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What am I missing?
#1
M
Miles2112
M
Miles2112
Okay, I was getting the ol' mower out to do my bi-annual maintenance and It wouldn't start. It turns over but no combustion. So, first I changed out the Gas and put fresh fuel in, no go... So I checked the plug to see if it was getting fire. nada. No spark. I checked all of the safety switches and everything was okay. So.. I decided to pull off the housing and check out the Coil. There was some considerable rust on both the coil and the flywheel so I took a wire brush, cleaned the flywheel, took off the coil and cleaned it. Put it back on, and tried, and still no spark. So.. I tried taking off the grounding kill wire from the coil and still no spark.. I even bought a new spark plug and a new coil and set the gap just right and STILL!!! No spark. The last thing I tried was checking the magnet and it seemed strong. It held the flathead screwdriver in place even when I let go...
I'm stumped. Any thoughts? It's a LT 4200 Huskee with a Briggs and Stratton 18.5 Hspwr.
Miles
I'm stumped. Any thoughts? It's a LT 4200 Huskee with a Briggs and Stratton 18.5 Hspwr.
Miles
#2
Fish
Fish
Just guessing that your "no spark" thing is wrong. Likely the carb is full of moisture.
Post the complete engine model numbers.
Post the complete engine model numbers.
#3
M
Miles2112
M
Miles2112
This isn't about the carburetor. I'm explaining that the coil is not producing a spark. The spark plug is grounded to the chassis. Have you ever tested a spark plug to see if it's getting spark in that way?
#4
S
Selluwud
Bad plug wire??
S
Selluwud
Okay, I was getting the ol' mower out to do my bi-annual maintenance and It wouldn't start. It turns over but no combustion. So, first I changed out the Gas and put fresh fuel in, no go... So I checked the plug to see if it was getting fire. nada. No spark. I checked all of the safety switches and everything was okay. So.. I decided to pull off the housing and check out the Coil. There was some considerable rust on both the coil and the flywheel so I took a wire brush, cleaned the flywheel, took off the coil and cleaned it. Put it back on, and tried, and still no spark. So.. I tried taking off the grounding kill wire from the coil and still no spark.. I even bought a new spark plug and a new coil and set the gap just right and STILL!!! No spark. The last thing I tried was checking the magnet and it seemed strong. It held the flathead screwdriver in place even when I let go...
I'm stumped. Any thoughts? It's a LT 4200 Huskee with a Briggs and Stratton 18.5 Hspwr.
Miles
Bad plug wire??
#5
Fish
Fish
With the kill wire removed, the coil will fire, if the flywheel is rotated fast enough.
If not, then the coil is bad.
But you replaced the coil..
Unless the new coil is bad, or you destroyed the new coil by somehow sending voltage to the kill wire {possible}.
Only other possibilty is a bad flywheel {magnets}, but I have never seen one.
If not, then the coil is bad.
But you replaced the coil..
Unless the new coil is bad, or you destroyed the new coil by somehow sending voltage to the kill wire {possible}.
Only other possibilty is a bad flywheel {magnets}, but I have never seen one.
#6
B
bertsmobile1
B
bertsmobile1
Fish has nailed it.
Remove the kill wire from the coil then check it for voltage when you turn the mower on & off and when the engine is cranked.
Any voltage on it and you will destroy the hall effect trigger chip in the magneto.
If you have bought cheap parts from ebay or Amazon then there is a good chance you could have gotten a deffective coil.
Remember China buys the USA trash but they don't make any trash themselves, everything that comes off the machines gets sold , working or not.
Hall effect trigger chips are very easily damaged.
A $ 20 harbour Freight meter can fry them and don't even ask about the trash sold at Walmart.
Rust on a magnet does not affect the magnet, did you not do any physics at school ?
The caveat is if the rust is thick enough for the coil to touch the magnet.
Where a good clean contact is needed is between the coil and the mower where it grounds.
Permanent magnet magnetos are self energising so the faster the magnet passes the coil the higher the voltage and the better the spark.
Something you should have been taught in school again.
At cranking speeds the spark can be very hard to see So I always suggest, and use myself a red tube spark tester.
Low voltages can dribble down the sides of the center electrode in the plug so you will never see feint blue against white porcelain.
Go slow enough and the voltage generated by the coil will be less than the internal resistance of the coil so there will be no spark.
So if there is a good coil, and if it is grounded properly and if the magnets have any flux left and if the plug is grounded then you have to get a spark.
Remove the kill wire from the coil then check it for voltage when you turn the mower on & off and when the engine is cranked.
Any voltage on it and you will destroy the hall effect trigger chip in the magneto.
If you have bought cheap parts from ebay or Amazon then there is a good chance you could have gotten a deffective coil.
Remember China buys the USA trash but they don't make any trash themselves, everything that comes off the machines gets sold , working or not.
Hall effect trigger chips are very easily damaged.
A $ 20 harbour Freight meter can fry them and don't even ask about the trash sold at Walmart.
Rust on a magnet does not affect the magnet, did you not do any physics at school ?
The caveat is if the rust is thick enough for the coil to touch the magnet.
Where a good clean contact is needed is between the coil and the mower where it grounds.
Permanent magnet magnetos are self energising so the faster the magnet passes the coil the higher the voltage and the better the spark.
Something you should have been taught in school again.
At cranking speeds the spark can be very hard to see So I always suggest, and use myself a red tube spark tester.
Low voltages can dribble down the sides of the center electrode in the plug so you will never see feint blue against white porcelain.
Go slow enough and the voltage generated by the coil will be less than the internal resistance of the coil so there will be no spark.
So if there is a good coil, and if it is grounded properly and if the magnets have any flux left and if the plug is grounded then you have to get a spark.
#7
M
Miles2112
M
Miles2112
I am guessing that Australian schools are more advanced than the small town I grew up in. We did not have a physics class. Of course, this was back in 1985. I appreciate the helpful advice but not sure why it warrants scoffing. I mean, we are only talking about a lawnmower not the effect of magnetic fields on the stability of a cylindrical flow with mass and heat transfer or any other quantum machanics theories. I only brought this to the forum because it is baffeling. In all essence the system should be producing a spark unless all three coils I have tried are bad. The speed of rotation is determined by the starter since that is what I am using to crank the motor. I was hoping to get advice about anything I might have not tried. I have a Fluke Multimeter that costs me about $200. Being an electrician, I cleaned the rust out of habit, not because I thought it wouldn't work otherwise. I have worked on this machine several times and have always been able to see the spark when diagnosing problems. This is the first time ever that I have not been able to produce one through the plug. If it wasn't out of the ordinary, I wouldn't have brought it here.
I will try to get it to the lawn mower guy who sold me the last coil and see if he can figure it out.
M.
I will try to get it to the lawn mower guy who sold me the last coil and see if he can figure it out.
M.
#8
T
Tinkerer200
If you really want to check it, stick a Philips screw driver in the spark plug boot, grasp the screw driver by the shank, touch your finger to a bare spot on the engine and hit the starter. A sissy way of doing it is remove the spark plug, turn the flywheel so magnet is close to coil then twirl the flywheel hard by hand holding the screw driver as described above. Do that and I won't have to explain how to tell if coil is bad. Well if you are still holding the screw driver, coil is bad.
Walt Conner
T
Tinkerer200
This isn't about the carburetor. I'm explaining that the coil is not producing a spark. The spark plug is grounded to the chassis. Have you ever tested a spark plug to see if it's getting spark in that way?
If you really want to check it, stick a Philips screw driver in the spark plug boot, grasp the screw driver by the shank, touch your finger to a bare spot on the engine and hit the starter. A sissy way of doing it is remove the spark plug, turn the flywheel so magnet is close to coil then twirl the flywheel hard by hand holding the screw driver as described above. Do that and I won't have to explain how to tell if coil is bad. Well if you are still holding the screw driver, coil is bad.
Walt Conner
#9
Fish
Fish
Leave it all set up to test the spark, then tonight, after dark, go out in the dark and crank it again.
I am betting that you will see a spark.
I am betting that you will see a spark.
#10
B
bertsmobile1
B
bertsmobile1
You know who you are , what expertese you have and what tools you are using.
We know only what is typed on the screen.
As you made specific mention about doing something that is totally useless like wire brushing the flywheel the assumption is you have less than no idea about what you are doing.
Also a lot of people search through these threads looking for answers and never post themselves.
Thus it is important to make people have a little think and realise that the stuff they should have been taught actually applies to real life.
And most of the people who post are using gear they bought at HF or Wallys and have no idea of how to use it thus they post stuff like 3.975 ohms.
So answers get pitched to the level of expertese shown in the persons post.
Now getting back to your mower.
1) where did you get the magneto modules that are not creating a spark ?
2) have you checked the trigger wire for stray voltage.
I had a mower where there was a short in one of the safety switches so cranking voltage was being sent down the kill wire.
I lost 2 magneto modules to that mower before I checked the kill wire. So a change is SOP happened & the kill wire gets checked before any module is replaced.
An electrician should understand the consequences of pumping 12 V down a ground wire to a chip that has transistors which switch in the milli volt range and can only handle milli amps.
The only other 2 possibilities are the module was installed up side down thus reversing the polarity
Or the plug was bad out the box and it has an internal short or the potential is grounding down the insulator and not jumping the gap.
The insulator on the center electrode on spark plugs is no longer glazed and I should not have to tell an electrician the difference in surface resistance between a glazed & unglazed insulator.
Further more being unglazed they can easily be damaged and leave metal tracks if carelessly gapped or cleaned with a wire brush .
The stuff we have to use now days in place of petrol is very conductive at cylinder pressures and once it deposits a conductive film on a plug, that film can only be burned off .
The cranking spark is quite low energy so is generally weak & can be very hard to see which is why I use a red glowing neon tube spark tester
So you can also hook up your meter to the secondary coil windings the crank the engine and bring up the memory of the highest voltage.
We know only what is typed on the screen.
As you made specific mention about doing something that is totally useless like wire brushing the flywheel the assumption is you have less than no idea about what you are doing.
Also a lot of people search through these threads looking for answers and never post themselves.
Thus it is important to make people have a little think and realise that the stuff they should have been taught actually applies to real life.
And most of the people who post are using gear they bought at HF or Wallys and have no idea of how to use it thus they post stuff like 3.975 ohms.
So answers get pitched to the level of expertese shown in the persons post.
Now getting back to your mower.
1) where did you get the magneto modules that are not creating a spark ?
2) have you checked the trigger wire for stray voltage.
I had a mower where there was a short in one of the safety switches so cranking voltage was being sent down the kill wire.
I lost 2 magneto modules to that mower before I checked the kill wire. So a change is SOP happened & the kill wire gets checked before any module is replaced.
An electrician should understand the consequences of pumping 12 V down a ground wire to a chip that has transistors which switch in the milli volt range and can only handle milli amps.
The only other 2 possibilities are the module was installed up side down thus reversing the polarity
Or the plug was bad out the box and it has an internal short or the potential is grounding down the insulator and not jumping the gap.
The insulator on the center electrode on spark plugs is no longer glazed and I should not have to tell an electrician the difference in surface resistance between a glazed & unglazed insulator.
Further more being unglazed they can easily be damaged and leave metal tracks if carelessly gapped or cleaned with a wire brush .
The stuff we have to use now days in place of petrol is very conductive at cylinder pressures and once it deposits a conductive film on a plug, that film can only be burned off .
The cranking spark is quite low energy so is generally weak & can be very hard to see which is why I use a red glowing neon tube spark tester
So you can also hook up your meter to the secondary coil windings the crank the engine and bring up the memory of the highest voltage.
#11
Fish
Fish
Another possibility is that the original ignition is fine.
That is the most likely thing.
Draining out the carb's gas/water mix likely would have fixed it. Or else, going through the fuel system first.
But, one jumps to a conclusion, and has to stick with it, no matter what!
Pride takes over quickly...
That is the most likely thing.
Draining out the carb's gas/water mix likely would have fixed it. Or else, going through the fuel system first.
But, one jumps to a conclusion, and has to stick with it, no matter what!
Pride takes over quickly...