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Discussion Starter #1
I've been reading about this mod for a year ( I've done it ) and still don't get the theory about solving hot start problems. You need ignition,fuel,and air for an engine to fire. You go out in the morning, set the choke ( fuel enricher ) and the bike starts right up. You ride for a while and shut down the engine. Now it is hard to start. What changed? The AIR, no. The IGNITION,no. The FUEL, YES. The density of the fuel changed. It is now more vaporized. It seems to me the hot start problem is only fuel related. I can see where changing the air gap helps in some ways but not in helping hot starts. Ok, I'll listen.
 

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My understanding is that it is in fact an Ignition issue.


90% of the hot start problems are cured by just installing a new AGM battery. So what's that saying?

Fuel density does not seem to play a part.... You can have a hot engine on a very cold day. Remember hot fuel is supposed to ignite easier than cold fuel anyway.

Not an electrical guru, so I too am not sure why decreasing the gap at the pickups is supposed to help, but would guess you get a higher trigger voltage and that helps insure a better spark.
 

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Sparky!!!
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changing the air gap in the pick-up coils actually changes the ignition curve, kind of like rotating the distributor on a car. you are advancing the timing just a fraction of a degree, so I am not sure why this helps... now the Coil Relay mod.... this one I do understand, by delivering a full battery charge to the ignition coils would make cold and hot starts easier as per KM's reply.
 

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Discussion Starter #4
My understanding is that it is in fact an Ignition issue.


" 90% of the hot start problems are cured by just installing a new AGM battery. So what's that saying? "

Not much. A new battery as opposed to an old battery will improve starting hot, cold, or in between. If there is adequate ignition to start the bike cold then there should be adequate power to start it hot.
 

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I won't even begin to say that I know why it would help hot starts, but I will say that for me it just did.
I would assume a smaller gap provides a stronger signal....which could provide a stronger spark???

All I know is that once I did the mod the hot start problem went away....and that was before I had an AGM battery and I did not have the iridium plugs in at that time.
 

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Discussion Starter #6
changing the air gap in the pick-up coils actually changes the ignition curve, kind of like rotating the distributor on a car. you are advancing the timing just a fraction of a degree, so I am not sure why this helps... now the Coil Relay mod.... this one I do understand, by delivering a full battery charge to the ignition coils would make cold and hot starts easier as per KM's reply.
Have to disagree. The ignition timing cannot be advanced or retarded on our bikes. Moving the pick up coil from a setting of .035 to .020 only reduces the distance the spark has to travel and the time it would take for it to do so. This would be related to changing the dwell on a system with points, but on that type system, you can rotate the distributor to advance or retard the timing.
I'm still listening
 

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My understanding is that it is in fact an Ignition issue.


" 90% of the hot start problems are cured by just installing a new AGM battery. So what's that saying? "

Not much. A new battery as opposed to an old battery will improve starting hot, cold, or in between. If there is adequate ignition to start the bike cold then there should be adequate power to start it hot.


Uh, not in the Vulcans case. Electronic parts don't work as well when hot, so really not sure if it's the JB, the ignitor or what.

It could be just a matter of technique... Which kinda hints at just a poor fuel mix from the carb when you're not using the choke.

As I said it was just "my understanding" from everything I've read over the years that hard starting when hot was an electrical issue.

You can offer any theory you want too... But given the results gained by just switching batteries at least my theory offers some tangible proof.

Perhaps those that have rejected their bike can stick an old wet cell back in and see if there's a difference??
 

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I believe that once the ignitor "warms up" the resistance in the control circuit increases, changing the operation of the ignitor slightly. I also believe you can get the ignitor to fire sooner by moving the pickup closer, hence "advancing" the timing. The magnetic field increases with the square of the distance from it, therefore the pickup coil should send a pulse sooner....
 

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You can offer any theory you want too... But given the results gained by just switching batteries at least my theory offers some tangible proof.
If you buy a new fully charged wet cell, that might also make the bike hot start easier.

Temperature is the culprit, right?
Where's the biggest temperature swing, inside the engine.

Here's some physics:

Permanent magnets loose flux density as heat increases.
Heat also lowers the permeability of Air.
It takes a higher flux density to excite a heated coil.
Inductance of a coil increases with heat.

So ...

Add all this physics up, and a moderately performing battery may not spin the motor fast enough to get a strong enough pulse from a more inductive coil in a less permeable environment from a weak flux density generated from .030"+ distance.

By moving the pickup coils closer to the magnet, you compensate for the negative changes in flux density due to temperature ... maybe ... just sayin'.

And the closer you get to the passing magnet, the sooner the pulse reaches trigger level. This would effectively advance the trigger, therefore, the ignition.

Of course, this is all just my opinion. except for the physics parts.

~~C8>
 

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Sparky!!!
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actually moving the pickup coils does in fact retard and advance he ignition... if you move the coils one way the rotor sends the signal a millisecond sooner (advancing the timing) and moving the coils the other way makes the coils sense the trigger later, thus retarding the ignition curve... I have messed with the pick up coils a lot... to find the optimal place to set them... Also, the Pickup coils do not spark...it is just a fancy magnet.

The pulser coil is a very simple component. It is generally housed in a small plastic container, and internally potted with epoxy or some other oil resistant material. The pulser coil itself is made up of a small magnet (the exposed metal you can see on the front of the housing), which is wound with a coil of very fine wire. The pulser coil may have one or two wires exiting the case to connect to the ignition box. On one wire systems, on side of the internal coil is grounded to chassis ground through the mounting hardware. On two wire systems, a wire from each side of the coil exits the case to connect to the ignition box.

The pulser coil generates it's timing pulse with help from the flywheel (Refer to the illustration above). The outside diameter of the flywheel has at least one timing mark, which consists of a raised ridge, spanning some percentage of the outer edge of the flywheel. This ridge is pronounced, and has sharp leading and trailing edges. The Pulser Coil is mounted to the engine sidecase in very close proximity (some thousands of an inch) to the flywheel, spaced to be extremely close to the timing ridge(s). The timing ridge is referenced to the Top-Dead-Center (TDC) piston location inside the engine. As the timing ridge on the flywheel spins past the pulser coil, the timing signal is generated. The leading and trailing edges of the raised metal ridge produce a low current, high voltage pulse, either positive then negative polarity, or negative then positive, depending on the direction of the coil winding inside the pulser coil. The ignition box then uses this signal to reference the piston location, and given it's inputs (RPM and TPS) it will determine the correct time to fire the spark plug, by discharging the internal capacitor out to the ignition coil, and finally the spark plug.


so your theory on making a hotter spark is incorrect. as Ron/Lance explained it to me, moving the pickup coils closer to the flywheel advances the timing a degree or so. no go to basic automotive distributors for a minute... when the engine is off, the counter weights are at rest to advance the timing slightly to help in starting the engine, as soon as the engine starts turning at a given rpm, the weights then spread out to retard the timing back to normal to prevent pre-detonation.

Kawasaki set the pickup coils retarded to help pass emissions.
 

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Discussion Starter #11
actually moving the pickup coils does in fact retard and advance he ignition... if you move the coils one way the rotor sends the signal a millisecond sooner (advancing the timing) and moving the coils the other way makes the coils sense the trigger later, thus retarding the ignition curve... I have messed with the pick up coils a lot... to find the optimal place to set them... Also, the Pickup coils do not spark...it is just a fancy magnet.

http://racetechelectric.com/ft-752-pulser-coil-ignition-systems.html

so your theory on making a hotter spark is incorrect. as Ron/Lance explained it to me, moving the pickup coils closer to the flywheel advances the timing a degree or so. no go to basic automotive distributors for a minute... when the engine is off, the counter weights are at rest to advance the timing slightly to help in starting the engine, as soon as the engine starts turning at a given rpm, the weights then spread out to retard the timing back to normal to prevent pre-detonation.

Kawasaki set the pickup coils retarded to help pass emissions.
You are correct about the " spark". I should have said pulse signal. I'm still digesting all the other info. Starting to make a little sense but still not totally buying it.
 

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#1 Electrical systems get less efficient as they get hot.
#2 It takes significant voltage/power to fire the ignition.
#3 As the starter cranks, it drops the battery voltage, resulting in less efficient ignition.

I have a friend with a bike that had a questionable battery. It would crank over but not spark. Once he installed a new battery, it started just fine.

The quality of motorcycle batteries is all over the map. Buy a cheap battery, and the voltage to the ignition can drop to where it won't reliably fire. Install a good battery, and the ignition will have more voltage to work with.

The pickup/coil gap works is electromagnetic in nature. The closer the coil/magnet are together, the stronger the signal. The strength of this signal varies with the inverse square of the distance. Closing a gap from 0.060" to 0.020" is HUGE. It might fire okay at 0.060", but the signal will be a TON more reliable at 0.020"!

Simply closing gap could in theory, slightly alter the timing, but it's only a fraction of a degree. It's not significant. The best thing to be gained from this, is a more reliable signal.
 

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You are correct about the " spark". I should have said pulse signal. I'm still digesting all the other info. Starting to make a little sense but still not totally buying it.
I'll weigh in on this one,in order to understand how it advances the timing you have to understand inductance and how a magnetic field is shaped and you also have to realize that this magnetic field rotates around with the rotor and the ingnitor passes through it every revolution of the engine. By moving the stock ignitor coils further into the middle of the field two things happen .1.The ignitor enters the magnetic field sooner and stay in it longer.2. it is in a stronger part of the field.

In theory, the coil in the ignitor is starting to make voltage sooner and all other things considered it should make a higher peak voltage and not drop off as fast as it would in the stock location.In practical application ,this indicates to me you should not only get an earlier,but also a stronger and longer pulse to the ignition coils before the magnetic field collapses and the ignitor is no longer sending a signal to them.

I think this also relates to ignition timing and length of time the coil is discharging power to the spark plugs.Resulting in a longer burn in the cylinder,no matter temperature,without factoring in the effect of ambient temperature on the coils in the ignitor.

Longer stronger spark should always make for a more complete burn and improve starting,The reason it seems to affect hot starting is because that is where we have always seemed to have the most problem,s starting.

Believe it?Does your bike start better?Don't look a gift horse in the mouth :)
 

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I'll atest to it. Changing the position of them made a world of difference for me. I'll admit I don't totally understand why it works, denny did put it pretty clear. All I know is it does.

Yes, this is a mod to alter the finely tuned jap machine that is set to optimal performance from factory.
 

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actually moving the pickup coils does in fact retard and advance he ignition... if you move the coils one way the rotor sends the signal a millisecond sooner (advancing the timing) and moving the coils the other way makes the coils sense the trigger later, thus retarding the ignition curve... I have messed with the pick up coils a lot... to find the optimal place to set them... Also, the Pickup coils do not spark...it is just a fancy magnet.

http://racetechelectric.com/ft-752-pulser-coil-ignition-systems.html

so your theory on making a hotter spark is incorrect. as Ron/Lance explained it to me, moving the pickup coils closer to the flywheel advances the timing a degree or so. no(w) go to basic automotive distributors for a minute... when the engine is off, the counter weights are at rest to advance the timing slightly to help in starting the engine, as soon as the engine starts turning at a given rpm, the weights then spread out to retard the timing back to normal to prevent pre-detonation.

Kawasaki set the pickup coils retarded to help pass emissions.
Slim, I think you have the explanation reversed as to how the weights on an automotive distributor function.
Ignition advance is least at idle and increases as engine speed increases. Think about it. As engine speed increases you need the spark sooner so the fuel mixture starts to burn sooner as it has less time in each cycle.

For example, my old GM pickup with a 350 V8 had initial advance at idle set at something like 10* BTDC with the vacuum line disconnected. As engine speed increases and centrifugal force spreads the distributor weights, advance increases to a maximum of perhaps 30* BTDC by 3000 rpm. The vacuum line is to help increase advance too, but I don`t remember exactly how it is set up.

When I installed propane carburation it could take more advance sooner, as propane has a higher resistance to preignition than pump gas does.
The propane specialist installed heavier weights so the advance curve was quicker, or shorter, so that maximum advance was reached at something just over 2000 rpm.
It has been a long time since I`ve had to set advance on a distributor, so my numbers may not be exactly correct, but you get the idea.
 

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I did the mod and I'm happy with it. As kanuck69 said, "it works", don't know just why, but it does for me so I don't really need to understand just why. I'm getting old and need to use what little brain cells I have for other things, like speling. :)
 

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Slim, I think you have the explanation reversed as to how the weights on an automotive distributor function.
Ignition advance is least at idle and increases as engine speed increases. Think about it. As engine speed increases you need the spark sooner so the fuel mixture starts to burn sooner as it has less time in each cycle.

For example, my old GM pickup with a 350 V8 had initial advance at idle set at something like 10* BTDC with the vacuum line disconnected. As engine speed increases and centrifugal force spreads the distributor weights, advance increases to a maximum of perhaps 30* BTDC by 3000 rpm. The vacuum line is to help increase advance too, but I don`t remember exactly how it is set up.

When I installed propane carburation it could take more advance sooner, as propane has a higher resistance to preignition than pump gas does.
The propane specialist installed heavier weights so the advance curve was quicker, or shorter, so that maximum advance was reached at something just over 2000 rpm.
It has been a long time since I`ve had to set advance on a distributor, so my numbers may not be exactly correct, but you get the idea.
Yes, timing is rpm dependent, but it's actually more complicated than that.

High engine vacuum occurs when the throttle blades are mostly closed. This allows very little charge to get into the cylinder... and there's not much air to compress. Very little cylinder pressure is built, and the charge burns slowly. These high vacuum conditions require a lot more ignition advance... regardless of rpm.

High load (throttle plates more open) allows a lot of air/fuel into the cylinder. This builds much more cylinder pressure, and burns much more quickly... requiring less advance... regardless of rpm.

The vacuum advance on a distributor adds timing at high vacuum. This increases efficiency and enhances fuel mileage. With modern electronic fuel injection, the computer takes info from all the sensors and takes care of it.

On a side note... Serious drag cars will often retard a few degrees of timing in high gear, as the engine has built a lot of heat, and doesn't need quite as much timing.
 

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so I too am not sure why decreasing the gap at the pickups is supposed to help
The shorter the distance that either an electrical spark OR a magnetic pulse has to travel, the greater the transmission of same (think "loose ground wire"). Same way that if you close the recommended gap on a spark plug a little, the spark is hotter (albeit may foul or burn out quicker). Think also, of two magnets drawn together. The closer together you get them, the stronger the pull, no ?
Close either TOO much, and the reaction negates itself. IE, no spark at all (closed circuit), or the magnets stick together.

...*shrug*...goin to bed....
 

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Discussion Starter #20
Appreciate all the input.
 
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