CDI vs Contact Points System. Pros/Cons Which is better (BF75/BF100)

So I have three motors that I am going try and get up and running. Hopefully all three but might have to use one for parts to make 2 working motors. Two motors are Contact Breaker systems and the other is a CDI system. Of the two contact systems ones a BF100 and the other is a BF75 (7.5). The CDI is a 7.5 also.

Is the CDI more desirable and why?

What are the pros and cons of both systems?


Thanks for the help in advance.

Jeff

I think most experienced techs would recommend the CDI ignition system over breaker point ignition. The CDI, being "solid state" tends to be much more reliable and fairly maintenance free as compared to breaker point ignition. CDI also provides for more precise coil primary "switching" that results in a fully saturated winding and hotter spark due to the longer "dwell" afforded by the nature of the system.

If most of the above is new or "Greek" to you, suffice it to say that, basically, you set up the CDI and forget it. With points, they are constantly wearing and arcing and need periodic adjustment and/or replacement. There is also a capacitor (often called a condensor) needed with points to keep arcing to a minimum and those tend to deteriorate and need frequent replacement as well. And, it's a small factor to be sure but a CDI system will create less electrical "noise". Something commonly called RFI or Radio Frequency Interference.
Not a huge concern on a small boat but may improve the quality of your AM radio reception if you're trolling and want to listen to the game.

Good luck putting your FrankenHonda together! ;~)

Thanks for the help.

Is there a thread out there that shows the prcedures for testing the BF7.5/100 electrical system? I want to run through all these motors and test all the electrical components. I have a basic mutil meter and a shop manual for the motors. Just need to know what setting to put the multi meter on so I am getting the correct results.

Is there a sequence to what you would start testing? Spark first? Then switches or other components that are typical causes or easy to get to next?

On the CDI motor I have in 7.5hp. I have a 10hp points motor. Would like to get the 10hp going for more hp. Can I swap the CDI from the 7.5 and drop it onto the 10hp? Or are there other issues that that will create and isn't worth the effort?

Thanks again for all the help of a newbie. I like to get deals and fix things up. Satisfaction of knowing how things work and easy way to get good equipment on a budget

Jeff

Never apologize for wanting to save a buck....learning how things work....or bringing back an old HONDA from the scrap yard. If it wasn't for guys JUST LIKE YOU, we wouldn't have all the venerable antique tools, cars, boats and planes to MARVEL at when we stumble across a gathering of them showing off what they've accomplished and having a fun time doing it. KEEP IT UP!

As far as testing the Honda ignition system, I don't have a lot on the subject. I have the Honda manual that has the basic resistance tests for the ignition coil ( the one with the spark plug wires) and the exciter coil ( the one UNDER the flywheel. One of the absolute best ways to "test" a given system is to pull the engine over in a DARK room while observing the electrode of a grounded spark plug. That is known as EMPIRICAL testing. IE: watching it ACTUALLY WORK. If you see a blueish tinted spark, it will likely fire the engine. These outboards do not produce the hot blue spark some people may associate with a car or even a lawnmower. It is fairly faint in broad daylight and is much easier to observe in the dark.

One thing I have noticed about "testing" is that the PUBLISHED resistance values don't match what I measure with my Fluke 87V multimeter. For example, the book says ignition coil primary winding should be 8 Ohm +or- 20%. What I've read is 31.5 consistently for BOTH CDI AND breaker point ignition systems. I SUSPECT that they mixed up the CDI EXCITER coil resistance with the IGNITION coil resistance...but...I'm not 100% sure YET. Maybe YOUR efforts to get your outboard built will reveal the TRUTH.

If you intend to use the CDI from one of the 7.5 hp on the 10, you may need to swap the exciter coil. The resistance for the points coil is listed at 2.0 Ohm and the CDI is listed at 33 IN MY BOOK. But you have three of them so you can do some testing and see what you find.

Other than the exciter coil difference between points and CDI , I think the only REAL mechanical difference between the 10 and 7.5 is the CAM shaft and the CARBURETOR. That's where they bumped up the HP rating another 2.5 HP. So mixing and matching parts...other than those two...should be fine. Except maybe......

.....For the CHARGE coil. You may find that one of the 7.5 outboards came with a slightly more powerful charging system than the 10. OR one of the 7.5 even HAS a charge coil and the 10 does NOT. Not likely but maybe. If so, you can take advantage of having the flywheel off to swap or ADD a CHARGE coil so you have the best charge system you can get. So don't forget to check that out.

Other than that, I say make sure the valve lash is properly adjusted, the timing is set...both cam and ignition...and give her a pull!

There is no doubt that in the modern world cdi is better for all the reasons stated By jgmo. I would just like to add however, there is nothing wrong a points based system, especially if you enjoy a bit of shade tree mechanics. Just remember that points are a service item and will require adjustment or replacement just like an impeller. In your situation I would do my best to get each motor going with its designed equipment first, before I tried replacing ignition systems. If you get it going then that's great and you have a working motor, if you want to try and put in a cdi and it doesn't work then you can fall back to your points and still take your boat out. I personally could not think of a better way to spend a few days in the shed tinkering (but I'm told that I'm weird!). Without looking at the specs but understanding that the likely only difference between the 7.5 and the 10 is the carby (this is very common for outboards of similar HP) then it may be easier to just swap the carby from the 10HP points motor to the 7.5HP CDI unit and you are done. Perhaps the cam in the 10HP is lumpier too and may need swapping. best to refer to the specs of each motor. Also check your specs for Valve clearance. Enjoy your tinkering and please keep us updated on your progress so we can all enjoy your shed time vicariously.

CDI is great for folks who do not know how to do their own repair work.-----Rush off to a dealer to get repair work done at $100 / hr.----------Old time points just need some " no money spent " maintenance work now and then.

So yesterday I dug into the motors. I started off by getting all 3 carbs and fuel pumps cleaned. All looked good. I then broke out the multimeter. Set it at 200 ohm.

Testing 2 points motors:
BF75Z- 1979
BF100- 1978

One CDI- BF75F- 1985 This motor started up and ran for a few seconds with a shot of starting fluid so I know I have spark on this motor.

I set the multi on 200 ohm setting. When I touched the red and black leads together I had .4 reading on the multi.

Primary Coil- On the 2 points motors I pulled the connectors apart and placed the multi leads to the two wires. The coils were still under the flywheel.
BF75Z= 2.6 BF100= 2.3 CDI BF75F= Cant test unless removed from motor according to manual

Charging Coil- Again pulled wires connectors and placed multi leads to the wires with flywheel still on.
BF75Z= .5 BF100=.5 CDI Charge Coil BF75F= .5

Next tested the ignition coil (Large Black Coil with spark plug wires attached)- Coil was still on the motor. I touched one multi lead to the mounting screw that holds the coil to the motor and the other lead to the threaded screw post on top of the coil.
BF75Z= 1.7 BF100=1.6 CDI BF75F= .9

So did I do my test correctly and what do the numbers work out to be? Picking up a spark tester today and seeing what else I can probe into as well as testing the kill switches and points/condenser. Just want to be sure I am on the right track and using the correct methods of testing.
Thanks,
Jeff

That all sounds like you did ok. What manual are you working with? If you can access wires to coils, I'm not sure why you would be directed to pull the flywheel.

One thing you DIDN'T check was SECONDARY resistance of the ignition coils. You do that by setting your meter on it's highest Ohm scale and putting the probes in the spark plug ends. You should get a reading of several thousand Ohms. This checks the internal resistance of the coil secondary and both spark plug wires all at once. All three coils should have similar but not necessarily the same excact resistances.

Meter set at 200 k the following numbers came up when I put one probe into each plug boot:

7.5hp= 35.9
10hp= 35
7.5hp w/ CDI= 29.6

Any of those numbers or the ones I already gave point to anything bad yet or is everything OK?

I don't see anything in your measurements that make me think you have any "bad" components. From what you've posted so far, it looks like you have yourself a pile of good parts. ;~)

And, the fact that you got some "pop" from the CDI engine is encouraging for sure.

You shouldn't need to pull the flywheel on any of these to adjust/replace points. All the ignition timing components are accessed under the cam pulley cover.

Thanks for the help again. Tried a spark test with the lights off in the garage last night and got no results. I used two different testers one inline that you leave the plug in and the other that goes into the wire boot, has an adustable metal screw and then clips onto a ground post on the motor. Again nothing.

Hopefully will have a compression check done in the next couple days and will order some new points. Looks like the only thing I havn't tested electrically is the points, condenser, and kill switch. Any tips for testing those? What setting and procedure?

Thanks,
Jeff

I do NOT recommend using a spark "tester" to check spark on the small Honda outboards. I usually just ground the threaded portion of first one plug and then the other and watch for spark in a dark space or even under a tarp. Here's why:

The coil under the flywheel that produces volts to power the ignition coil windings is RPM DEPENDENT. Meaning that the faster the flywheel spins, the more voltage the coil produces. Even with both plugs removed from the engine, you won't get much more than a few hundred rpm pulling the engine over with the recoil starter. Therefore, the coil produces a MINIMUM voltage for firing the ignition. It is a low energy spark that is produced and is VERY faint. Spark testers, along with how you sometimes need to hook them up, may provide mtoo much resistance for a good test.

Forgot to mention that when spark testing, it is ESSENTIAL that you VERIFY the ground you are using is a reliable one. Using your ohmmeter to do this is one way to verify ground.

Get back to us with the compression test results. Remember to have both plugs removed and the throttle held WIDE OPEN while cranking to get reliable results. It is probably more important that both cylinders on each engine test "even" than if they have "high" pressure readings.

On the 10HP I have good spark now.

I also finallygot my harbor freight compression tester and on the 10hp I have good spark andhave 110 on the lower cylinder and 115 on the upper.

I tested by removing both plugs and had the throttlewide open like jgmo suggested. In order to get the throttle wide open I had tohave the shift lever engaged in forward, would that change any readings? Itested each cylinder two different times removing the tester each timealternating cylinders. Each time I pulled the cord 4-5 times checked the gauge,reset the gauge and pulled 4-5 more times before switching cylinders.
On the topcylinder I hit 120 one time the rest of the time it was 110-115 and on thebottom cylinder I hit 115 once and the rest were 110.
Good test?Anything I can try to improve the compression before I get going into firing itup? Adjust the valves?

I think you're ok too. Putting the outboard in forward means you are not getting as much rpm on your pulls and I would expect the pressures would actually GO UP if you could perform the test in neutral.

Checking the valves for proper clearance is always a good idea and I would encourage you to do it.

So I was able to test everything on the 7.5 and 10hp points motors. Compression on both motors were in the 110-120 range pull starting. I got spark on all 4 plug wires. I have not adjusted any valves yet but droped both into a barrel and the 7.5 fires right up. I did put a new set of points in the 7.5 as I was not getting spark and did once I replaced the points. It idels great and can run RPM up and down without stalling out. Turn it off and starts back up on 1st pull as well as let it sit for a few hours and it starts right back up again. The motor was not used for several years and when I got it was laying flat on the guys garage floor with some oil leaking inside the case. I tried to clean it all up but couldnt get it all so when I first started it up I got some smoke from the exterior of the exhaust area as well as smoke from the exhaust output. Was worried at first but the smoke cleared up after letting it run a little. I think since it hadnt been run for a while it was just taking a little while to reseat or burn out all the gunk that was in there. Now it runs without much burnt oil small at all. I have only ran it for a bout 10-15 minutes total but all looks good.

On the 10hp I have good spark but cant get the motor to pop. I will check the valve clearance and then thinking about swaping the carb from the running motor to see if its a fuel issue now. If that doesnt work I will swap out the new points from the running motor to see if the points are the issue before I drop another $30 on a new set of hard to find points

Again thanks for all the help with this guys. I hope when I am all done I can post a thread condensing all the info, procedures, results I learned from this process.

Sounds like you're "ALL OVER IT" jduck1!
I bet you have that 10 purrin' pretty in no time!
Thanks for keeping us updated.