# 18 HP Briggs No spark



## riharley

18.5 HP Briggs NO SPARK 
I have a MTD tractor with 18.5 Briggs & Stratton Model 42A707 2238E1
Tractor stopped starting and then sat for over a year. 
1.	Found bad starter, changed it out. It now turns over 
2.	Magneto had frayed wire, changed it out . 
3.	Changed oil , plugs 
4.	Checked all ghorund connections, cleaned them
5.	Checked solenoid, it is working OK
6.	Battery charged

NO spark. It turns over, fuel is spurting out of top of carb (air cleaner off). Is this normal? 
I pulled left plug and laid it on head and turned over engine and saw no spark from plug. 
Any ideas what to change/check next? 

TIm 
Bristol, RI


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## dangeroustoys56

A little fuel might come up- excessive amounts is bad - id say the carb needs a cleaning/rebuild if needed.

On the magneto, you said there was a frayed wire? One of the spark plug wires or the magneto kill wire ( the small wire that hooks to the ign switch)? 

Id try unhooking the magneto kill wire and see if you have spark then ( you should) - it could be grounding out either before or at the ign switch ( time for a new ign switch).


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## riharley

Thanks for the help... 

The frayed wire was one of the spark plug wires to the Magneto. I changed out whole Mag with new plug wires attached. I'll try test and also make sure ground (kill wire) is making good connection. 
Bad ignition would let motor spin but interrupt spark?


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## riharley

Tried test by disconnecting black kill wire. and got no spark
The wire was the little black wire connected to magneto, right?


Also cleaned off magnet on flywheel. Still No spark. 
Is there a gap size for magneto to flywheel? could it be too close? 

Anything else to try?


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## jhngardner367

Hi,guys! Following the post,and I'm wondering if you set the armature(coil)air gap? Too large of a gap can cause no spark .


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## riharley

what should the gap be?


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## jhngardner367

Air gap should be .010/.012,between the flywheel,and the coil legs.Looosen the coil,and pull it away from the flywheel enough to insert a gauge(a strip of cardboard from a cereal box is .0124),then push the coil lightly against it,and tighten the screws.pull out the cardboard,and you're all set!


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## jhngardner367

I just realized some thing.the black wire from the coil----has it got a little eyelet?If so,it's the coil ground,and is held in place by one of the coil screws.Check the coil,near the sparkplug wire,for a small tab.That goes to the ign switch,and grounds out,to stop the engine,when the key is turned to off,and should have a push on connector.


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## riharley

set gap correctly. still no spark. Is it is possible that the new in box Magneto is bad?


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## dangeroustoys56

Its possible the new one could be bad . 

Usually when i set a magneto gap i leave the bolts loose, put a piece of oil filter box between the magneto/flywheel , spin the flywheel till the magnet lines up and snaps the magneto in place, tighten the mag bolts down and pull the cardbord out.

If theres no spark the motor will turn over all day and not fire up.

By the way- how old is the motor? It doesnt have points does it? The engine code's first two numbers are the motor's manufacture date. Youd tell if it had points by an extra wire running from the mag underneath the flywheel.


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## riharley

Model 424A707-2238E-1 Code 9908265B 
Are there points? I don't see points wire. 

I will try old Magneto and see it if works. 

to be contunued.....


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## riharley

*Stumped!*

Stumped. Still no spark. 

I have tried carefully setting magneto gap and swapped back the old magneto in case the new one was bad. Still no spark either way. 
NO spark with and without kill wire on magneto. 

What should I try next? Ignition switch? I'd really need to get this baby to run. 

Tim 
Bristol, RI


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## Mickey

Going WAY out on a limb here but how are the magnets in the flywheel?

Did some looking around and saw a pic of the mag kit. The pictue showed a button headed pin that is included. Did you get that with your new mag and what is it for?


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## riharley

Magnets are in good shape. I didn't get anything else in the magento box. Sorry still stumped. 

Can I push this tractor off a cliff now?


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## jhngardner367

Replace the coil.I think the new one is possibly bad,too.As DT56 said,it happens,sometimes!


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## riharley

Would you know how to check magneto/coil with a multimeter? Just to be on the same page, the magneto and the coil are the same thing, right? ...I'm not missing a separate coil somewhere?


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## Mickey

I think from common usage one can define the difference between the two. The word coil usually applies to battery powered ign systems and mag or magneto applies to self powered ign i.e. it produces its own primary power.

Using a multimeter to check the coil/mag is just a simple resistance reading. You need to know what the nom resistance reading is for both the primary and secondary windings. For sure you don't want to find dead shorts or infinite high resistance readings. With that said I don't have information on what the nom resistance is.

Looking at an old book I have but is new enough to cover the flat twins, if your engine has the magnatron ign system the air gap with the flywheel and ign module is .006-.010. If just the old mag style ign air gap is .010-.014.


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## Arkie

*same problem*

Same problem as thisa guy with same model Briggs engine.

Any ideas?


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## jhngardner367

By the way,guys,....make sure there's no rust/corrosion on the magneto legs,or the mount areas.
Also,(and please don't be offended,because it does happen),make sure the coil is on correctly,in that the side with the lettering is either up,or down,as it says on it .


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## jhngardner367

You also mention that fuel sprays out of the carb. Have you checked the flywheel key ? Even a small nick can change the timing.
Does it have an "oil-guard",in the crankcase? If so, disconnect it,and test for spark.


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## BENP

I have the same problems? any luck nothing is working with me about to take to professional


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## jhngardner367

Welcome to the forum,BENP .
What model engine do you have ?
Does it have a low-oil kill switch,on it?


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## willys55

if the key way on the flywheel is damaged in any way, it will not start or backfire....after reading through this entire thread I noticed that no one picked up on this.....I had three different mower with this same engine, and with two of them, the key way was the issue....it is soft aluminum and shears easily.


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## jhngardner367

A sheared key,will usually still give spark,...just not at the right time.
These guys are saying NO spark.
'


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## willys55

funny thing is, we are not there when they are checking for spark, they could be doing it wrong. I used a spark checker, one that I can set the gap, and one that is led and would light up even if a firefly triggered it........just stated that on the three I had, two needed the key way


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## jhngardner367

Very true,Doc,....should we have them hold the wire,to see??:lmao::lmao:


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## Arkie

willys55 said:


> if the key way on the flywheel is damaged in any way, it will not start or backfire....after reading through this entire thread I noticed that no one picked up on this.....I had three different mower with this same engine, and with two of them, the key way was the issue*....it is soft aluminum and shears easily*.


Old thread that has come alive!!!!!!!!!!!

Kinda surprised that
Several people I've talked too, some are supposedly mechanics and several I have not talked too do not know that a flywheel is suppose to be installed with the crank shaft taper and the flywheel taper completely dry and de-greased and then properly torqued and this friction fit is what is intended to hold/sieze the flywheel in place, not the flywheel key and the key is too only ensure that the flywheel is installed with correct engine timing. If a key is shearded for no immediate apparent reason I keep a heads up when inspecting/ removing the flywheel nut for proper torque and check that the crank and taper is free of lube.
I've seen steel keys installed instead of the soft aluminum key and cranks and flywheels ruined due to the steel key breaking the flywheel or crank slot before shearing or not shearing because Bubba lubed the crank so as he could remove the flywheel easier next time and installed a steel key to hold the flywheel in place and lightly tightened the flywheel nut so as the flywheel could be easier to remove next time if needed.

I've used them $15 china flea bay coils on the Briggs twins with good results, instead of the high dollar OEM Napa type coils.

I've seen the spark testers that use a light lie about spark, would light up and spark too weak.

I use the Briggs type spark tester that has the gap it has to jump or my homemade adjustable spark gap tester.

Also quite common for the Briggs twin coils to fail on one cylinder only also.


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## jhngardner367

Yep,...seen a lot of crazy,and downright stupid stuff,after havin' my shop,for near 20 years !! 
One I remember,was the guy that bought a brand new Sears tractor,and his neighbor convinced him they had the wrong plugs in it.
So, he swapped for some new Champion RC12YC6's,....and being a flat head it tore it up,when he tried to roll it over.
Tore the threads out of both heads,and ruined the valves.
He was angry at Sears because they wouldn't warranty it !
Or ,the guy that tried to put a long reach in his trimmer.....nasty.


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## Arkie

Back too that Briggs twin that was not firing.
No points in that one and a magneto type ign system and both coils is one case module. They have a electronic ckt inside and they cannot be checked with a ohmmeter like a regular coil. They are 2 independent circuits inside the same module and the module is directional for correct cylinder firing sequence. If the new coil is installed upside down the twin engine won't run.
Those type coil modules can be installed upside down and the spark will be non-existent or very weak. He can tell more about spark if he will remove both spark plugs and crAnk the engine with them grounded good, don't let the spark plugs just flop around on the end of their wires. I've used the $15 ebay ones on that type motor such as this one from flea bay.

152224559539 Also it's common for those engines to spray what looks like too much gas into the carb when they don't start. They will flood easily if they don't immediately start and remove the choke and advance the throttle wide open to get more air when cranking or5 let it sit for about 30 min's and then crank with the throttle wide open.You will see lots of spray into the carb throat when cranking and even when they are running. (normal thing)


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## willys55

I have not had much sleep the last few days so I may come off as a little blunt, however, on my twins, all 18 HP opposed cylinders...the coil fires both plugs on every revolution, it is called "waste spark" ignition. perhaps if we were talking about the the briggs 40 degree twin then it would be a different conclusion.


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## jhngardner367

willys55 said:


> I have not had much sleep the last few days so I may come off as a little blunt, however, on my twins, all 18 HP opposed cylinders...the coil fires both plugs on every revolution, it is called "waste spark" ignition. perhaps if we were talking about the the briggs 40 degree twin then it would be a different conclusion.


You are correct, Doc.


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## Arkie

willys55 said:


> I have not had much sleep the last few days so I may come off as a little blunt, however, on my twins, all 18 HP opposed cylinders...the coil fires both plugs on every revolution, it is called "waste spark" ignition. perhaps if we were talking about the the briggs 40 degree twin then it would be a different conclusion.


I thought the same about the MAGNETO coils on the old Briggs twins, waste spark and oriention of the MAGNETO should not make any difference,
*BUT try what I say and you will get a surprise.*
You flip the magneto upside down and connect the plug wires to their respective cylinders and she won't start or run. You will see a spark though. You can even reverse the plug wires and she still won't go. These type magnetos have two individual solid state ckt's inside for each individual coil. every once in awhile one will fial and only one cylinder firing also.

The old Onan points type engines with the waste spark coil ignition systems will run even reversed and I have used two automotive coils instead of one twin tower coil on them to get a run.


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## willys55

then you have a rare talent, because you can not mount this upside down


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## Arkie

Right. that OEM one is actually marked this side out and the plug wires are too short if mounted upside down. Even on yours it will still mount but the plug wires are too short when mounted upside down.

Most of the generic replacements are not marked this side out and the plug wires are long enough to reach easily if the coil is upside down the waste spark engine won't run with the magneto upside down.

Also have you ever tried running a waste spark engine with just one coil sparking both spark plugs at same time? (Both spark plug wires tied together so as to fire at same time from a single coil)


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## jhngardner367

I want to know how you got 2 automotive coils to work,since they're totally different systems.


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## willys55

Arkie said:


> Right. that OEM one is actually marked this side out and the plug wires are too short if mounted upside down. Even on yours it will still mount but the plug wires are too short when mounted upside down.
> 
> Most of the generic replacements are not marked this side out and the plug wires are long enough to reach easily if the coil is upside down the waste spark engine won't run with the magneto upside down.
> 
> Also have you ever tried running a waste spark engine with just one coil sparking both spark plugs at same time? (Both spark plug wires tied together so as to fire at same time from a single coil)


that is what the coil I posted does.........................reading is not one of your strong points


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## Arkie

jhngardner367 said:


> I want to know how you got 2 automotive coils to work,since they're totally different systems.


The onan waste spark system that I used two automotive coils on is not magneto, it's points system and uses a 12v battery for cranking or to power the coils.
These Onan engines were used on small welders and 4kw RV generators plus others.
The twin tower ONan coils (both coils built into one tower with two spark plug holes) are very expensive and I have used two Automotive type coils instead of the twin tower ONan coil in emergency's until the onan coil could be delivered. The Onan coils do not fail very often but when they do it's sadness on the pocket book. (and too expensive to keep a spare laying around)
Of course the automotive coils had to have the ballst resistors in the primary.

******* idea that flys: Works great, just takes up a lot of space.

Here is a4.0BFA RV gen onan engine on flea bay that uses the twin tower coil and waste spark points ignition and a picture of a similar coil

Onan 4.0BFA gen 282485943407

And Onan coil looks similar too this one on flea bay
222405721172

The coil cost's quite a bit more than this one on flea bay if you have (had) to go to Onan or their distributor before computer days.


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## jhngardner367

ONAN is a coil/battery ignition,not a magneto ignition.
Two entirely different systems!!
They will NOT work on the Briggs!!


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## Arkie

jhngardner367 said:


> ONAN is a coil/battery ignition,not a magneto ignition.
> Two entirely different systems!!
> *They will NOT work on the Briggs*!!


Right: entirely different systems.

Here is a link showing how you can ******* the Onan system. Note the primary polarity of the second coil is reversed.
http://www.w6rec.com/duane/bmw/points/BMWPointsDiagram.jpg


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## Arkie

Originally Posted by Arkie View Post 
Right. that OEM one is actually marked this side out and the plug wires are too short if mounted upside down. Even on yours it will still mount but the plug wires are too short when mounted upside down.

Most of the generic replacements are not marked this side out and the plug wires are long enough to reach easily if the coil is upside down the waste spark engine won't run with the magneto upside down.

*Also have you ever tried running a waste spark engine with just one coil sparking both spark plugs at same time? (Both spark plug wires tied together so as to fire at same time from a single coil) *
*
that is what the coil I posted does.........................[/B]reading is not one of your strong points



NO  the one you posted is two coils in one epoxy mold, it is not a single secondary coil.

Try taking one of the plugs wires off and insulating it and tieing both spark plugs to the same spark plug wire and see what kind of a run you get. (it's waste spark but two individual triggering devices and coils in one mold) AND one coil is not strong enough to fire both spark plugs at the same time I've seen one side of the Briggs twin magnetos fail and engine only running and sparking on one cylinder and tried using just the one good one to fire both plugs. Try it and see what you get.
I seen a circuit diagram of the internal construction of the Briggs twin L heads magneto some time back showing the two separate solid state triggering of the two secondary coils. *


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## jhngardner367

The OP was concerned with HIS Briggs twin,...not an Onan,...and it's not polite to jack a thread.


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## Arkie

jhngardner367 said:


> The OP was concerned with HIS Briggs twin,...not an Onan,...and it's not polite to jack a thread.



I apologize.

Have a nice memorial weekend.

Bye


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## Ihatemowers

Hi there gents, so I HAD the same issue except I disconnected the kill wire on the coil and it gave me spark, so my question being is that going to end up being the ignition?


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## Ihatemowers

Both safety switches have been bypassed also fyi


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## Arkie

When the wire you disconnected is grounded is what kills the ignition spark. Might trying using a ohmmeter and tracing for the source of the ground. If the unit has a battery disconnect one of the battery posts before you start testing so you won't accidently ruin your ohmmeter due to voltage of accidently crank the engine. With that wire disconnected if the engine starts you will have to apply choke for a kill.

You need to post the name and model of the machine for more precise answers to your question.


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## Xaxor

I realize that this thread is a bit old but I've been having the same problem and came here today for help. I've rebuilt a B&S engine but couldn't get a spark out of the magneto, just like many that posted here. So, what could it be? It's a coil, a moving magnet and high tension lead. Still no spark with or without the ignition (ground) wire. Adjusting the gap did nothing. I thought maybe the wire was broken at the base and took off the magneto to inspect. Then I saw it, embossed into the magneto....."THIS SIDE OUT". Yes, it's possible to install the magneto backwards! After the change, engine started right up....I had the ignition wire still disconnected and the problem was shutting off! Hope this helps.


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## pogobill

Thanks for the information. Welcome to the forum, I was down in your neck of the woods last week.


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## bbirder

Xaxor said:


> I realize that this thread is a bit old but I've been having the same problem and came here today for help. I've rebuilt a B&S engine but couldn't get a spark out of the magneto, just like many that posted here. So, what could it be? It's a coil, a moving magnet and high tension lead. Still no spark with or without the ignition (ground) wire. Adjusting the gap did nothing. I thought maybe the wire was broken at the base and took off the magneto to inspect. Then I saw it, embossed into the magneto....."THIS SIDE OUT". Yes, it's possible to install the magneto backwards! After the change, engine started right up....I had the ignition wire still disconnected and the problem was shutting off! Hope this helps.


Great learning experience. Bet you will never do that again. Sure beats reading it in a book. 
Welcome to the forum.


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