Plug gap evo coil

[Reddog74usa]

I'm running points on my 68 FLH but replaced the original coil with one from a 96 Evo so do I set the plug gap at the evo or shovel settings? I'm thinking it's the coil that requires a specific gap as the points or electronic module only serve as triggers. Any info on this is appreciated.

[Burnout]

Try .045" I would not try any larger.

You can open the gap until it misfires, it will not hurt anything.

When the MoCo first introduced EI, they spec'd a plug gap of .060". I think a lot of folks had problems with a gap that big.

Yes the plug gap is determined by the amount of spark energy available from your coil.

A points coil has a 5 ohm primary, a stock EI coil has a primary resistance of 3 ohms. You should use an EI coil to take advantage of the electronics and get the higher spark energy output. Some Dyna coils have an even lower primary resistance.

[Racepres]

But... I would not recommend an EI coil with Points...
Use the correct "Potty mouth"...

[Reddog74usa]

Stock plug gap according to the manual for an Evo is 38 to 42 so I'm goin with 40. I have used EI coils on points iggys for many years without an issue so I'm goin for it but I think I'll grab a good points coil just in case.

[JW113]

Using a 3 ohm coil with points means you're about doubling the current through them. If that is working for ya, then good luck I guess.

Plug gap is related to how much high voltage breakover it takes to spark across the gap. The wider the gap, the more voltage required. The other thing that affects break over is air. A plug fires easily in a high or partial vacuum. When you open up full throttle and fill the cyl with air, it takes more voltage to fire the plug. Same with higher compression, more air molecules crammed in there for the spark to break through. This is why the older points ignitions with small plug gap in low compression engines could run fine on 10,000V coils. Today, it's more like 30,000V coils or more.

-JW

[Reddog74usa]

Thanks JW for the detailed info as to the difference and why it's better to run the points coil vs. the IE coil. I'm not fond of made in china crap parts and would appreciate any suggestions on a good quality points coil for the bike. Thanks, RD

[76shuvlinoff]

Dual plugged with 3 ohm coils I have them set at a tight .025 for years, but I am not running points.
.040 ought to be good for single plug systems.

[Ohio HD]

Dynotec DC7-1, 5 ohms, dual tower, dual fire system.

[rigidthumper]

Adding to what JW said- remember Ohms law? V=IR, R=V/I, I=V/R, V= volts, I= current, R= resistance.
V (12V system, usually has somewhere between 13.6-14.2 volts running)
R ( resistance of coil primary- 3 for electronic, 5 for points)
I is current flow( in amps) when circuit closed. Spark discharge occurs when circuit is broken.
Electronic coil 12V / 3Ω = 4A, more current flow, but the solid state components can endure this. Will pit points contacts rapidly.
Points coil 12V / 5Ω = 2.4A, so points coils use less amperage, so the contacts last longer ( less welding affect)
I've seen racing (nitro) setups with 1/2 Ω resistance, and dual batteries (24V system), and the plugs are gone by the end of the pass.

[Reddog74usa]

Thanks, Just picked up a coil on ebay. It's a 5 ohm by Andover a good quality MADE IN USA part. When I was going thru the search I found a NOS OEM coil from Harley in the original box with part number n all. When I zoomed  in to read the entire factory label it was right there MADE IN CHINA 

[JW113]

I run an American made Blue Streak 5 ohm coil on my '77. Always look for Blue Streak first for any ignition or electrical parts. Can't beat the quality, but not cheap either. Ya gits what ya pays for!

That said....

The Walmart mentality has essentially destroyed a vast amount of American and even European manufacturing. Having to buy parts that are made in China, in many cases, is not a choice but a reality. Very few world-wide OEMs don't use Chinese made parts. The thing you have to be aware of, there is high quality made in China, and then there is everything else. It all depends on the company that is designing/selling the parts, and how well they manage quality. Don't think that you can't find a well made coil that comes from China, you can. You just have to do the homework, and know who you are buying from.

-JW

[Reddog74usa]

I agree but I will buy USA or nothing at this point as I had an unfortunate incident about two weeks ago when a woman did a roll thru a stop sign causing me to hit the brakes real hard. The backing plate on my front drum brakes just broke apart snapping the mounting studs off that hold the shoes in place and even bent the stud that mounts near the fender mount. The damage that was done at just under 25 MPH was unbelievable. Upon checking out the parts when I took it apart I found that the backing plate was a made in china copy so screw made in china as it almost cost me my life. I have had nothing but issues with the china crap. I lost my front brakes totally and had to go into the oncoming traffic lane to avoid the crash and was lucky nothing was coming.

[kd]

Using a 3 ohm coil with points means you're about doubling the current through them. If that is working for ya, then good luck I guess.

Plug gap is related to how much high voltage breakover it takes to spark across the gap. The wider the gap, the more voltage required. The other thing that affects break over is air. A plug fires easily in a high or partial vacuum. When you open up full throttle and fill the cyl with air, it takes more voltage to fire the plug. Same with higher compression, more air molecules crammed in there for the spark to break through. This is why the older points ignitions with small plug gap in low compression engines could run fine on 10,000V coils. Today, it's more like 30,000V coils or more.

-JW

  Reducing the plug gap also lengthens the time the spark can hold across the gap and that compensates for high compression use. Cam timing can have an influence here too.  My plug gap on a 10.5:1 stroked shovel was .022 with points and a magneto.  I used the narrow gap to lengthen the time the spark held as / after the field collapsed.

[76shuvlinoff]

Does opening the gap retard the ignition?

[JW113]

Not really. If we are counting MICRO seconds for the coil field to collapse and raise the voltage higher to jump the gap, maybe. But in practical terms, it's in the noise.

-JW

[kd]

Opening the gap shortens the duration the spark holds hot and blue and collapses sooner.

[RTMike]

The more you open the plug gap the more power it takes to fire the plug.plug gap for a points ignition system is standard at .025 

[JW113]

It there a question there?

-JW

[Hillside Motorcycle]

Increased spark kernel intensity with a tighter gap.

[Hossamania]

I used to set my gaps at the maximum end of the range, thinking a "bigger" spark would work better, but read here some time ago that it takes more energy to bridge that gap causing a potentially weaker spark, and now set my gap at the minimum spec.

[Reddog74usa]

Same here Hoss. I did get the correct coil and will be setting the gap at the minimum.