Troy-Bilt/Briggs Won't Start/No Spark

NeedAFix

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Two weeks ago I sought help from a different online forum. In an effort to divulge all that was considered on that forum I submit the web address for consideration.
https://www.lawnsite.com/threads/troy-bilt-briggs-wont-start.484327/
I used the suggestions provided and still have no spark.
Hopefully someone here will be able to suggest something that has not yet been tried.
 

ILENGINE

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The test for bad coil is to remove the ground wire/Kill wire from the tab on the coil, and with a known good plug crank the engine. If no spark replace the coil, if you have spark then something is wrong with the kill wire or the kill switch. Can't really test the new coils with a ohm meter because of the electronics inside don't allow for that to work properly, and in some cases the voltage generated by the battery in the meter can actually destroy the electronic trigger inside the coil
 

NeedAFix

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In regard to "remove the ground wire/Kill wire from the tab on the coil, and with a known good plug crank the engine. If no spark replace the coil," That is one of the things that I did do. I did not know that a new coil can't be ohm tested. Perhaps that suggests that the out-of-spec high end reading is irrelevant? However, with a new coil properly mounted on the engine there still is no spark.
 
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Magnets on the flywheel can go bad creating your issue..... Take a 1/2 inch combo wrench and put it near the magnet.

See how far from the mag it pulls..........
 

NeedAFix

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I applied the recommended wrench test: At approximately one inch from the flywheel the wrench is pulled strongly into the wheel.

This morning the coil seller offered a return of both new coils for a refund. Although I get ohm readings exceeding the high end of the supposed spec of 5.0K at the 20K ohms setting I'm reluctant to return them until I can definitely determine why I get no spark.

I'm hoping someone will have a solution. Should it be something other than the coil perhaps the old coil is usable. It has a bench test reading of 4.31K ohms which is near the high end and that is why it was previously recommended that I replace it.
 

bertsmobile1

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Well this is how the system works.
Remember the old days when you had points ?
The points simply made & broke the ground connection to the coil to prevent the voltage generated by the moving magnet being released till the piston was in the correct place.
Well the voltage generated in the coil is not an on/off event, it starts at 0 volts, goes up to around 1500V then drops off to 0 again.
In 1962 a mob down here realised you could measure the voltage rising in the coil and electronically make & break the ground contact.
It is called a Hall Effect Trigger ( google it ).
Atom marketed them for 30 years till the patient expired then every engine maker that was too cheap ( Briggs & Tecumseh ) to pay Atom royalties made their own trigger.
Fist off they were small circuit boards , around the size of a postage stamp & 1/8" thick & were fitted externally.
You can still buy them like that and these last almost forever.
However engine companies worked out the tiny circuit board which cost around $ 2 could be replace with a chip embeded into the coil which costs around 10¢.
This also makes the coil & trigger 1 item which reduces the assembly & inventory costs .
It also allows them to charge up to $ 100 for a $ 10 item because it is now unique and not repairable.
The voltages measured are tiny and the current is even tinier still so a cheap OHM meter shoves current down the probes and measures the drop in the return voltage and uses Ohm's Law ( google it ) to convert voltage drop into resistance .
Thus taking an Ohm reading on the primary side can destroy the control chip.
Now you can measure the secondary resistance, because the coil is also a transformer and has 2 sets of windings, a primary ( has the chip on it ) & the secondary ( has the spark plug on it ).
However as it is a single unit & not repairable measuring anything on it just wastes time & proves you have no idea about how the magneto module actually works.
You only do 2 tests on a magneto.
1) remove the kill wire
2) tug on the spark plug boot to confirm it is actually connected.

Because the system works on magnetism & magnetism travels through rust, paper, wood, earth etc etc removing rust will make zero difference to a magneto unless it is so thick the coil legs actually touch the magnets, but that willbe visually apparent because there will be scrape marks o the magnets.
So the instant some one starts talking about cleaning the rust off, you can forget about anything they say cause they are just keyboard clowns regurgitating the rubbish some equally as scientifically ignorant moron has been sprouting on the web in order to make themselves look important / smart etc.

Now back to your problem.
Without the ground wire connected and if the coils themselves have a good ground ( clean where that contact the mounts ) then it either generates a spark or it dont so as previously mentioned it works or it gets replaced.
Different coils have different chips in them so in most cases they are not interchangable regardless of weather they make a spark or not.

Finally.
The only scrap in China is what they import to reprocess or salvage.
So parts made by the OEM supplier to Briggs / Kohler / Honda that fail quality control get on sold to surplus wholesalers ( along with genuine surpluses ) and ultimately sold to cheapskates via ebay amazon etc.
OEM does not mean works it simply means it came out of the same factory.
I can buy coils direct from China for $ 5 or from Hong Kong for $ 5 to $ $20, but I pay $ 40 to get identical looking ones from my wholesale supplier because these are the ones that work properly.
 

bertsmobile1

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And as for different forums.
I bought the service run 5 years ago and being fairly at home around small engines thought it would be a breeze.
It wasn't so i joined every forum, group or sewing circle in any way connected to mower, trimmer & chain saws ( some of the arbourist sites are really worrying ) .
Now I do not like to bad mouth people who are doing things with good intentions.
However there was only one place that consistantly had good & more importantly correct information, and you are reading this post on it.
Others did have value including archives of service information which was very helpful & where possible I added to them.
But when it comes to getting a currently used mower back up & running this site is head & shoulders above anything else on the web.
If you are restoring an ancheint mower for the fun of it & not particularly to use then Mymower forum would in general be a better place and of course single brand sites.
 

NeedAFix

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I appreciate the thorough commentary in this regard. After all of what I have tried I am still uncertain as to whether the coil is positively 100% the cause of the problem. The old original coil has a resistance reading (4.31K) that is near the high end of suggested specs (2.5K to 5.0K) so it was recommended that I try a new one. $58 U.S. (at ereplacementparts) is a high price to pay for a part that might not even solve the problem. For me, the $12 I spent for an aftermarket part was worth the risk. I have no way of knowing whether the coils from China were defective, especially since you debunked the resistance testing that I did which I depended on for factual resistance readings. Not being familiar with small engine repair I had hoped to learn by doing and economically be able to revive the very old mower.
 

SidecarFlip

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Bert..

Don't forget to add that Hall effect sensors are all over automobiles, from the rear end (speedometer sensors) to the engine ECM triggers to the brakes, ABS sensors.
 

NeedAFix

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How or why is this in anyway related to this thread?
 
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