1988 Force 125 lost a cylinder

[roscottjr]

We were haveing a great time at the lake this weekend and suddenly lost a little power in the engine. It was acting like a fuel issue but after verifying the carbs were clean and getting fuel I decided to check on the elctrical components. I originally thought it may be the coil but later after a little testing and switching things around to confirm I found out that 1 side of my cdi pack had gone bad. At first the engine was jumpy like bad fuel then it got to where every few seconds it felt like an extra kick in the power so to speak. turns out this cdi was going bad and finally went. Anyway, is this just simply because the pack was old and lived its life or could something have caused this? These packs are pretty expensive so if something caused it then I want to get it taken care of as well.

Robert

 

[jerbear56]

Re: 1988 Force 125 lost a cylinder

The number one killer of power packs is starting the motor with low voltage.
That's the reason you see deep cycle batteries (marine batteries) recommended. Unlike car batteries, that can go from somewhat discharged to seriously discharged without notice, they have a steady discharge rate and are less likely to damage the module.

 

[roscottjr]

Re: 1988 Force 125 lost a cylinder

Ok, from my understanding this engine can run without a battery so why would a low battery cause the cdi pack to go bad?

By what you have said, I think it may be my fault the cdi went bad. The battery would just barely begine to spin the engine then stop because it was low, so i charged the battery. This was Thursday night. Got to the lake Friday and went for a quick 5 minute spin and all was fine. Saturday we played around, and also just rode around for a total of about 3 or 4 hours. Sunday it started acting up. The battery held full charge the entire weekend and still has a full charge. Is it possible the low battery damaged the cdi pack Thursday night and it just took that long for it to finally quit on that cylinder?

Robert

 

[pnwboat]

Re: 1988 Force 125 lost a cylinder

On the Force Prestolite ignition system, the battery has nothing to do with the CD Modules. You can pull start the motor with a rope without the battery connected and it will run just fine. The only purpose the battery has is to operate the starter and accessories. CD modules get their voltage from the stator. Voltage is created by the magnetic field from the magnets in the flywheel reacting with the windings in the stator. Kind of like a magneto.

It's not uncommon for the CD Module to go bad. Before you change it out, you should check the resistance of the stator, trigger, coils. Also the ground connections and terminal connections. Like you said, the CD modules are not cheap. Here is a chart that shows the resistance readings and voltages.

http://www.cdielectronics.com/LinkClick.aspx?fileticket=Jb6eaecTaO0%3d&tabid=55&mid=383&language=en-US

You can enlarge the chart for easier viewing.

 

[john from md]

Re: 1988 Force 125 lost a cylinder

Jerbear56, I must disagree with you regarding the number one CDI killer.

The number one practice that will ruin any kind of CDI module is cranking or running the engine with the plug wire removed and not grounded. On CDI type ignition systems, the energy that is not fed to ground, due to the the wire being removed, is fed back through the unit. Every time this is done, the components get weaker until they finally fail. That is why the best way to check spark on a CDI type system is with a spark gap checker.

I don't mean to say that you can't pull a plug wire off once in a while to check the cylinder, I am saying not to make it a common practice or it will cost you.

John

 

[roscottjr]

Re: 1988 Force 125 lost a cylinder

I always attach the plug wires to a spark tester if I am cranking the engine with a wire loose in order to use every spark. With that in mind, I think what I have here is simply a CDI that was possibly nearing its life cycle meaning there is more than likely not another issue that caused this. Am I correct?

Robert

Jerbear56, I must disagree with you regarding the number one CDI killer.

The number one practice that will ruin any kind of CDI module is cranking or running the engine with the plug wire removed and not grounded. On CDI type ignition systems, the energy that is not fed to ground, due to the the wire being removed, is fed back through the unit. Every time this is done, the components get weaker until they finally fail. That is why the best way to check spark on a CDI type system is with a spark gap checker.

I don't mean to say that you can't pull a plug wire off once in a while to check the cylinder, I am saying not to make it a common practice or it will cost you.

John

 

[roscottjr]

Re: 1988 Force 125 lost a cylinder

Also, does anyone know what other Force models have CDI packs that will interchange with this one? I found some for a 1988 125hp but he says its for "b" models and mine is a "c" model. I also checked and the part numbers do not match so Im pretty sure those will not work but Im not sure.

Robert

 

[john from md]

Re: 1988 Force 125 lost a cylinder

It could be that its time was up considering that these engines are getting long in the tooth.

Most 125hp CDI units will work between 1984 and 1989. There may be more but of those I am not sure of.

John

 

[jerbear56]

Re: 1988 Force 125 lost a cylinder

Jerbear56, I must disagree with you regarding the number one CDI killer.

The number one practice that will ruin any kind of CDI module is cranking or running the engine with the plug wire removed and not grounded. On CDI type ignition systems, the energy that is not fed to ground, due to the the wire being removed, is fed back through the unit. Every time this is done, the components get weaker until they finally fail. That is why the best way to check spark on a CDI type system is with a spark gap checker.

I don't mean to say that you can't pull a plug wire off once in a while to check the cylinder, I am saying not to make it a common practice or it will cost you.

John

I certainly don't have a problem with anyone disagreeing, but if you think about it, are you really disagreeing with me?

Just because I didn't go into detail doesn't mean we aren't on the same page. The flywheel is engineered to turn at a certain rpm, even when starting. When it's struggling to turn, it can and will place a voltage on the caps that is not high enough to jump the plug gap. In effect, it's like turning the motor over with the plug wire ungrounded and it causes the damage you described.

But I have to stand by my original statement. It's my belief that more motors are cranked on low voltage than there are running with a plug wire off. Usually those are pulled after someone has a problem.

And it's not uncommon for a component to get damaged and continue to do it's job until arcing and heat finally finish it off.

 

[roscottjr]

Re: 1988 Force 125 lost a cylinder

When the problem first started I was using a spark tester and noticed with the engine running that the number 1 cylinder was not firing normally. It would fire 2 or 3 times and then a few seconds of nothing and then a spark or two and another few seconds of nothing. I found it was the CDI after testing everything and shortly after I lost all fire on number 1 piston.

I certainly appreciate all the opinions and regardless of who believes what it looks to me that if I keep all of them in mind then I will be good. I cant say I believe 1 more than the other. I guess the question on CDI packs is almost like asking which brand is better. Everyone has a specific opinion and there may be 1 who is completely correct while another has a very good point.

I can definately say that all of you have eased my worries as to whether or not there may be another issue that caused the CDI to go bad. At this point I do not think there is anything else electrically that may have caused this. Thanks to everyone for your responses and I look forward to any more comments on the issue. I am eager to learn anything I don't know.

Robert