1973 Hi-rider no spark

The resistive plug does absorb energy (ie voltage does drop across the resistive part) so the spark will not have as much energy.

If an ignition system is designed to use a resistive plug, the sparking energy will be what the designer wanted.
If an ignition system is designed to not use a resistive plug, and a resistive plug is used, the spark energy will be reduced.
I don't think it is reduced enough to significantly affect combustion.
(My personal guess is that a slightly weakened spark might not cause the flame front to start as quickly)
I hope there are others who will add their thoughts!

Dennis

Resistor plugs, used in old two-strokes would continue to fire when somewhat oil fouled, whereas a similar condition NON resistor plug would not. It was a boon to reliability.

concours said:

Resistor plugs, used in old two-strokes would continue to fire when somewhat oil fouled, whereas a similar condition NON resistor plug would not. It was a boon to reliability.

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I'm no engineer but one would think that it would be just the opposite. Anytime a resistance would be introduced into the energy path to create spark, there would be reduced energy for the plug to "jump the gap" to spark.

quawk said:

I'm no engineer but one would think that it would be just the opposite. Anytime a resistance would be introduced into the energy path to create spark, there would be reduced energy for the plug to "jump the gap" to spark.

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Just reporting some observations.
Starting old snowmobile engines at 0F before electronic ignitions and synthetic oil was more delicate a dance

NGK plugs sold on Ebay are often fakes. NGK knows about this and has produced a video detailing ways to spot fake versions of their spark plugs.
Not knowing this, I bought some fake NGKs on Ebay.
They weren't good fakes!

I'm not sure about Champion plugs on Ebay. They might be ok as I've read that the fakers only do NGK, because NGK is a premium brand.

I've had no real problem with authentic NGK however starting seems just a little easier with the Champion copper core plugs. That might be just my imagination. The switch to Champion seemed to make the 1 or 2 and occasionally 3 kick bike into a 1 kick every time bike.
I was able to order from Napa all of the Champion copper core non resistor plug types needed for the little herd here. I ordered some spares as well as things change and older style things become unavailable. Like ethanol free gas!

Glen

My commando was very difficult to start when I accidentally fitted suppressed plug caps and plugs
Once started it ran fine
This is with Lucas Rita ignition
I changed to none resister caps and everything is well

Way back in the 70's, Cook Nielson fitted K-Mart automotive coils to his points fired, Ducati 750 SS, for a better spark to go racing.
I've always assumed the intensity of the spark was coil based.
My question is this. Do the modern day E-ignitions amplify or intensify the spark?
Or is spark quality Coil based?

worntorn said:

I've used emery with mixed results. I'm back to using a points file now.
Too bad, as the folded emery seemed to do the job so nicely and easily.
The problem with emery is that most or possibly all Emery paper uses Alumimium Oxide for the grit material. Aluminium Oxide is a wonderful insulator.
After using Emery paper on my Vincent (Norton) points a few times I eventually made it into a hardstarter then a nonstarter.
The points file brought it back to life.

Glen

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These are a little more delicate on the contact surface. Also great on relays.
Pete

MichaelB said:

Way back in the 70's, Cook Nielson fitted K-Mart automotive coils to his points fired, Ducati 750 SS, for a better spark to go racing.
I've always assumed the intensity of the spark was coil based.
My question is this. Do the modern day E-ignitions amplify or intensify the spark?
Or is spark quality Coil based?

Click to expand...

The original Ducati coils were known to be very poor, to put it politely!
I've always regarded the spark as predominantly a function of the coil, plug & HT lead.
EIs come with coil voltage/resistance recommendations, which will obviously have an influence. Not that I've experimented much, except on a Ducati, of all things

Modern electronic ignition systems can significantly increase the spark energy.
(I am not saying always!)
You can read this when sometimes they recommend increasing the spark plug gap.

Transistor switching in electronic ignitions can take a lot more primary circuit current than a points type system
and spark energy is roughly proportional to primary current. So electronic systems can provide more spark energy

In addition electronic ignition increases the dwell time, the time during which current flows freely through the coil and this
can increase spark energy, especially at high rpm when the dwell time is not enough time for the coil to fully saturate

So replacing resistive spark plugs with non resistive can be the edge that gets our bikes to fire first or second kick!!

Dennis
Vancouver

DennisMo said:

The resistive plug does absorb energy (ie voltage does drop across the resistive part) so the spark will not have as much energy.

If an ignition system is designed to use a resistive plug, the sparking energy will be what the designer wanted.
If an ignition system is designed to not use a resistive plug, and a resistive plug is used, the spark energy will be reduced.
I don't think it is reduced enough to significantly affect combustion.
(My personal guess is that a slightly weakened spark might not cause the flame front to start as quickly)
I hope there are others who will add their thoughts!

Dennis

Click to expand...

The volage drop is approximately 0.25%. The voltage required to spark is less than the coil can provide so that drop means nothing. This is assuming a 0.025" plug gap, normal resistor plugs, normal temperatures, proper fuel/air mixture, and 8.5:1 compression ratio giving about a 2M ohm gap resistance.

I thought that the air gap resistance drops significantly once the spark starts to jump which ionizes the air...

Dennis

DennisMo said:

I thought that the air gap resistance drops significantly once the spark starts to jump which ionizes the air...

Dennis

Click to expand...

Once the spark starts, you don’t have much to worry about.

marshg246 said:

The volage drop is approximately 0.25%. The voltage required to spark is less than the coil can provide so that drop means nothing. This is assuming a 0.025" plug gap, normal resistor plugs, normal temperatures, proper fuel/air mixture, and 8.5:1 compression ratio giving about a 2M ohm gap resistance.

Click to expand...

DennisMo said:

I thought that the air gap resistance drops significantly once the spark starts to jump which ionizes the air...

Dennis

Click to expand...

Since current is flowing - let's say for the fun of it that the voltage required to start the current flowing across the gap is 12,000 volts. I=E/R so 12,000/2,005000 to start. So the initial current is about .006 amps. Now let's say that the effective resistance drops to 1M ohm once the current is flowing, so 12,000/1,005000 means that the current is now .12 amps. So the voltage across the resistor and gap are (E=IR):

Before: .006*5,000 = about 30 volts and the voltage across the gap .006/2,000,000 is about 12,000 volts - the coil voltage is 12,030 volts
During: .012*5,000 = about 60 volts and the voltage across the gap .012/1,000,000 is about 12,000 volts - the coil voltage is 12,060 volts

You know the plain old Lucas coils are capable of high voltage - the bike will run at high or low altitude, at as least 13:1 compression ratio, rich or lean, and even at the Norton top gap of .028". They probably won't spark standard plugs at a wider gap or even higher compression.

Any way you look at it the voltage across the plug gap will remain the same. If yo umake a coil that can produce a million volts, the volts across the gap won't change. When you have fancy plugs like surface gap, they has much higher resistance and therefore require a coil with higher capability.

Of course I'm using steady state numbers. A coil secondary collapsing is not like steady state - for one the voltage and therefore current ramps up and ramps down - it's like a flat-top spike and the it, to a much lesser degree goes the other way.

Current update on progress of my recently acquired 1973 750 Hi-Rider. I can now consistently get her to start and run, sometimes (with fingers crossed) on the first kick. While running a couple of oil leaks showed up, which have now been corrected. Even though it will start and run, it just isn't running as smoothly as I'm sure it's supposed to. Lowered the idle speed some and would still continue to run, but when I try to tweak the air/fuel mixture screw, it just doesn't seem to improve or change much. As I've posted earlier, carbs have been off, run through the ultrasonic and cleaned. As others have suggested, I've went back and ran a .016" wire through the mix screw "bush". Have just done a compression check. Used a good quality Milton compression tester. Throttle cranked open while kicking. Kicked through 7-8 times on each test. Right side will show 170 p.s.i., and the left side will show 180-185 p.s.i. Test results would repeat on multiple testings. This seems like "very" good compression. Had installed new correct number plugs, (Chanmpion N-7Y) befor starting to try to tune the bike. When plugs were pulled, they look black/sooty. I realize, in general this means rich. Any suggestions, offhand, on what direction to go from here?

Assumptions: Carb's pilot circuits are completely clean from the bottom of the bowl to the two tiny holes in the bottom of throat. Carbs are not worn out. Fuel height is the same in both bowls, jets are clean, needle clips are in the same slot both sides. Timing is between 28 and 32 degrees. Running E10 gasoline.

Do this exactly and it will start and idle at about 700 and will idle at 1100 when warm: https://gregmarsh.com/MC/CarbSync.aspx

No, this is absolutely not the book method, and it is not how most do it.

quawk said:

but when I try to tweak the air/fuel mixture screw, it just doesn't seem to improve or change much.

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A 16 thou wire will push the dirt back into the pilot gallery, when you then use the carb the dirt comes back forward and the pilot jet gets clogged again. Use a #78 which is a 16 thou drill and the dirt is collected in the drill flutes and taken away when the drill is removed. In the venturi on the engine side of the needle are 2 small holes where the pilot mixture is introduced, these need to be probed and cleared too. When you adjust the pilot mixture screw and the engine does not respond the pilot system is not working.

I have a mikuni and when I bought the bike, I had idle mixture problems several times whereby the bike starts to idle
poorly. The problem is that deposits build up from the gas where the idle mixture is bled into the main circuit.

The cause was due to the bike being stored previously.

The solution I finally figured out was to take out ther idle screw (not the carb which I did a few times), inject carb cleaner
into the idle passage several times over a few minutes, then blow out idle passage with air.

I am not sure what fluid is in your ultra sonic cleaner, but suggest you try the above!

Dennis
Vancouver

You can have the pilot jet (bush), the two tiny holes, the passage to the back of the carb all open and clean and still not have a working pilot circuit.

The pilot circuit starts at the bottom of the float bowl. Goes up through one of the two passages integral to the bowl, meets the bottom of the carb and make a sharper then 90 degree turn to a passage through the bottom of the carb body, then makes a 90 turn towards the center. Sounds like from there you might be clean but that passage in the bottom of the carb body often gets clogged when a bike sites. Carb cleaner and ultrasonic cleaners often won't break through. Usually a wire will crack it loose and then the cleaner will work, but don't blow from the bottom of the carb as it will pack against the jet.

marshg246 said:

You can have the pilot jet (bush), the two tiny holes, the passage to the back of the carb all open and clean and still not have a working pilot circuit.

The pilot circuit starts at the bottom of the float bowl. Goes up through one of the two passages integral to the bowl, meets the bottom of the carb and make a sharper then 90 degree turn to a passage through the bottom of the carb body, then makes a 90 turn towards the center. Sounds like from there you might be clean but that passage in the bottom of the carb body often gets clogged when a bike sites. Carb cleaner and ultrasonic cleaners often won't break through. Usually a wire will crack it loose and then the cleaner will work, but don't blow from the bottom of the carb as it will pack against the jet.

Click to expand...

Thanks for the response and advice. Will be doing some more investigation and cleaning on the carbs. This bike did "sit" for many years. When removed and disassembled, one carb looked very cleaned, but the other one looked very crusty.