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Honda B75 Weak Spark

No boats on fire....but several Fire Boats.....

Here is what I found on a B75K1.

Performed the measurements with a Stevens CD77 Analog Peak Voltage/DVA meter.

Voltage at spark coil measured at post with points and primer coil attached (everything attached to run the motor) Measured at the input post on the spark coil.....approx 125v

Voltage output of primer coil with points attached but not connected to the spark coil....approx 300v

Here is a good one.....when I measure the output of the primer coil only.......approx 15v- 20 v depending on how hard I pull.

Let the theories on that one begin!

I connected the negative lead to the grounding point of the spark coil for all the measurements. I also did the measurements with the negative lead connected to another screw on the engine block with the same results.

Mike
 
Wow, PAGE 3!

YES! That voltage difference IS significant and baffling. Can't wait to hear Berniek's take on that one.
Did you have the condenser connected to the points at all times?

I do know that the coil gets "pumped up" with voltage in increments as the stator magnets come around in two revolutions of the crankshaft. On the CDI units it's a function of charging the capacitor and the coil with the cap in SERIES with the coil and releasing it's energy INTO the coil when discharging. In the points diagram Seakaye 12 provided on the first page of this thread, the cap is in PARALLEL with the coil and seems to only provide EMF buffering when the points close.....???? or am I all wet here?

At any rate, that coil producing 300 volts means it does some serious work. Good to finally know the FACTS.
Thanks for doing that and sharing the results Mike!
 
hahaha....well.....I think we are now all very confused. I sure am!

OK Mike....I did exactly what you did....leaving things hooked up. All my previous readings were with everything disconnected.... Here's what happened:

>>>Voltage at spark coil measured at post with points and primer coil attached (everything attached to run the motor) Measured at the input post on the spark coil.....approx 125v
I get 190 VDC

>>>Voltage output of primer coil with points attached but not connected to the spark coil....approx 300v
I get 351 VDC

My readings are with my meter set to DC Volts....with my home-brew DVA circuit in place.

A couple of notes: On my digital meter...the readout jumps all over the place; the two readings above were the **highest** readings I observed. In no way were they **steady** readings......

And; as a reminder: My engine does not have a "Charging Coil" and rectifier installed. As far as I can tell...it never did have one. JGMO has already confirmed that those are optional (for battery charging I imagine...) but I thought I'd mention it here again. Does the lack of a charging coil affect these tests at all????

Hey Mike.....thank you so much for doing that. I'm sure that now that we have your numbers.....and all of us here ponder what they actually mean.....I will be a lot further along.

I pass the ball down the court.....
 
If you were using a drill to crank the engine, you probably had a little higher revolutions than I did....thus, higher voltage.

A charging coil is totally independent from the firing circuit.

It does sound like your measurements are consistent.

I am still thinking that the carburetor should be the next step. If that is the way you are going, be very careful taking it apart. There is no o ring set, float valve or base gasket available. An ultrasonic cleaner is the way to clean it, if you have access to one. The o rings will not be damaged by a water and cleaner solution.

Unfortunately, even the Honda Carburetor Manual does not say how to clean it. It is the only downdraft carburetor that Honda used on their outboards. Be gentle:rolleyes:

Mike
 
OK. I will look further into the carburetor. I have on a couple of occassions sprayed carb-cleaner down into the carb...and have sprayed it directly into the cylinders as well. Not a pop.

As for the propane test; I will try that first. What should I do? Just position the tip of a propane torch at the carb throat and open the valve just a tad to get a little hiss?
 
With a torch, you will need to gain access to the very inlet of the carb. I don't know how those outboards are configured as far as ducting and such but you don't want the gas having to do any "gyrations" to get into the venturi. YOU MAY NEED A HELPER. Because, you will probably need to play around with the throttle opening since, if you leave the plate in the idle position, the gas will "stack up" against it and will not enter the intake manifold. So, You can see that holding the propane bottle, spinning the engine AND manipulating the throttle could get complicated for one person.

You then simply open the valve pretty much as if you are going to want to solder and hold the tip right up against the carb throat or open intake duct. You can experiment with gas flow if you don't get immediate results but this fuel READILY mixes with the ambient air, enters most engines and fires pretty effortlessly if there is a properly timed spark.

It is safe. Safer than pretty much any other method. I will be using it tomorrow to troubleshoot a friends car. Works like a charm IF the problem is a fuel delivery problem.

GOOD LUCK!
 
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With the points in parallel its a magneto, not a CDI. In general if a magneto produces any spark at all its all working, the only possibility, if components test reasonably OK, for a weak spark is for points adjustment

The difference in the Voltages with/without the ignition coil is sort of expected, the ignition coil will be providing some loading.

I must say i just assumed when you were measuring, the points were connected. Since is when the current flow in this coil stops (by opening the points), the collapsing flux produces the sharp pulse. Without the points there is no current flow.
Technically, probably in practice the condenser in parallel with the coil (after the points are open) form a resonant circuit and the design is such it has a relatively long time constant. The charge side of the measuring circuit was one of the known unknowns (You got to love Donald Rumsfeld :)) The voltage may be even much higher and the limitations of the measuring equipment may mean you just can't measure the high pulse.

Well all is now good.

As an aside an article from Briggs & Stratton, dismisses a couple of old wives tales one of which:

A bright blue spark is best. A yellow/orange spark signifies weak ignition.
and their explanation:
Not true. Spark color determines virtually nothing. The hottest spark is ultraviolet which we can't see. Blue spark is cold in comparison to ultra-violet. Orange and yellow come from particles of sodium in the air ionizing in the high energy of the spark gap.

WHEN this engine is running we all expect virtual beers :)

Or from another forum
There is always six steps in solving a problem, or doing a project. The sixth step is always exactly the same and is decided before any other
step 1--Planning
step 2~5 yada yada yada,success or failure
step 6 - Drink Beer
 
>>WHEN this engine is running we all expect virtual beers :)

hehe....I'll let you in on a secret. ONE of you lives close enough to me that the beer might not just be virtual! I'm not gonna tell you which one it is just yet....I don't want to kill anyone's enthusiasm for helping me LOL!

Well; OK, Berniek...it's **NOT**you...over there in Australia. But for the others....I'll let you guess.

No test today; sorry. I'll try to get it done tomorrow.

PS: Yes; the points and condenser were installed and connected for all the voltage tests. Only for the early-on resistance tests did I have components completely removed from the engine.
 
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Sigh....

Well; first off...I cleaned and re-gapped the spark plugs to 0.020. Then...I set the points according to the "tone method" outlined above.

One thing that I noticed when setting the points:
The flywheel turns twice to each rotation of the camshaft.....and I noticed that the tone went away at **slightly** different points on the two rotations. That means what? That the points-cam is slightly worn? It wasn't off very much...but on one rotation the tone would go away when the mark F passed the reference...and on the next rotation it would go away a bit further past.....

Anyway....hooked up a propane torch....my engine has no air box or silencer or anything else hooked to the carburetor...so the tip of the torch fit right into the little "horn" at the top of the carb. It's a down-draft carb so I figured that was about as perfect a setup as there could be.

Cranked it over with the drill....and....nothing. Varied the throttle position from idle to wide-open.
 

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Perhaps it has something to do with different valve springs pushing on the camshaft on each rotation ?----Not a worn points cam.
 
Is it possible that the key slipped out as you put the cam on. The BF100 that I am working on drove me crazy slipping down.

Or....what racerone said.

Recheck the initial timing marks too to be sure the timing belt went back on correctly.

Mike
 
I think it might be time to find you a serviceable ignition coil. Anybody got any?? Or Ideas on where he could find one? Seakaye12 I think you did the "pane" test on the money and I'm convinced she needs a coil. That is of course after you answer Mike's question about the key.
 
In reviewing with fresh eyes your weak spark issue, all that I can say is from looking at the picture of the ignition coil, I see some rust at the two points of mounting contact with the engine block. This might affect the degree of spark the plug can deliver since everything is in reference to ground. I would remove the rust and smear some dielectric grease on it. It appears you have covered everything else in great detail, nice work.

On another note in this same thread, someone responded to a possible error in a Honda service manual publication in regards to the resistance on the ignition coil. I am here to concur with this published error. I have a new second edition 2012 Honda shop manual (6188224E2) that covers three models, BF 75, BF100 & BF 8A. It states to check the resistance between the spark plug wire leads at the rubber boots that travels back to the large black ignition coil, on the bench. I measured 28.4 K ohms on my 29 year old BF100 10 HP model. The Honda manual states it should be 8 k ohms, plus / minus 20%. I ordered a new one thinking it was bad. I measured the new one out of the box and it is 26.7 K ohms. I decided to keep my old one vs returning it, or trying to since it is an electrical item. The new ignition coil does appear to made better than the original. The new one is fully potted on the top side and also potted on the wire leads that terminate at the coil housing. This ignition coil is evidently a proven design as Honda has used it on several different models from 1985 all the way to 2006.
 
Hiya flo....

Thanks for the input. Yes; the coil mounts are rusty....but that was one of the first things I addressed....was to clean the surfaces of it that contact the block and the mounting screw. I wish it was that simple!

I guess I don't understand why a company like Honda would not want to support these older motors by seeing that parts are readi;y available. At least "maintenance parts" like carb kits.....and electrical parts that have seemed to be prone to failure. How big a deal could it be for them? Its not like they have motors dating back to the turn of the century; 70's and 80's motors are considered "recent" by so many fresh water boaters.

I found a coil for mine; supposedly "available" by an on-line supplier. However...I e-mailed them to confirm availability and was not even graced with the courtesy of a reply....
 
Hi there! I'd need some help over here in Europe :)

I also have a B75K1 with no spark at one plug and with weak spark at the other. Did you manage to make yours work at the end? I suspect I will have to change the flywheel, primary coil and ignition coil together...

Anybody has such parts for sale? :)

Thanks!
 
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