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BF8A no spark

D

Diarmaid

New member
Hi guys,

Bought a used non-runner for cheap, with no spark.

So I've tested the kill switches, neutral switch, etc.
I've tested resistances on the CDI and they were way off, so thought that was the issue. Saw a video only of a guy heating up a CDI in the oven to fix it, tried that and the resistances came pretty much back into line.

So after bolting the CDI back on, I cranked the engine using a drill to check for spark. Still no spark... Until I messed with the kill switch.
I noticed that while cranking, every time I turn the kill switch on and off again I get a spark.
The spark is only when I mess with the switch, and not in necessarily in time with the engine.

Any thoughts?

Does it sound like a trigger coil, or cdi is at fault?
Should I bake some of the other components? Resistances on the other components are in range of the specs.
 
chawk_man said:
On most outboards, simply disconnecting the wires to the kill switch take it out of the loop.
Click to expand...

The kill switch is tested and working fine, I've taken it out of the loop also.

The strange thing is that when I turn off an on the kill switch while cranking the motor with a drill, I can get a spark in time with the frequency of the kill switch.
 
I confess I don't know a darn thing about the BF8A. But If I saw this on a typical small engine, my first thought would be that the stator is improperly grounded or totally shot.

Hopefully Mike or Jimmy, who know this engines very well, will chime in on this issue.
 
Resistance seems fine on the excitor coil, I'm going to give it a bake to see if it works better, as baking worked somewhat on the CDI.
 
I think what may be happening when you toggle the kill switch and get a spark is that the ignition coil is getting voltage and "charging up" as it's supposed to. Then, when you flip the switch it dumps the charge in the primary portion and that induces a large "spike" in the secondary portion causing a spark. That's how an ignition coil works and it seems you've discovered a new way to test a coil. The good news is that the coil is ok.

The CDI, along with the pulsar coil, basically does what you are doing with the kill switch. It allows volts to charge the coil and then breaks that connection to induce a large voltage spike in the coil that jumps the plug gap. Only it does it VERY rapidly and in time with the pistons being in the right place.

It knows the pistons are properly positioned because of the PULSAR COIL. The pulsar coil is located under a cover that sits on top of the camshaft sprocket. Sometimes, moisture gets in that small compartment and can corrode the connections or the coil itself. Take the cover off and check/clean the connections and make sure that the screws that hold the pulsar down haven't come loose. The coil can move and throw ignition timing off. Unplug the coil and check that it has 120 Ohms resistance. Plug it back in and see if there's any improvement.

Let us know what happens.
 
Last edited:
jgmo said:
I think what may be happening when you toggle the kill switch and get a spark is that the ignition coil is getting voltage and "charging up" as it's supposed to. Then, when you flip the switch it dumps the charge in the primary portion and that induces a large "spike" in the secondary portion causing a spark. That's how an ignition coil works and it seems you've discovered a new way to test a coil. The good news is that the coil is ok.

The CDI, along with the pulsar coil, basically does what you are doing with the kill switch. It allows volts to charge the coil and then breaks that connection to induce a large voltage spike in the coil that jumps the plug gap. Only it does it VERY rapidly and in time with the pistons being in the right place.

It knows the pistons are properly positioned because of the PULSAR COIL. The pulsar coil is located under a cover that sits on top of the camshaft sprocket. Sometimes, moisture gets in that small compartment and can corrode the connections or the coil itself. Take the cover off and check/clean the connections and make sure that the screws that hold the pulsar down haven't come loose. The coil can move and throw ignition timing off. Unplug the coil and check that it has 120 Ohms resistance. Plug it back in and see if there's any improvement.

Let us know what happens.
Click to expand...


Yeah....

So I baked my CDI again without success. Then I tried chipping out the resin in the case to get to the electronics, very difficult to do. I've already cracked the PCB in one area!!

Does anyone know where I can get a cheap CDI?

Is it possible to use a generic CDI from EBAY without paying the big bucks for Honda parts?
 
jgmo said:
I think what may be happening when you toggle the kill switch and get a spark is that the ignition coil is getting voltage and "charging up" as it's supposed to. Then, when you flip the switch it dumps the charge in the primary portion and that induces a large "spike" in the secondary portion causing a spark. That's how an ignition coil works and it seems you've discovered a new way to test a coil. The good news is that the coil is ok.

The CDI, along with the pulsar coil, basically does what you are doing with the kill switch. It allows volts to charge the coil and then breaks that connection to induce a large voltage spike in the coil that jumps the plug gap. Only it does it VERY rapidly and in time with the pistons being in the right place.

It knows the pistons are properly positioned because of the PULSAR COIL. The pulsar coil is located under a cover that sits on top of the camshaft sprocket. Sometimes, moisture gets in that small compartment and can corrode the connections or the coil itself. Take the cover off and check/clean the connections and make sure that the screws that hold the pulsar down haven't come loose. The coil can move and throw ignition timing off. Unplug the coil and check that it has 120 Ohms resistance. Plug it back in and see if there's any improvement.

Let us know what happens.
Click to expand...


I baked the CDI again, but without success with regards to resistance values, so i decided to strip the CDI down, and maybe change the components on the board. This did not go well.

The PCB is encased in a brittle hard plastic, almost like Bakelite, this made it very difficult to get down to the board... (A vice, hammer, pliers, acetone, and dremmel where all involved)

During this process I damaged the board and then gave up on completion of the removal.

I decided to just buy a cheap "universal" 6 pin CDI from ebay and see if I can get it to work with the engine. (Around 15 EURO/ 15 Dollars including shipping.)

If this doesn't work I may buy from Impex Japan, - a place where you can get cheap original parts. - I really don't feel like paying 150 bucks for a second hand part that may not work, or 450 bucks for a new original part. (The Honda distributor network in Ireland is taking the piss, - list for the part is around 320 but they are quoting me around 450... )

I will update when I receive the cheap CDI.
 
I received the cheap CDI yesterday, and after some tinkering with a soldering iron, I was able to get the engine to fire up!!!!!!

I only had it running for a few seconds as there is no fuel line connected. (Sprayed some gas into the carb by hand)

I didn't to run it for long, and there are wires all over the place, so I have no idea if it will run right yet, I need to complete the build and do more tests etc.

I will hopefully get working on it again in the coming days, and I will update you on my progress.
 
I got working on the engine again last night for an hour, after connecting a make-shift fuel line.
The engine was starting fine but wouldn't rev without bogging and cutting out, so I cleaned out the carb with a wire from a wire brush (for the small passages) and some carb cleaner.

Now the engine runs perfect!

I just need to tidy the wires and make a bracket for the new CDI. :)

Not bad for 10 bucks!!! :) :) :)
 
Wow! That is a GREAT FIX! Very resourceful! I hope you will share specifics about the CDI unit you used and how you went about wiring it in so others here sitting on the old B 100 and 75's that won't run because Honda doesn't sell the CDI anymore can use them again instead of scrapping them.

THANKS for a GREAT SUCCESS story!
 
jgmo said:
Wow! That is a GREAT FIX! Very resourceful! I hope you will share specifics about the CDI unit you used and how you went about wiring it in so others here sitting on the old B 100 and 75's that won't run because Honda doesn't sell the CDI anymore can use them again instead of scrapping them.

THANKS for a GREAT SUCCESS story!
Click to expand...



So I bought a "universal 6 pin AC CDI" that "fits most chinese ATVS up to 250cc".

It looks like the same unit in the wiring diagram link below:
https://tinyurl.com/lamz5c7

The CDI will need to be AC powered for the old BF8A and similar. (Do not buy the DC type)

To wire it, just take a look at the linked image.
https://tinyurl.com/lamz5c7

The kill switch is activated when connected to ground.
AC ignition power is connected to the exciter coil.
Everything else is self explanatory (2 ground pins and ignition coil), apart from the trigger coil. - The BF8A trigger coil has two output wires, so you will need to connect one of them to ground, and the other to the CDI as labelled.
 
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