Tecumseh TC300 2-stroke has a weak spark - HobbyTalk
 
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post #1 of 6 (permalink) Old 09-19-2007, 08:45 PM Thread Starter
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Tecumseh TC300 2-stroke has a weak spark

Tecumseh 50cc 2-stroke has a weak spark. You can only see the spark in dim or darkened room. The ignition system consists of only solid state ignition module, flywheel magnets and spark plug. The ignition module has been replaced, and other spark plugs have been tried. The magnets appear to be strong, and I tried disconnecting the kill switch. My experience with other engines, including 2-stroke motocross bikes, lead me to believe I should have a much stronger blue spark with an audible snap, snap, snap. Thanks for any ideas.
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post #2 of 6 (permalink) Old 09-19-2007, 08:49 PM
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as long at it is a nice blue color, the spark should be fine

but just to make sure, be sure you have the air gap between the flywheel and the coil set to .010
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post #3 of 6 (permalink) Old 09-19-2007, 09:23 PM
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It does not matter what color the spark is, that does not tell you anything about the intensity of the spark! Isolate the kill switch, make sure the coil/module has a clean and good ground and use a spark tester to see if it will jump a larger air gap.

Here is an excerpt from an article about ignition systems from the Briggs and Stratton website. Although you have a Tecumseh engine all ignitions work on the same principle.

Now, how about some of those old wives tales that just aren't true.

* Rust on the flywheel magnets causes a loss of spark. Not true. A magnetic field does not care about rust. It has no effect on it.
* A bright blue spark is best. A yellow/orange spark signifies weak ignition. 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.
* Laying the spark plug against the block and pulling the engine over can adequately test ignition coil output. Not true. The ignition coil will only generate enough output to jump the gap of the plug. When under compression, the plug requires twice the voltage to fire. This check is not an accurate test of the coil and can be misleading.
* An armature air gap that is too wide will prevent spark. Not true. Well, sort of not true. Briggs & Stratton air gaps cannot be made too wide to prevent spark providing the coil is healthy and the engine is spun over fast enough. A wide air gap, say .030" will ever so slightly retard the ignition timing as the magnetic field takes longer to build within the coil windings.

Last edited by 30yearTech; 09-19-2007 at 09:23 PM.
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post #4 of 6 (permalink) Old 09-20-2007, 08:26 AM
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If placing the spark plug to the block and seeing if there is a spark, is not a good way to test the coil, what is? What will tell if you have a weak coil. I have been told the coil either works or it does not. I have found this to be false. You can have a weak coil.

Russ.
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post #5 of 6 (permalink) Old 09-20-2007, 09:22 AM
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Quote:
Originally Posted by RKDOC
If placing the spark plug to the block and seeing if there is a spark, is not a good way to test the coil, what is? What will tell if you have a weak coil. I have been told the coil either works or it does not. I have found this to be false. You can have a weak coil.

Russ.
It's an alright way to test for spark, but it won't tell you anything about the intensity of the spark.

Solid State modules generally fail due to a faulty trigging device and not because of the coil, in this case they either work or they don't.

Yes, you are correct you can have a weak coil. Test the spark with a spark tester, you are jumping an air gap with at least a 1/2" of clearance, if the coil is strong enough for the spark to jump the wide air gap it, should work fine at the air gap spark plugs use .030". A lot of time when I test spark, I cannot see it jump the gap, but I can hear the "pop" that it makes when it does. The spark is sometimes very hard to see in the bright sunlight.

Last edited by 30yearTech; 09-20-2007 at 09:32 AM.
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post #6 of 6 (permalink) Old 09-20-2007, 11:49 PM
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Quote:
Originally Posted by 30yearTech
It does not matter what color the spark is, that does not tell you anything about the intensity of the spark! Isolate the kill switch, make sure the coil/module has a clean and good ground and use a spark tester to see if it will jump a larger air gap.

Here is an excerpt from an article about ignition systems from the Briggs and Stratton website. Although you have a Tecumseh engine all ignitions work on the same principle.

Now, how about some of those old wives tales that just aren't true.

* Rust on the flywheel magnets causes a loss of spark. Not true. A magnetic field does not care about rust. It has no effect on it.
* A bright blue spark is best. A yellow/orange spark signifies weak ignition. 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.
* Laying the spark plug against the block and pulling the engine over can adequately test ignition coil output. Not true. The ignition coil will only generate enough output to jump the gap of the plug. When under compression, the plug requires twice the voltage to fire. This check is not an accurate test of the coil and can be misleading.
* An armature air gap that is too wide will prevent spark. Not true. Well, sort of not true. Briggs & Stratton air gaps cannot be made too wide to prevent spark providing the coil is healthy and the engine is spun over fast enough. A wide air gap, say .030" will ever so slightly retard the ignition timing as the magnetic field takes longer to build within the coil windings.

thats actually very interesting
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