Pick Up Coil Mod-- Theory?? - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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Old 04-04-2012, 08:03 AM Thread Starter
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Pick Up Coil Mod-- Theory??

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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TOC upgrade on ACCT
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rectifier relocated
splines lubed
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decals removed
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Pic up coil mod done
degoated
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Old 04-04-2012, 08:50 AM
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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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Old 04-04-2012, 09:45 AM
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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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Old 04-04-2012, 11:29 AM Thread Starter
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[QUOTE=Knifemaker;203465]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.

JM2001

" Loud Pipes Risk Rights "

2001 Vulcan 750
marbled
TOC upgrade on ACCT
Air/fuel mixture set to 2 1/2 out
rectifier relocated
splines lubed
iridiums
decals removed
upgraded mirrors
Pic up coil mod done
degoated
All LED lighting
Upgraded Mosfet rectifier
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Old 04-04-2012, 11:48 AM
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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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Old 04-04-2012, 11:52 AM Thread Starter
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Quote:
Originally Posted by slimvulcanrider View Post
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

JM2001

" Loud Pipes Risk Rights "

2001 Vulcan 750
marbled
TOC upgrade on ACCT
Air/fuel mixture set to 2 1/2 out
rectifier relocated
splines lubed
iridiums
decals removed
upgraded mirrors
Pic up coil mod done
degoated
All LED lighting
Upgraded Mosfet rectifier
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Old 04-04-2012, 12:01 PM
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[QUOTE=JM2001;203487]
Quote:
Originally Posted by Knifemaker View Post
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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Old 04-04-2012, 12:49 PM
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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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Old 04-04-2012, 01:17 PM
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Quote:
Originally Posted by Knifemaker View Post
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>

Last edited by ZCraggRatt; 04-04-2012 at 04:41 PM. Reason: spailin'
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Old 04-04-2012, 02:47 PM
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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.

Quote:
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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