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I have a 6.5hp briggs on a poulan pro mower. The coil will spark a few times and quit, spark and quit.

#1

M

moodymac

I have disconnected the ground wire with no effect. Tried a new coil from another project (same coil type) and got the same results. I cleaned all contact points on both the mower and old coil. Set both coils to .012 inches. Ran ohm test on old coil (4.3) and new coil (6). Checked magnet on flywheel, and it seemed strong, however I know of no other way of testing it. Ran ohm test on ground wire and got no resistance. The brake switch was open when in run and closed when off. Am stumped, any help would be appreciated.


#2

Scrubcadet10

Scrubcadet10

what method are you using to check spark?


#3

R

Rivets

Sounds like you may have a bad ground. Please post all engine numbers. What did you set the point gap at?


#4

StarTech

StarTech

Good question as if using the same old plug it might be defective. Always use a known good. New doesn't always mean good plug.


#5

M

moodymac

I checked the spark with an inline spark meter (light). Turned the engine over with spark plug out and connected to the spark indicator. With a separate jumper wire run from the engine to the plug for the ground. The coils were checked with an ohm meter set at 20k. Complaint was the engine either would not start, or occasionally started then immediately died. The new coil on hand acted the same as the original. The new plug acted the same as the original. The ground wire to the coil was at first connected and then disconnected with no difference. The engine is a Briggs Quantum on a Poulan Pro self-propelled push mower. The spark tester shows spark when I first start the rotation of the flywheel, then quits. It starts back if I quit and restart the rotation, then quits again. The spark last anywhere from one to three seconds. Could it be the flywheel itself? How do I check it other than to see if iron sticks to the magnet?


#6

R

Rivets

I’d set the armature air gap to .008 and see if there is any change. Very seldom do magnets go bad. Finally, checking resistance on today’s coils is meaningless, as they contain Hall effect triggers which you need high tech equipment to check.


#7

Fish

Fish

Are you spinning the flywheel with a drill, or using the pull starter?


#8

M

moodymac

Rivets said:
I’d set the armature air gap to .008 and see if there is any change. Very seldom do magnets go bad. Finally, checking resistance on today’s coils is meaningless, as they contain Hall effect triggers which you need high tech equipment to check.
Click to expand...
I reset the gap to .008 and no change. Put the new coil on the machine I had purchased it for, and it works perfect. Also used the spark plug on the bad machine, and it also works perfectly on this one. And I recheck the pull of the magnets on both machines together, and they appeared to have the same strength.


#9

M

moodymac

Fish said:
Are you spinning the flywheel with a drill, or using the pull starter?
Click to expand...
Both.


#10

R

Rivets

When you say “works perfect”, does that mean problem solved?


#11

Scrubcadet10

Scrubcadet10

I think he means he had purchased a new coil for another machine, that works on it. but not on his problem engine.


#12

M

moodymac

moodymac said:
Both.
Click to expand...
No, the machine which worked perfect was working on the parts (coil and plug) which tested bad on the above machine. When tried on this machine, it had no spark and of course would not start. Something is causing the coil to miss-fire. I ran down the ground kill switch, tested the ground wire, and disconnected the ground wire at the coil, and it still would only make intermediate sparks. Just to make sure I was not dealing with two bad coils (the original coil and the new one), I tried it on another engine. It showed spark on the tester and the engine started and ran. I still do not know what is causing the coil to miss-fire on the engine in question.


#13

M

moodymac

Scrubcadet10 said:
I think he means he had purchased a new coil for another machine, that works on it. but not on his problem engine.
Click to expand...
Rivets said:
When you say “works perfect”, does that mean problem solved?
Click to expand...
No, the machine which worked perfect was working on the parts (coil and plug) which tested bad on the above machine. When tried on this machine, it had no spark and of course would not start. Something is causing the coil to miss-fire. I ran down the ground kill switch, tested the ground wire, and disconnected the ground wire at the coil, and it still would only make intermediate sparks. Just to make sure I was not dealing with two bad coils (the original coil and the new one), I tried it on another engine. It showed spark on the tester and the engine started and ran. I still do not know what is causing the coil to miss-fire on the engine in question.


#14

M

moodymac

Scrubcadet10 said:
I think he means he had purchased a new coil for another machine, that works on it. but not on his problem engine.
Click to expand...
Correct.


#15

M

moodymac

Rivets said:
When you say “works perfect”, does that mean problem solved?
Click to expand...
No, the machine which worked perfect was working on the parts (coil and plug) which tested bad on the above machine. When tried on this machine, it had no spark and of course would not start. Something is causing the coil to miss-fire. I ran down the ground kill switch, tested the ground wire, and disconnected the ground wire at the coil, and it still would only make intermediate sparks. Just to make sure I was not dealing with two bad coils (the original coil and the new one), I tried it on another engine. It showed spark on the tester and the engine started and ran. I still do not know what is causing the coil to miss-fire on the engine in question.


#16

A

artemjemmy

Rivets said:
I’d set the armature air gap to .008 and see if there is any change. Very seldom do magnets go bad. Finally, checking resistance on today’s coils is meaningless, as they contain Hall effect triggers which you need high tech equipment to check.
Click to expand...
There are a huge variety of different methods for creating spark on small engines. Briggs uses the magetron setup with a trigger coil and a darlington transistor, tecumseh used a basic CDI method, and others like stihl have microprocessors in their magentos to limit top-end RPM. There was also the kohler DSAI modules, and the kohler SAM system, (both of which were so bad that kohler discontinued them). This sort of stuff is very interesting to me and I want to know more about the circuitry in these modules, but removing the epoxy is very difficult.


#17

M

moodymac

artemjemmy said:
There are a huge variety of different methods for creating spark on small engines. Briggs uses the magetron setup with a trigger coil and a darlington transistor, tecumseh used a basic CDI method, and others like stihl have microprocessors in their magentos to limit top-end RPM. There was also the kohler DSAI modules, and the kohler SAM system, (both of which were so bad that kohler discontinued them). This sort of stuff is very interesting to me and I want to know more about the circuitry in these modules, but removing the epoxy is very difficult.
Click to expand...
Interesting. Where is the Darlington transistor located? Could this be the cause of intermittent spark?


#18

A

artemjemmy

moodymac said:
Interesting. Where is the Darlington transistor located? Could this be the cause of intermittent spark?
Click to expand...
If I recall correctly, the darlington transistor is "turned on" by the magnetron-branded trigger coil, and when the transistor is on, it allows current to build in the primary winding.


#19

M

moodymac

artemjemmy said:
If I recall correctly, the darlington transistor is "turned on" by the magnetron-branded trigger coil, and when the transistor is on, it allows current to build in the primary winding.
Click to expand...
Yes, I just read up on it. It is located within the coil itself. This could not be my problem due to the fact of the coil not working properly on the problem machine, yet working just fine on another. My guess right now is it has to be the flywheel. Somehow it is capable of sending enough magnetic force causing a spark for just a few revolutions of the wheel. When the flywheel comes to rest, it regains this energy. If I had another flywheel on hand, I would test this theory.


#20

Scrubcadet10

Scrubcadet10

moodymac said:
Yes, I just read up on it. It is located within the coil itself. This could not be my problem due to the fact of the coil not working properly on the problem machine, yet working just fine on another. My guess right now is it has to be the flywheel. Somehow it is capable of sending enough magnetic force causing a spark for just a few revolutions of the wheel. When the flywheel comes to rest, it regains this energy. If I had another flywheel on hand, I would test this theory.
Click to expand...
could you swap over the flywheel from the other machine? it can take some effort if you need a puller, but it may be worth a shot?


#21

M

moodymac

Scrubcadet10 said:
could you swap over the flywheel from the other machine? it can take some effort if you need a puller, but it may be worth a shot?
Click to expand...
No, they share some common parts, but the flywheels are different.


#22

R

Rivets

If the flywheels are different, then the coils may be different??? How about posting all engine numbers from both units, so we can do some investigating deeper.


#23

M

moodymac

Rivets said:
If the flywheels are different, then the coils may be different??? How about posting all engine numbers from both units, so we can do some investigating deeper.
Click to expand...
120k02-0418-e-1 on the Murray 22 in walk behind trimmer I just happened to be rebuilding (and was waiting on parts for) when I started working on 123k-0217-e1 the Poulan Pro lawn mower (problem machine). Both the original coil on the Poulan, and the new coil, are the same. Both failed to produce consistent spark on the Poulan, but both worked on the Murray.


#24

R

Rivets

First, the second number should be 123K02. Both engines use the same coil and flywheel. Coil number should be 590454. Have you removed and checked the flywheel key?


#25

M

moodymac

Rivets said:
First, the second number should be 123K02. Both engines use the same coil and flywheel. Coil number should be 590454. Have you removed and checked the flywheel key?
Click to expand...
No, however, on visual inspection the flywheel and crank slots are exactly lined up, and the key is in place.


#26

StarTech

StarTech

According to the IPLs both engine should have the same flywheel PN 691987. IF they are different that maybe the problem.


#27

B

bertsmobile1

Get a compass, a real one with a swinging needle, not your phone
Sit it on top of the coils & slowly rotate the flywheels ( check both engines )
I am hazarding a guess that the magnets on one have reversed or are compromised
As the flywheel passes the compass , the needle will swing either N ( showing the magnet is south out ) or S ( showing it is north out ) or will swing showing the magnet is orientated length wise ( not usual ) .
You can get a very rough measure of the strength by moving the compass back and seeing how far away the flywheel moves the compass needle
From what you have posted to date, using substitution to draw a conclusion the flywheel is the problem.

Magnets loose power over time, loose power with exposure to heat , loose power with exposure to mechanical actions like hammering or with mower engine rubbing on the coil legs .
Coils get hot during use , heat increases the resistance of the coil and if the magnet is marginal to start with then after a few revolutions it could end up being outside the operating range .


#28

R

Rivets

According to the numbers you posted they both use the same flywheel. Seeing you have two different flywheels, have you checked to see if everything is exactly the same? Magnet location in relation to key slot.slot, Flywheel diameter, Magnet size, etc. As stated I think you’ve found your problem


#29

B

bertsmobile1

And are you sure the blower housing with the model number on it belongs to the engine it is on.
More than once I have been caught out because the covers had been swapped and what was under the hood was not the original engine.


#30

M

moodymac

StarTech said:
According to the IPLs both engine should have the same flywheel PN 691987. IF they are different that maybe the problem.
Click to expand...


#31

M

moodymac

The diameter is the same, but the cooling fins are much taller and pronounce on the Poulan vs the Murray and would not allow for the top cover to be refitted. Besides, the customer is picking up the Murray soon.


#32

M

moodymac

bertsmobile1 said:
And are you sure the blower housing with the model number on it belongs to the engine it is on.
More than once I have been caught out because the covers had been swapped and what was under the hood was not the original engine.
Click to expand...
Yes, both are original.


#33

M

moodymac

Rivets said:
According to the numbers you posted they both use the same flywheel. Seeing you have two different flywheels, have you checked to see if everything is exactly the same? Magnet location in relation to key slot.slot, Flywheel diameter, Magnet size, etc. As stated I think you’ve found your problem
Click to expand...
Yes, the only visible difference that I can see are the cooling fins. I have a couple of locked up Briggs engines, tomorrow I will check the flywheels and try replacing the one on the problem engine.


#34

M

moodymac

bertsmobile1 said:
Get a compass, a real one with a swinging needle, not your phone
Sit it on top of the coils & slowly rotate the flywheels ( check both engines )
I am hazarding a guess that the magnets on one have reversed or are compromised
As the flywheel passes the compass , the needle will swing either N ( showing the magnet is south out ) or S ( showing it is north out ) or will swing showing the magnet is orientated length wise ( not usual ) .
You can get a very rough measure of the strength by moving the compass back and seeing how far away the flywheel moves the compass needle
From what you have posted to date, using substitution to draw a conclusion the flywheel is the problem.

Magnets loose power over time, loose power with exposure to heat , loose power with exposure to mechanical actions like hammering or with mower engine rubbing on the coil legs .
Coils get hot during use , heat increases the resistance of the coil and if the magnet is marginal to start with then after a few revolutions it could end up being outside the operating range .
Click to expand...
That sounds interesting, I will try to find my old compass and give it a try. Sounds like a good way to measure comparative magnetic strength.


#35

B

bertsmobile1

moodymac said:
That sounds interesting, I will try to find my old compass and give it a try. Sounds like a good way to measure comparative magnetic strength.
Click to expand...
Not as good as it sounds but I did find what I thought was a faulty old B & S engine only to find out much latter the magnets were supposed to be reversed so to get the module to work, you need to put it on upside down.
Depends upon the compass but it does sort of work a bit better than the "pulls a screwdriver from 1" away method .


#36

J

Joed756

bertsmobile1 said:
And are you sure the blower housing with the model number on it belongs to the engine it is on.
More than once I have been caught out because the covers had been swapped and what was under the hood was not the original engine.
Click to expand...
I'm very impressed you figured that problem out, I don't think I ever would have found it.


#37

B

bertsmobile1

I have just fitted a 406722 into a z435 that originally had a 44L777.
The owner wanted to retain the original blower housing so he could continue to buy the JD engine maintenace kits
So the bower says 23Hp JD but the engine is a 19Hp.
Very common for a customer to come in with a second hand mower and the blower housing is from a much bigger mower.
Funny you almost never see them the other way round .
A little more suspicious is when the Hp decal on the housing seems newer than the rest of the mower
Turn over an extra $ 200 for the cost of a $10 decal .


#38

M

moodymac

No, the cover is original. The gentleman that owns it owns seven self-propelled push mowers. He is a little eccentric, I have been servicing and maintaining them for years. I believe the problem is in the flywheel magnet. I have a source for a used flywheel, however the shop that it is at is closed due to COVID. It will be several days to wait to try it out. I will report back here with the results, thank you for helping.


#39

StarTech

StarTech

What Briggs might have done was to change the fan and shroud on the later engine as the IPLs shows the same PNs. It would not be the first time Briggs did this.


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