Full Power Ignition Mod

[bikerphil]

I just did this mod to my 79F which has 82XJ 3Ω coils with no ballast resistor. Got an extra volt or so up at the coils, not sure if it makes any difference powerwise...we'll see.

http://www.wgcarbs.com//index2.php?option=com_content&task=view&id=12&pop=1&page=0&Itemid=26

[n0lan]

I've done this mod to my 79 CB750

made a huge improvemnet.

I was wondering if this could be done on a XS11 79 Special. 3Phase suggested it wouldnt be a good idea b/c of teh ballast resistor as well as other things.


Nolan

[randy]

A lotta Hooey.

The guy writes well, but if you're losing voltage between your battery and the coils, I would find and correct the poor connection instead of installing another point of failure.

[DGXSER]

Hmm...I think the difference as I see it is that Phil stated he had already switched to the 3 ohm XJ coils. the 81 XS also has the 3 ohm coils. This eliminates the ballast resistor as Phil stated he had done.

I belive that 3Phase was stating that without eliminating the ballast resistor and changing to the 3 ohm coils, it would be a bad idea to switch. If you made the mods Phil stated, I think 3Phase would agree the mod can be successful.

[n0lan]

Hmm...I think the difference as I see it is that Phil stated he had already switched to the 3 ohm XJ coils. the 81 XS also has the 3 ohm coils. This eliminates the ballast resistor as Phil stated he had done.

I belive that 3Phase was stating that without eliminating the ballast resistor and changing to the 3 ohm coils, it would be a bad idea to switch. If you made the mods Phil stated, I think 3Phase would agree the mod can be successful.

Exactly.

The guy writes well, but if you're losing voltage between your battery and the coils, I would find and correct the poor connection instead of installing another point of failure.

and about creating another failure point, you could look at it from another view and say, you're elminating potential failure point[s].



Nolan

[bikerphil]

I would find and correct the poor connection

I totally agree, if I was stripping the bike down. That harness ain't coming apart anytime soon (knock), so I went with the next best option.

[3Phase]

Exactly.

and about creating another failure point, you could look at it from another view and say, you're elminating potential failure point[s].

Hey now! Don't ask me to approve ignition mods on your bike! On this one I agree with Randy -- find the voltage drop and fix it.

When I did the horn mod on my bike the little 30A Bosch relay failed. The two 1-ton van horns I'd installed went off in the garage at four-o'clock in the morning. I sealed and wired in the trusty old GMC horn relay from the van and haven't had a problem since but it was more than a little annoying.


The biggest problem with the relay is that because it is hooked straight to the battery you would not be able to turn off the engine when (not if) the relay stuck on!

If you try to wire in a kill switch you may wind up with the same voltage drop problem you were trying to eliminate with the relay and if you don't use the OEM kill switch you won't remember where it is in an emergency when you really need it anyway.

Of lesser importance, the TCI is supposed to have a protection circuit that shuts off power when the engine isn't turning with the key on but I've never tested it. You would not hear the ignition suddenly turn on all by itself, running down the battery and leaving the bike completely unable to start when you try to leave.

Do not fool around with modifying the ignition circuit, just fix it or leave it alone, "Lest ye die!"


Regards,

Scott

[Larrym]

Point to Point: The Complete Path

Phil,

I'm all for addressing less than ideal paths for the electrons to travel through and do what they're s'posed to do.

I would tend to see this mod as ideal for any of the bikes which still used points (dual or single) to control the on/off switching needed to make the all important spark. In the diagram for the mod the points would be somewhere on the ground side of the coils. Usually a short path through the points themselves and then to ground. The mod would ensure that the max possible power were available at the positive side of the coils and that's a good thing. The usual method on these old bikes is to route the power from the battery, through the ignition switch, back to the fuse box, and then through the individual fuses. Lots of opportunity for losses in the switch and connection points along the way and let's not forget the length of wire running between these components/controls.

On the XS, the route for positive power to the coils has the added length to/from the TCI and the controls inside the TCI. Shorter wire routing and beefier wire from the power source to the coils would make the electrons happier.

I'm just looking at the other side of the electron's path after it goes through the coils: the on/off switched path to ground. On the XS's this means the wires running back to the TCI where it serves the same purpose as ignition points would: on/off connections to ground. At running speeds this process would happen too fast to be handled by a mechanical relay so it's done through power transistors. Just the transistorized version of mechanical/electrical ignition points.

The mod does ensure the positive side of the coils is getting the best possible voltage/current. The negative side is still OEM.

But hey....If it did result in better power delivery to the positive side of the coils then that's a step forward.

[cywelchjr]

Phil,

I'm all for addressing less than ideal paths for the electrons to travel through and do what they're s'posed to do.

I would tend to see this mod as ideal for any of the bikes which still used points (dual or single) to control the on/off switching needed to make the all important spark. In the diagram for the mod the points would be somewhere on the ground side of the coils. Usually a short path through the points themselves and then to ground. The mod would ensure that the max possible power were available at the positive side of the coils and that's a good thing. The usual method on these old bikes is to route the power from the battery, through the ignition switch, back to the fuse box, and then through the individual fuses. Lots of opportunity for losses in the switch and connection points along the way and let's not forget the length of wire running between these components/controls.

On the XS, the route for positive power to the coils has the added length to/from the TCI and the controls inside the TCI. Shorter wire routing and beefier wire from the power source to the coils would make the electrons happier.

I'm just looking at the other side of the electron's path after it goes through the coils: the on/off switched path to ground. On the XS's this means the wires running back to the TCI where it serves the same purpose as ignition points would: on/off connections to ground. At running speeds this process would happen too fast to be handled by a mechanical relay so it's done through power transistors. Just the transistorized version of mechanical/electrical ignition points.

The mod does ensure the positive side of the coils is getting the best possible voltage/current. The negative side is still OEM.

But hey....If it did result in better power delivery to the positive side of the coils then that's a step forward.

So your basically saying we need a power amp on the TCI side of the coils to make that switch hotter? Kind of like a linier amp on a CB? I think we would all be better off just getting hotter coils, then there should be no problem anyways.

[Geezer]

A lotta Hooey.

The guy writes well, but if you're losing voltage between your battery and the coils, I would find and correct the poor connection instead of installing another point of failure.

I'm with you on this one...

Geezer

[Larrym]

TCI Function duplication/substitution

So your basically saying we need a power amp on the TCI side of the coils to make that switch hotter? Kind of like a linier amp on a CB? I think we would all be better off just getting hotter coils, then there should be no problem anyways.

Not exactly...I'm just pointing out that only the positive side of the coils was addressed by the mod. The negative side is the switched portion and our Bikes do run the wires back to the TCI where those power transistors are in place. It's part of the circuit that the mod circuitry/diagram leaves unmentioned.

Any connection/problems in this "return to ground" path would affect the total power delivered to the coils.

Any after market "mod" to improve the switched side of the coils would have to duplicate what the TCI does but more efficiently. Could get complicated real fast as the yamaha engineers made that TCI to work with the OEM pick-ups and all the associated resistances/impedances/voltages.

Like I said before...if the bike had a set of points controlling the make/break to the coils then the mod would have been a slam dunk improvement. In the XS that Switching on the other side of the coils is a little more than a pair of contact points leading to ground with a capacitor wired in parallel.

[bikerphil]

Well, I'll let you guys know if any ill effects result. I was too cheapazz to buy a pigtail connector, but I did put a 10A in line fuse near the battery. I mounted the relay with it's bare spade terminals where the RLU used to be, under the gas tank . I would like to see if the bike runs better with the higher voltage though. Not really worried about the TCI, just maybe a little about a fire.

[clcorbin]

Not exactly...I'm just pointing out that only the positive side of the coils was addressed by the mod. The negative side is the switched portion and our Bikes do run the wires back to the TCI where those power transistors are in place. It's part of the circuit that the mod circuitry/diagram leaves unmentioned.

I'm still tempted to work up a small electronic ignition module for this bike. It would be able to do away with the mechanical advance (we know the engine RPM and can set the advance directly) and vacuum advance (A small pressure sensor tied to that port on the carb) as well as all of the stock ignition components. Given just how small microcontrollers are and how capable they are, it would be pretty trivial to use one to drive a couple of ignition rated IGBTs for switching duties. Heck, we could even monitor coil current and set "dwell" dynamically and directly. While I was at it, I would probably set up an optical trigger to feed the TDC signal to the module and really get rid of all the 30+ year old stock components.

Maybe this summer I'll decide it's time to fire off a new electronic project...

[Geezer]

. I was too cheapazz to buy a pigtail connector,

If you need a pigtail connector (or a repair harness as I call them) let me know. I make them up for pretty cheap if I have the connector and the correct wire colors.

Geezer

[bikerphil]

Just an update on this:

I've run this setup for over 1000 miles and I do notice an improvement. No more occasional hiccup after sitting at a long red light. Don't have to blip the throttle first anymore. Guess that extra volt at idle helps some.