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honda bf100 no spark

M

molson1959

New member
Hi all,

I need help, i am at wits end with this honda.

I have read thru most if not all posts that refer to this problem, and have found many useful troubleshooting tips here, thanks all for the helpful info.

Here is the lowdown, the motor ran great for about an hour last week while out boating. Then when i went to restart it, i discovered i had no spark, or at least couldnt see one. I have read that it is difficult to see the spark at the best of times. Regardless, the motor would not start.

When i got home, i waited until after dark to check spark in the pitch black of my garage, No Spark.
This is when i found your web site/forum

I replaced the the ignition coil because the meter readings i took indicated that it was out of spec, unfortunetly the new one from Honda had same readings.

Here is what i have found/checked so far.

This motor has a CDI type ignition and is around the late 80's vintage.

ignition coil - spark plug lead to spark plug lead, 27k ohms, i have read on this forum in several places that it should be 8k ohms, the old one and new one are 27k ohms
ignition coil - primary to ground, 0.56 ohms
pulsar coil under cam, 130 ohm to grd
exciter coil under flywheel, brown wire to grd 340 ohms
stop switch not grounded, actually disconnected it from ground just to be sure.
neutral switch changes state when switching into neutral
i rang out all nine wires from CDI unit, all ok
checked and cleaned every connector
Just for fun, i did a compression check, both cylinders around 125psi, within 2psi of each other, as well as the ignition and valve timing- all good.

I am not a marine mechanic by any stretch, but do have mechanical/electronics background, so i know my way around a DVM.

I suspect the CDI unit is flaky, but i dont want to buy a new one, only to find out its not the problem.

Does anyone have any thoughts on this, I love this little honda because it is so simple and easy to work on, but now my frustration level is just about off the charts.

Any help would be greatly appreciated.

thanks in advance

mike
 
Hi Molson (the beer?):)

Anyway, yep Hondas putting us at wits end....I'm with ya bud!

It sounds to me like you know what you're doing and I ain't no guru with this stuff. But, I hang out here to learn things and offer a small cheering section for anyone with enough gumption to fix their own gear.

Been awhile since I worked on one of these old beauties but I still love them dearly.

Smart move checking for spark in the dark.

I don't know but this could simply be a case of a shorted or maybe even open spark plug. This system is "gang fired"....meaning both plugs fire together regardless of cylinder stroke....also known as a waste spark system.

The coil NEEDS a parallel path to ground to properly discharge through the high tension wires.
That's why you can't check spark with both plug caps off.

By the same token, I'm sure you understand that a plug shorted to ground will also kill spark.

So, we have to start with plugs

As far as specifications go, I have notes in my shop manual where I took some readings from a running engine. I have crossed out the 8k ohms for secondary resistance and wrote in 31.5 k ohms. I think it was probably a very hot SoCal day.
Anywho, it indicates that your 27k ohms reading for those coils is "in range".

The primary winding resistance is listed as 0.58 ohms but that day I measured 0.8 Ohms....and I think both are close enough.

The exciter coil resistance is listed at 330 ohms and I have no argument with that.

The pulser coil is listed at 120 ohms and I have measured the same or close to that.

I was surprised to read that you bought a new coil. I thought most things for these old gals had become unobtanium.

Well sir, that's all I have. I hope you can get things sorted out.

Oh! One more thing....
You might want to check the cranking volts at coil primary. I don't know what it's supposed to be. I have always kicked myself for not checking that and writing it down when I had the chance.

Good luck and please let us know what you find.
 
jgmo said:
Hi Molson (the beer?):)

Anyway, yep Hondas putting us at wits end....I'm with ya bud!

It sounds to me like you know what you're doing and I ain't no guru with this stuff. But, I hang out here to learn things and offer a small cheering section for anyone with enough gumption to fix their own gear.

Been awhile since I worked on one of these old beauties but I still love them dearly.

Smart move checking for spark in the dark.

I don't know but this could simply be a case of a shorted or maybe even open spark plug. This system is "gang fired"....meaning both plugs fire together regardless of cylinder stroke....also known as a waste spark system.

The coil NEEDS a parallel path to ground to properly discharge through the high tension wires.
That's why you can't check spark with both plug caps off.

By the same token, I'm sure you understand that a plug shorted to ground will also kill spark.

So, we have to start with plugs

As far as specifications go, I have notes in my shop manual where I took some readings from a running engine. I have crossed out the 8k ohms for secondary resistance and wrote in 31.5 k ohms. I think it was probably a very hot SoCal day.
Anywho, it indicates that your 27k ohms reading for those coils is "in range".

The primary winding resistance is listed as 0.58 ohms but that day I measured 0.8 Ohms....and I think both are close enough.

The exciter coil resistance is listed at 330 ohms and I have no argument with that.

The pulser coil is listed at 120 ohms and I have measured the same or close to that.

I was surprised to read that you bought a new coil. I thought most things for these old gals had become unobtanium.

Well sir, that's all I have. I hope you can get things sorted out.

Oh! One more thing....
You might want to check the cranking volts at coil primary. I don't know what it's supposed to be. I have always kicked myself for not checking that and writing it down when I had the chance.

Good luck and please let us know what you find.
Click to expand...
thanks for the reply,
i forgot to mention that i changed out spark plugs as well.
i didnt know you had to have a parallel path for both spark plugs. i assume i can just grd both plugs while trying a spark check then?
i did get one spark while checking again last night, but only one.
i would sure like to know what i am supposed to be seeing as far as voltage at the coil primary while cranking the motor over, anyone know what i should be looking for, roughly.
thanks agian

mike
 
Check your trigger coil voltage output, should be around 4-5 volts at pull start speed. Then check charge coil output, should be around 90 volts. If they are good then your cdi is no good. BTW these voltages are with a DVA so dc.I'm not a fan of resistance tests on cdi systems
 
Hi iang,
I checked the voltage to the ignition coil primary wire, getting about 0.4 - 0.5 vdc while pull cranking motor, i did this check with ignition coil wire disconnected from coil.


I also checked the trigger coil voltage while cranking, only getting about 0.1 - 0.2 volts dc, i did this check with trigger coil wires connected to CDI, not sure if this is what you had in mind, i dont know if the CDI unit would be pulling down the voltage



thanks
mike
 
Hi all,

Just thought i would report back on my no spark status.

Problem solved, it turns out that the nuetral switch is flaky.
I shorted the switch and the engine started second pull.
Gots lots of spark,
All good now.

When i tested the switch with my meter, i saw a change of state when switching from neutral to forward and vice versa, so i assumed the switch was fine.

I hope this may help someone in the future.


cheers
mike
 
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