Ural (boxer engine) points ignition.

[n3303j]

So I've got about 90K kilometers on the old Ural. I've just had my 4th electronic (modern) ignition go wonky. The heat under the front cover is too much for the electronics and they shut down on hot days forcing me to ride with the cover off. This is not acceptable. They eventually die. This is even less acceptable.

2007 750cc engine in the beastie.

So I ordered up a points system and centrifugal advance to replace all the delicate crap (original Russian parts that will bolt up).

It was suggested that I run a 5 Ohm primary coil with the points.
Easy enough as Dynatec makes a dual fire 5 ohm coil (for HD with points).

I will install a 5 Ohm dual fire coil with waste spark (worked for BMW).

Now I did a bunch of reading on points ignition vehicles and every article recommends a BALLAST RESISTOR in the circuit to reduce current flow through the coil while running. Coil gets 12 volts direct feed in start position and feeds through the ballast resistor while running. Easy enough with a tap off the starter solenoid.

So I got curious and pulled out my T3 wiring diagram and can't find any ballast resistor in that system. So I guess it's not imperative to have one.

Guzzi points are operating a single coil/plug each. I've gotten 70,000 miles out of the originals so far.

So I'm wondering if running a 5 ohm dual fire setup will last at least half that long or if I really should consider a ballast resistor? Looking for suggestions.

Off hand anyone know the primary resistance of a stock T3 coil?

[Rusty goose]

I ran my points on my Ural (650) and used a Harley dual lead coil as well. I did not use a ballast resistor and many many trouble free easy starting km's.  I switched for the same reason too, heat kept cooking the original Russian coil.

[Tom H]

T3 S/B 3ohm.

What a rabbit hole you can go down understanding coils.

Tom

[Aaron D.]

Ballast isn't needed. Certainly not with 5 ohm coils.

[Ratso88]

I'm running the original Soviet points with an air cooled VW condenser in my Dnepr with a dual fire Harley type coil.
No issues last 17 years. Will usually start on the first kick even in minus temps.

No ballast resistor in my set up.

I'd think you'd be fine without one.

[Chuck in Indiana]

I put a ballast resistor on the AeroLario. It started fouling plugs. Took it off and it's been fine ever since..

[berniebee]

I've always wondered why some vehicles have ballast resistors but not others. Btw, my '74 Plymouth Scamp had an electronic ignition with a ballast resistor, and none of my old electric start Japanese points ignition bikes had one. I've got two theoretical reasons as to why my bikes never had them: The additional cost and the lack of space to install a hot resistor.

The ballast resistor idea is good. During starting, the starter motor is drawing a lot of current which pulls the battery voltage lower. The coil might see only 7-9 volts. And the engine might be cold so combustion is not optimum. That's when you want the coil highly energized for maximum spark, so the ballast resistor is bypassed. When running, the alternator keeps the battery voltage at 14.5 volts, so the ballast resistor is placed in series with the coil to keep if from overheating. An ignition system designed without a ballast resistor (or some other voltage dropping circuit.) is necessarily a poor compromise. The coil has to be designed to start the engine under the worst (Weak battery, cold weather.) conditions, so guess what. Without a ballast resistor, your coils are running hotter than they need to be. Hotter temps = shorter coil life.  Getting back to my seventies Jap bike coils, they almost all had a reputation for "poor performance" and high failure rate. Well, duh, without a ballast resistor system, they just couldn't be very good.

So the answer is yes.  Especially if your coil is running hot, a ballast resistor is probably a good idea. But installing a too high value ballast resistor may result in a missing-under-load bike.  You'll have to play a bit with the value, so that your bike runs well under all conditions.  Most car parts stores (in the USA/Canada) have a good selection. I've got Dyna coils on my project, which supposedly run quite hot. I'll definitely be experimenting with a ballast resistor, once my puppy is up and running.   

[Alfetta]

what i recall is that on multi cylinder engines, such as a V8, operating from a single coil, produces very high charge-discharge rates and thus heat up the coil.
ballast resistors are not required if the coil remains within its operational temp range. engine mounted coils might also require a resistor.

It's a function of heat.

[Stretch]

"what i recall is that on multi cylinder engines, such as a V8, operating from a single coil, produces very high charge-discharge rates and thus heat up the coil."

I was wondering if that might be a factor.....

                                         -Stretch