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riharley · 05-26-2011, 01:08 PM

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

**dangeroustoys56** · 05-26-2011, 03:21 PM

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).

riharley · 05-26-2011, 04:14 PM

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?

riharley · 05-26-2011, 04:42 PM

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?

**jhngardner367** · 05-26-2011, 04:46 PM

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 .

riharley · 05-26-2011, 04:52 PM

what should the gap be?

**jhngardner367** · 05-26-2011, 04:53 PM

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!

**jhngardner367** · 05-26-2011, 05:04 PM

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.

riharley · 05-26-2011, 05:57 PM

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

**dangeroustoys56** · 05-26-2011, 07:10 PM

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.

riharley · 05-26-2011, 08:06 PM

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.....

riharley · 05-29-2011, 09:10 AM

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

Mickey · 05-29-2011, 10:27 AM

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?

riharley · 05-30-2011, 07:50 PM

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?

**jhngardner367** · 05-31-2011, 12:11 AM

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

riharley · 05-31-2011, 10:25 AM

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?

Mickey · 06-01-2011, 10:31 AM

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.