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Very weak spark 8 HP Yamaha

timguy

timguy

Silver Medal Contributor
I have an eight HP 2 stroke Yamaha. Very weak spark on both cylinders. Can barely jump 1/8" and pale color. It looks like extremely low hours and a mint condition motor. The coil is a single unit for both cylinders and a black wire as well as an orange wire. The motor will run, but I cannot trust it.
Has anyone experienced this before? I don't work on too many Yamahas, guess they just keep running good on their own.
It came to me for a water pump service. Compression is 110 on both cylinders. Please see photo for year identification. I think it's a 96 model with that "X"
Thanks, Tim
 

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Thanks, Racer. This is in like new condition, I guess 30 years took some toll on the electronics? Any ideas on repair?
 
Sorry I had a stop by 15 horsepower Evinrude repair.
Okay here's what we have.
What do you think of that?
Not enough resistance within that coil so it could be possibly shorting out inside? Remember this is a two-in-one coil.
 

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Ignition coil output to the spark plug is based on CDI output to the ignition coil.

CDI output to the ignition coil is based on the charge coil input to the CDI.

Test for charge coil output and CDI output.

 
Thanks. Tests completed. All within parameters while hand cranking, it's not electric start. Here is results.
 

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Weak spark on both cylinders usually points to a failing charge coil or CDI. Since both are affected and compression is good, I'd lean toward electrical, not mechanical.
 
Right, certainly. The DVA meter as well as ohms seems to show a properly functioning charge/Exciter coil, however. The capacitor module is always suspect, but in the case of a weak spark, I'm skeptical 🤔. I hoped someone with more experience on the Yamahas would say "oh I know exactly what that is I've worked on that one before". Once again CDI Electronics does not cover the two in one coil for this particular model and Yamaha forces us to spend more money on OEM. The part is expensive and I always wonder why people love Yamahas so much when they intentionally make parts expensive and/or hard to find. Yes I've run into this before with Yamahas in particular. There are cheap versions of that coil available but they are often ¢r@ppy and unpredictable in operation.... yes, I'm not enthusiastic about Yamaha and their tactics when looking for reliable replacement parts....options are limited.
 
utakts said:
Weak spark on both cylinders usually points to a failing charge coil or CDI. Since both are affected and compression is good, I'd lean toward electrical, not mechanical.
Click to expand...
That is why both are tested. Presumably tested by the OP and found to be within specifications.

If the CDI output to the coil is found to be good but the output from the ignition coil is found to be bad, one might suspect the coil as being the problem.
 
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Thanks Bosco. Have you had any history of problems with this coil in a low low hours motor? The testing procedure (specs by CDI Electronics), gives me 2.4 to 4.5 k ohms between cylinder 1 and 2 high tension leads. That's where I am getting 1.5 k. I have very weak spark but exactly the same on both cylinders. Does your specifications suggest the test between the input wire and the high tension lead? Also is the orange wire the input and the black wire the trigger? Or is the orange wire the timed input for cylinder 1 and the black wire the timed input for cylinder 2?
 
The ignition coil fires both plugs at the same time. Does not matter if the Orange wire is the input and the black is the ground or if the black is the input lead and the orange is the ground.

The test for the secondary coil is from one ignition lead to the other ignition lead.

It makes sense that if you are measuring a much lower resistance between the high tension leads that something is amiss within the coil. I might guess a connection of some sort between coil windings which could very well lower the output spark voltage.

Why are you not using the Yamaha service manual for guidance? I have no idea where CDI gets their data. Maybe from coils that are made by CDI but that does not necessarily apply to a Yamaha made coil.

 
Yes I don't use the Yamaha manual for diagnostics It's probably available online too, perhaps I should. But the CDI testing procedure is with original equipment suggestion and their own replacement parts parameters may vary slightly but not that much. That at least is what I found over time with working on many outboards that have been repaired with CDI components as well.
 
On a 4 stroke the both fire at the same time at TDC or nealy so.----I doubt they both fire at the same time on a 2 stroke.
 
Yup, holy cr@p that's 183 times a second at 5500 rpm. That's a he!! Of a task for that capacitor, brother
 
Formula 1 engines in the past revved to 18000 RPM or so.----Valves would open and close 150 times / second.----So making spark is easy.
 
When I put a regular Yamaha coil to the orange wire coming off the capacitor module I'm getting a tremendous spark. And nothing off the black wire. And yes it fires twice per revolution. So it's probably this foolish two in one coil. What do you think? Should I try one of those China cheapos?
 
It does fire off the orange wire with the black wire ungrounded but it won't fire off the black wire with the orange wire ungrounded, go figure?
Maybe that two fires per revolution causes a shortened life for that two in one coil? 🤔
 
Yes but how many pulses can reliably come out of a single capacitor per second which has to produce 60 to 130 volts....granted @ mileamperes....but still at up to 180 pulses per second? O well, it seems the Capacitor has endured and the problem is the final coil. Sierra has a higher quality coil but they will not become available again until July.
 
180 pulses a second is nothing.

Electronics generally work in milliseconds (1000 times a second) or faster.

An electronic component performing a task for 2/1000's out of every second is like you and me watching a clock to perform a one second task once a minute.
 
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