late 80's Honda BF9.9A dead coil (new and old)

Hello all,

I got a honda BF9.9A (late 1980's) with a sailboat I purchased. When it came time to hang the motor and get it in the water, the motor wouldn't start. Diagnosis showed the coil was dead (zero resistance, open circuit on the secondary coil). This is a 2-plug coil, so resistance is measured between the two sparkplug connectors. I even pulled plug wires off and tested at the coil. No continuity.

A new coil was ordered. It sat on the bench for a month while we used the sailboat with a different motor. I need to put the motor away for the winter, so I finally installed the new coil, the unit started fairly easily. Shut down and restarted a few times as I've got no water flow (spent a few minutes diagnosing that the telltale isn't plugged, time for a waterpump replacement). Head in to tell the wife the bad news, and when I come back out it won't start. No spark. Pull out the multimeter and sure enough there is open circuit on the secondary coil.

This new coil has run for 5 minutes and is dead. I anticipate the dealer not wanting to order any sort of warranty replacement. At $165Cdn before tax, I don't want to pay for another one without a clearer picture of what's going on!

I'm too new, so I can't attach the wiring diagram for the motor... but it's fairly simple...
-exciter coil to power the CDI
-separate charge coil to the charging circuit (independent from the CDI system)
-cam pulser coil to signal CDI to spark
-oil pressure switch & light
-stop switch

Coil can't really be installed backwards; two wires, one is input, one is ground, there are no diodes or circuitry in the coil.

Has anyone ever experienced a replacement coil failing that quickly?
Could the CDI unit somehow be frying the coil?

Suggestions?

Hi NorthernBeek,

That is definitely a strange circumstance. I've not seen that happen before. I have never seen an exciter coil put out too much voltage but, even if it did, it would probably fry the primary coil, not the secondary.
I agree that buying another coil before you gather more info might not be wise.


It sounds like you know what you're doing so not trying to insult you but just going back over the basics...

The coil secondary should be in the neighborhood of 30k ohm measured with the caps on. Are you using a quality dvom and is it set on the corresponding scale?

Did you check for continuity between primary and secondary? Should be infinite ohms. Infinite to case for both windings as well.

I haven't worked on one this old but I'm not aware of any coils for these that have removeable plug wires. You stated that you originally removed the plug wires to check the coil resistance without them. Did you also remove the wires on the replacement you bought? I don't know that they have the twist off retainers ....do they?

You never mentioned spark plugs. Have you looked at them? A VERY wide gap could stress the coil for sure.

These engines will start and run surprisingly well and fairly smooth on only one cylinder. If one plug was failed with high resistance you might not notice that until you applied a bit of load. Although, I still don't see that failing the coil in such a short time. You never know however.

This is a puzzle to me for sure and I hope you get it sorted out.

Just remember, coils can and do fail right out of the box and NEW has always stood for Never Ever Worked. Our replacement parts "stream" seems to have deteriorated in reliability in the last few years and the consumer doesn't have much choice but to pay up. Sad state of affairs for sure.

Best of luck.

PS...what boat are you sailing?

Hey jgmo,

Thank you for the well thought out reply!

As an update... the plug wires do come off the coil assembly (threaded caps). I tore apart the old one, determined one wire is bad, and that the factory spec of 8.01-9.79 ohms should be K ohms... my old coil appears "fine", it just had a bad plug wire. That led me to pull the wires off my new coil, and determine that when you're frustrated to make mistakes, and while I've got a decent meter, it's not auto-ranging.... so 2 plug wires (averaging about 10k ohms each) and a coil at 8.5k ohms puts me right around 30k ohms... when the meter is set to the right scale. *facepalm*

So... my original coil assembly was bad (since it doesn't appear you can replace a single wire from the parts diagrams, just the plug cap which I haven't tried disassembling yet). That let to a general assumption that I was seeing a dead new coil. Based on my reassessment, I believe the coil is working now.

Back to the motor.... exciter coil and pulser coil both pass the correct spec for resistance. Plugs are new and gap has been reset (I originally had it too wide... misread the spec or used a crappy borrowed gapping tool).... doesn't mean they are good... something else to inspect. Stop switch tests good. Ran out of time yesterday evening to do anything else.

When I've got time I'm going to go through everything again, then do the basic tests on the CDI for continuity.

Thanks again for bouncing ideas! The sailboat is a mid 70's Canadian Sailcraft CS22. Swing keel arrangement. It's been a fun first boat for the month we managed to use it.

Well, your CS 22 reminds me a bit of my Clark Boats San Juan 23. The 23 is a masthead, centerboard sloop and is heavier at 2700lbs. Which has me thinking....
That 9.9 Honda is a whole lot of outboard for a 2200lb sailboat!

Anyway, it sounds like you are on the right track looking at the ignition system but I will add that the spark on these can be very faint in daylight and can fool you into thinking there is none when checking visually and pulling over by hand. The exciter coil puts out minimum volts when pull starting.

That, coupled with the fact that the carburetor on an outboard that has been unused for a time can cause issues that could have you chasing your tail. For those reasons I recommend watching for spark in the dark or under a cover of some sort while pulling it over. That or hook up a timing light with a car battery.

If you detect any sign of spark then try using artificial enrichment (I use propane) to see if she'll pop for you.

Just so you know, better men than I have been unsuccessful using that CDI crosscheck ohm chart in the shop manual. I hope you have better results if you get off into doing that.

Good luck.

Good luck.

So it appears I'm chasing a CDI or wiring issue. It started multiple times today, then sputtered when wiggling the connectors on the CDI... after messing about with pins it won't start again.

I'm looking at getting a DVA so I can properly measure the various voltages in and out of the CDI. I haven't been able to find any information online...

Does anyone know the approximate minimum voltage values for the various components? Exciter, pulse, ignition coil...

Maybe I should skip spending $58 on the DVA and just buy the CDI.

Oh... and my CS22 is 2200lbs dry. Ran it around with a 25hp which felt like a whole lot of motor. The kicker plate was only rated upto 20hp I believe... I never bothered to open it up to see how fast we could get it moving. Figured I didn't want to mess up my kicker plate or drop the motor!

I have not measured voltages from the exciter or pulsar coils and I regret not doing that and putting them in my notes.

The exciter coil resistance shouuld be near 330 ohms +/- 10%.

The pulsar coil windings should measure about 120 ohms +/- 10%.

You probably already knew that. But, if the continuity is there for a mag coil, and it produces measurable voltage when excited I assume it would be good. Yes, I realize assuming isn't the best "test" method but it's all I have to offer at present.

It's definitely possible that the CDI is bad but I wouldn't order a new one before exhausting all effort to verify the wiring. The most effective method that I know of for doing that is to load test using a sealed beam headlamp and a 12 volt battery. Isolate and load each wire looking for the lamp to shine brightly and then start wiggling in different places to see if you can interrupt the current flow while observing the lamp for dimming.

Since the CDI fires the engine sometimes I would be more suspicious of corrosion in the plug end wiring connector crimps than the encapsulated CDI pins being loose.

One other thing that I wanted to ask you is if your outboard is equipped with the neutral safety switch mounted on the shifter linkage horizintal rod under the hood? If so, that thing is known to cause starting problems. It consists of a Y shaped plate that rotates with the rod to block and unblock a magnet that closes a "reed switch" in the ignition ground circuit. Probably not causing your issue but, if you have one, something to be aware of. They get loose and out of adjustment as well as the reed switch arm breaking and shorting internally. It is not kosher to bypass a safety device but it can easily be done for testing purposes.

Standing by, hoping you have some success.

Hi Guys
Here's a few images with some specs which should help your diagnosis

Thank you Tony!

Funny, I'm convinced the honda literature is wrong for the ignition coil secondary windings. All the of the values I've seen in literature are the same 8.01-9.79 ohms... not Kohms. Both coils I have measure in the 8.4 Kohms range on the secondary windings (Kohms also jives with so many other automotive applications for secondary coil windings)... and I've narrowed down my original coil had a bad plug cap on one wire. (In the meantime, that bad cap and some very widely gapped plugs seems to have caused damage to the CDI... but to be determined).

Any chance that manual you've got has the peak voltage readings? I didn't want to buy the manual only to discover it doesn't have those values. Looks like Honda switched to using peak voltage for diagnostics in the early 90's once CDI systems were more common and testing resistance on a CDI proved inaccurate. (Found an informative Honda diagnostic video from the early 90's where they explain how to test CDI systems on a couple of small engines)

Hi, totally agree that K is far more realistic, the 9.9A manual only has those resistance checks for the CDI, I’ll see if the later one has DVA figures which no doubt should be very similar to the A model.

Tony Outboard said:

Hi, totally agree that K is far more realistic, the 9.9A manual only has those resistance checks for the CDI, I’ll see if the later one has DVA figures which no doubt should be very similar to the A model.

Click to expand...

Nothing WRT DVA in the later manual I have either i'm afraid.

I got some good help here so I thought I would chime in as I had a similar problem..

I tested everything, never was able to get the same readings on the cdi as the book said. Had a spare and made a CDI swap, still no start, I checked and cleaned every connector, loosened, cleaned and tightened each ground still no start. Spent some hours. Turned out to be the choke.. yes indeed..

There is a positive stop for both open and closed positions. If the rod gets bent you could be trying to run with a partially closed choke or trying start without the choke closed as needed. Either condition will cause you problems. The idle mixture is a set number of turns (varies depending on carb) and really does not deviate from that and the starting procedure requires full choke and the throttle handle in the start position...If everything is correct the motor starts on the 2nd pull, maybe third. You can see and feel the choke stops ion the lever if you disconnect the rod from the butterfly. Its a real minor difference in how the choke rod is bent.. too long or too short and you will have problems.. I discovered it by disconnecting the choke linkage and operating the choke butterfly by hand. After bending the rod a couple times I got it correct.. Full choke was full choke, choke off was choke off and now it starts on the second pull. The throttle handle cable tension also needs to be correct for these things to start as they should. You need that slight opening of the throttle plate that you get with the handle in the start position..but not so much that engine races too high.. thats bad news on a cold engine with no load.

I resurrected a few of the old 10hp cdi, Sometimes I remove the pull started and use a power drill and a socket to spin them to get em started. I had one that sat for a while and never would have got it running pulling the rope. Just be alert and lift the drill off when she fires.. and keep your face out of the way,.

FWIW the honda manual is way more valuable tool than the dva meter if you want to keep the motor.. Get it direct from honda for just under $50, not the ebay stealers..

Good luck,.

So my DVA adapter arrived and I did some testing last week; I wasn't happy with the numbers so I waited a few days and did them again...

CDI output to the coil is very inconsistent: 0-8V, often 1v or less, once saw 25v. If I do get a spike in voltage, it's only once and then voltage tapers off to nothing for a while.
Pulser coil : 4.4-4.8v consistent
Exciter coil : 250v consistent

Load tested all wires as good.

Based on the inconsistent and near zero output from the CDI, it would seem to be the problem. When I checked the resistance values on the exciter and pulse coil they were within spec.

Far assessment?

Well, just my opinion but I think you've done enough testing to justify ordering a CDI.

Thank you for posting the numbers too!

Looking forward to seeing your FIX report.

Long awaited update post. A new CDI came in, sat all winter, and I finally popped it in this Spring. Motor fired up on the first pull. Runs beautifully. Fingers crossed it stays that way!

That's GREAT NEWS NB! Congratulations on your success! I love it when I hear about one of these tough, old (but still pretty quiet) twin Hondas being brought back to service.
Thank you for taking the time to update your post and report back.
I hope your boating summer is a sensational one!