so seriously doubt they have resurrected that old system.

 

[gm280]

I'll have to add that IF your motor is a 4 cycle, then it would explain the every other sparking action. However if it is actually a 2 cycle engine, there is no way it can't spark every turn. And I also concur with the above posted comments about reading from one plug wire to ground and not across the two plug wires.

 

[racerone]

On most 2 cylinder 4 stroke motors the coils both fire at the same time and each revolution, one is on the exhaust stroke and is called a " wasted spark " system.

 

[bruceb58]

On most 2 cylinder 4 stroke motors the coils both fire at the same time and each revolution, one is on the exhaust stroke and is called a " wasted spark " system.

Even my Lexus and Harley have wasted spark systems....very common especially with engines that have coil over plug designs.

 

[rothfm]

Yes, this is true from what I learned...Both are meant to spark at the same time. One Piston will be at top, one at bottom...Ie...one spark is "wasted".

I called CDI, and they provided an updated printout of the resistance measurements as well as DVA Readings. Wire cap1 to wire cap2 should be 2800-4200 or so. Doesnt matter if coil is connected to anything or not. I get 8900.

All other resistance checks seem to be ok. CDI said when the DVA comes in take readings on Stator charge, and what they call the Pulsar(trigger)...If good, and the smaller Primary incoming Orange and black Coil leads are reading Volts in Spec...the CDI is good and to look further at Coil.

I thought the higher then expected resistance on the dual hi tension plug ends was my culprit. BUT LOW AND BEHOLD...I get home from work, and pull....Got spark on both and it seems to be staying.

Who knows...I'll keep pulling and testing..If it holds I'll get some fuel and see if this thing will start.

Picked it up for 100 bucks...incredible for a almost new condition 6hp (yamaha), As long as this Spark issue gets resolved. I will get a DVA soon.

Thanks for Humoring me...I'll post results in case anyone is wondering too.

 

[F_R]

I can't help but wonder if you are expecting too much(?). Are you using the correct spark gap to test? Are the electrodes sharp pointed? Does it make a difference how fast you pull it?

Very interesting what you found out about the coil. To me it looks like an ordinary CD system that has been used for years, but with two coils mounted on the same bracket. Guess I was wrong.

 

[boobie]

Maybe I missed it, but who manufactured this motor ???? Is it two or four stroke ????

 

[rothfm]

Hey boobie,

I had this out on the other MFG forum here on iboats, but wanted to get some other perspectives about coil measurements.

2 stroke yamaha 6hp.... More interested in seeing if that higher than expected resistance would make it spark, then not, then spark.

Anyway...For unknown reasons-at least tonight it is sparking when I'm pulling. Its laying down vs Upgright. Tomorrow I'll try it again in diff positions...Dunno. But its sparking as it should. I'll fuel it and try to fire it up also tomorrow.

Least I learned a bit more about ignition systems, always a good thing. That Dual "waste" spark kinda threw me off.


Thanks

mark

 

[F_R]

So, are you connecting both coil leads to a spark gap? Or at least grounding one and spark gap the other one? You can't just let one dangle in open air. There has to be a complete flow path for the electricity. At least that's the way it was back in the 1940s. What does Yamaha say? Inquiring minds here would like to know. I'd also like to know if it actually has two secondary windings on a common primary, or if it is one double-ended secondary. Testing plug wire-to-plug wire seems to indicate a double-ended secondary. This kind of stuff interests me.

 

[rothfm]

Exactly it. Its a double ended secondary with 2 hardwired plug wires off a single internal winding. Common single primay winding.

I kept an inline spark checker on one at a time with each plug in place- grounded.

Cdi states the secondary side spec for resistance of that internal winding is read from plug cap to plug cap.

Even though for the moment i have spark finally, my higher reading makes me think the PO has an incorrect coil in there as its not marked at all. Even the primary input resistance is off a bit. It looks like its brand new as he was trying to fix something and maybe got the wrong coil maybe.

Later today if it still has spark i will attempt to fire it up. I have a dva onway too.

Thanks all. Got me to thinking. Im so ised to my old crossflows-this was a bit different

 

[F_R]

Thanks for the information. I understand how it works, but was a bit surprised. Nothing new under the sun, I guess.

Just thinking though, your intermittent spark could be because of a fault with the connected spark plug at the opposite side. Remember, the spark has to jump that gap at the same time as the one you are checking. But then there is the problem with the funky resistance result. Sure sounds suspicious, doesn't it?

 

[rothfm]

Yea the measurment sure does.

Thanks. After work if spark still present will try to start. See whats next