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Discussion Starter #1 (Edited)
Anyone familiar with the ignition system on 1985 Honda Fourtrax, 125cc? Scouring the internet and the darkest places on the web, and have not been able to find much. The quad was acquired recently as a project for my kids and I. We have made some progress but stumbling a little with the ignition system. Someone in the past has had issues and tried to bypass the CDI module. We have a schematic and trying to put things back the way originally intended but there is something different with the pulse generator shown in the schematic vs existing. The unit we have has some kind of cam system, that opens and closes a contact, like you would see on older machine with points. Its located on the upper left of the engine behind a plate marked 125 CDI. There is a green and red wire. The green wire leads to some kind of resister/capacitor mounted to the engine/frame near by. It does measure a resistance. The previous owner spliced the red wire and ran it to one side of the ignition coil, and doesn't seem factory. I've tried to locate in the harness where the red wire may have tied into previously but have not had any luck. Below is the schematic we have been working with. The schematic doesn't show anything in regards to a red wire or the resistor. I'm unsure if the red wire is supposed to go to the ground side of the ignition coil or if should go to the CDI directly as shown below. Any input would be appreciated.
1985 Schematic.png
 

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Welcome to the forum

The old machines can be a real mess to work with as engines get swapped from one year to another and wiring harnesses get Frankenstein-ed

The wiring diagram is of no use unless you KNOW what you are working with.

Please provide the VIN from the frame, the serial number from the engine and a pic of what is behind the CDI cover
 

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Discussion Starter #3
Welcome to the forum

The old machines can be a real mess to work with as engines get swapped from one year to another and wiring harnesses get Frankenstein-ed

The wiring diagram is of no use unless you KNOW what you are working with.

Please provide the VIN from the frame, the serial number from the engine and a pic of what is behind the CDI cover
Thanks for your response, I need to look a little harder for VIN and S/N. Here are a couple pics of the area of concern. Also note that I did find a tag listing it is a 1986 model rather than 1985. The limit switch shown in the first picture is NC, and opens momentarily when the cam comes around. My instinct tells me that the red wire is cobbled and should go to the CDI module, and green wire should go to the other side of the limit switch. Currently is wrapped around tied to a stripped area of the red wire.
 

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Yep - you have a real cobbled up mess there - the rotor is a magnet used to trigger a pulse generator coil and a set of points for a breaker point ignition.

Here's what you need to do: First, get the VIN from the frame and serial number from the engine to assure you have compatible units. Let's find out what you have to work with to aid in making decisions then make a decision whether pursue completing the project or absorb the loss and scrap the project.

You can attempt to restore it to CDI ignition or consider reverting it to point type ignition. Reverting it may be easier than restoring it as the parts for the CDI ignition are all discontinued and will require scouring scrap yards to assemble the necessary parts to repair the system. Reverting it may be slightly easier, but parts are even harder to find and it possible you will need to change the camshaft, coil, wiring, ignition housing and cover to revert to points, but that hinges on whether the engine was designed for CDI or points. My guess some Baptist Engineer (I can't use the word to describe a mechanic with a sunburned neck because the cancel culture administration of this website censors the word red nik) tried to convert a CDI designed ignition system to points and lacked basic knowledge of either system.

BTW - 86 parts are harder to find than 85 parts and the two systems are completely different - parts from one system cannot be interchanged with the other system, but with perseverance, the system may be made functional again.
 

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Discussion Starter #5
Yep - you have a real cobbled up mess there - the rotor is a magnet used to trigger a pulse generator coil and a set of points for a breaker point ignition.

Here's what you need to do: First, get the VIN from the frame and serial number from the engine to assure you have compatible units. Let's find out what you have to work with to aid in making decisions then make a decision whether pursue completing the project or absorb the loss and scrap the project.

You can attempt to restore it to CDI ignition or consider reverting it to point type ignition. Reverting it may be easier than restoring it as the parts for the CDI ignition are all discontinued and will require scouring scrap yards to assemble the necessary parts to repair the system. Reverting it may be slightly easier, but parts are even harder to find and it possible you will need to change the camshaft, coil, wiring, ignition housing and cover to revert to points, but that hinges on whether the engine was designed for CDI or points. My guess some Baptist Engineer (I can't use the word to describe a mechanic with a sunburned neck because the cancel culture administration of this website censors the word red nik) tried to convert a CDI designed ignition system to points and lacked basic knowledge of either system.

BTW - 86 parts are harder to find than 85 parts and the two systems are completely different - parts from one system cannot be interchanged with the other system, but with perseverance, the system may be made functional again.
Am i understanding correctly that a breaker point ignition does not require a CDI but does require a battery? What your saying makes sense with some of the wiring I've found. Originally I would guess the CDI system had a pulser rather than the point ignition.
 

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CDI is Capacitive Discharge Ignition - a capacitor is charged either by DC from a battery (DC CDI) or by an alternator coil (AC CDI) - the energy is stored in the CDI unit - when the pulse coil generates a spike of voltage (typically 3-5 volts), it triggers the CDI unit to discharge the capacitor through the coil - an approximate 100v spike is discharged through the coil generating an intense microsecond appx. 40,000 volt pulse of voltage resulting in a spark jumping the gap of the electrodes of the spark plug.

In a breaker point ignition, either a DC voltage from a battery is passed through the coil when the points are closed and the current its interrupted when the points open. When the flow of current through the is stopped, the magnetic field around the coil collapses and generates a spark at the plug or if it's a AC magneto system, the energy is generated by the flywheel and the points close momentarily to allow the energy of the magneto coil to discharge through the coil and create the spark.

So which type of ignition do you want for your project - determine that and then start collecting the required parts to assemble the finished product.
 

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Discussion Starter #7
CDI is Capacitive Discharge Ignition - a capacitor is charged either by DC from a battery (DC CDI) or by an alternator coil (AC CDI) - the energy is stored in the CDI unit - when the pulse coil generates a spike of voltage (typically 3-5 volts), it triggers the CDI unit to discharge the capacitor through the coil - an approximate 100v spike is discharged through the coil generating an intense microsecond appx. 40,000 volt pulse of voltage resulting in a spark jumping the gap of the electrodes of the spark plug.

In a breaker point ignition, either a DC voltage from a battery is passed through the coil when the points are closed and the current its interrupted when the points open. When the flow of current through the is stopped, the magnetic field around the coil collapses and generates a spark at the plug or if it's a AC magneto system, the energy is generated by the flywheel and the points close momentarily to allow the energy of the magneto coil to discharge through the coil and create the spark.

So which type of ignition do you want for your project - determine that and then start collecting the required parts to assemble the finished product.
Thanks for the info, we where able to get our machine running with the breaker point system. It was a big help just understanding that it was not factory. I think eventually we will look to convert back to a CDI, but for now we are going to keep working through some of the other issues. We had it out over the weekend and ran it a while. Runs pretty well and starts easily. It definitely rattles your teeth over the bumps, but the kids love it. One thing that has become obvious is an excessive amount of smoke as you throttle into it. It seems to be grayish/white. When idling smoke seems to go away. We put an aftermarket carb on it and cleaned the air filter, but no change. I checked compression and getting about 120psi. I'm more familiar with 2-Stroke engines and not sure if this is with-in an acceptable range. Is my best be a new piston and rings? Any chance someone has a service manual they could share for a 1986 125M?
 
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