What should the spark look like with a timing light? 68 Sportwin 9.5

[moevinrude]

I am still fighting a mis. Hooked up an automotive timing light and noticed very erratic signal. Should it look like it would on a car or tractor, some pattern or rythym?

Also, I have noticed people on here having issues with spark and or fire and they are told to check compression, and or low idle jet on carb. Please correct me if I am wrong, but what does compression or carb work have to do with the fire at the plug? Just curious.

Thanks

 

[the machinist]

Re: What should the spark look like with a timing light? 68 Sportwin 9.5

Well, I will be the first to say that I am not a 9.5 expert & that I have never used a automotive timing light on a 2 cycle motor. What target on the flywheel are you using for the light to relate to? A simple spark tester used on each plug wire works for me.

However in answer to the question of spark/fire to compression. If your compression is low, you may not get enough to compress the fuel to the point that the spark may not ignite it. Basically resulting in a miss on that cyclinder. However the conscensus on compression testers is that many do not read the same, so if your compression is 80# plus the motor should run. I have seen some new rebuilds up to 120# on some testers & only 100# on a different tester.

Also if you have a weak spark, (could be a corroded or bad wiring connection somewhere) this could also contribute to the problem even if the compression is up. Even dirty points, or weak coils.

As for the firing of the plug, if the carb is not putting enough fuel into the cyclinders, the plug can not do it's job. Or if the plug is oil fouled it will not fire right. Then if the head has been Heli-Coiled because of stripped spark plug threads, the threaded insert may not be grounded good in the aluminum head, creating a non or intermittant firing spark plug.

 

[moevinrude]

Re: What should the spark look like with a timing light? 68 Sportwin 9.5

Thanks for the response. Let me clarify. I am using a timing light to check for proper spark, or fire going to the plug. The timing light, in theory, should light everytime there is a spark. So when the light is attached to either sparkplug wire, the timing light shows a fire that is not very consistent. It may signal or blink 4 to 5 times in a row, then not blink for 3 or 4. I wasn't totally sure if this was a possible way to check for fire. Thanks

 

[yorab]

Re: What should the spark look like with a timing light? 68 Sportwin 9.5

I would think that if the engine is running at a constant RPM, then the light should also light in a very constant, repeatable manner. Where are you hooking up the light?

 

[moevinrude]

Re: What should the spark look like with a timing light? 68 Sportwin 9.5

I am clamping to the sparkplug wire, close to the boot.

 

[moevinrude]

Re: What should the spark look like with a timing light? 68 Sportwin 9.5

The reason I tried this method was because this motor starts on first pull, idles great for the count of 10, then has a mis. The spark tester shows a blue spark, but doesn't show a constant fire when you pull start it. This seemed odd to me, so I just hooked up the timing light. Maybe it wasn't a good idea? One would only think is could work the same way as with your car.

 

[yorab]

Re: What should the spark look like with a timing light? 68 Sportwin 9.5

While the light won't tell you about the strength of the spark, it should give you an idea of it's consistency. So, either the voltage in the line is very erratic as you noted, or it is just at the threshold of what the light needs in order to fire. Therefore, the light will fire at times when the voltage is just above the threshold and won't fire at times when the voltage is just below the threshold.

A better way would be to use a spark tester. You can then test for consistency and strength of the spark. They are cheap and readily available at any auto parts place. Joe Reeves also has a post on the forum of how to easily make your own spark tester with a board, a few nails, and a bit of solder.

 

[Silvertip]

Re: What should the spark look like with a timing light? 68 Sportwin 9.5

You might want to check the battery connections and the clamp connection on the timing light as it may be the light giving you a problem and not the engine. If the engine is losing spark you would feel, hear, and see it on the engine as that cylinder began to misfire. This would be especially true if the problem was occuring on both cylinders and any misfire an a two cylinder engine is VERY noticable. Using a timing light on a two stroke is no different than on an auto engine. Spark makes light.

 

[moevinrude]

Re: What should the spark look like with a timing light? 68 Sportwin 9.5

I do feel the motor jump, and I do see it on the engine,,,,,,,,,,,,,,,,,,,this is why I have hooked up the timing light. The concerns I have with a spark tester is it only shows the spark itself, not the consistency. (unless there is one that does)

Could one guess an ignition problem if this motor starts easily, runs for 10 to 12 seconds with no problems, then starts to miss every 3 seconds? This is what drove me to trying the timiing light. To see if a misfire started after the 10 to 12 seconds. Thanks

 

[Silvertip]

Re: What should the spark look like with a timing light? 68 Sportwin 9.5

Spark testers DO indicate spark intensity because you can see the spark jump the gap. You do not see the spark with a timing light -- you see the result of the spark. The timing light merely sensing the presence of spark triggers circuitry inside the light that triggers the flash. If the lamp is triggered it is always same brilliance regardless how strong the spark is. As I said, if the spark is strong enough to trigger the circuitry the light will flash. That spark intensity threshold is really quite low.

 

[moevinrude]

Re: What should the spark look like with a timing light? 68 Sportwin 9.5

I may be confused.................when I do get a spark, using the old method of holding the plug close to the block, it is blue and jumps a 1/4 inch. But as I am watching for the spark as I pull on the rope, the motor appears to make several revolutions with minimal spark attemps. I thought the timing light would demonstrate how often the motor sparks, thus confirming an ignition problem.

 

[boobie]

Re: What should the spark look like with a timing light? 68 Sportwin 9.5

Have you had the flywheel off and checked your coils, points and condensers??