no spark after replacing magneto and spark plug

[Mocontrolsguy]

Hello all and Happy Memorial Weekend!
I have been trying to restore/repair a swisher pull behind mower. It has a Briggs and Stratton 11.5HP vertical shaft engine. The guy I purchased it from said he had problems with the spark, but he believed it was in the kill switch section. I started by downloading the manuals and finding the replacement parts for the magneto, spark plug and a few items for the fuel system. the first thing i checked was the resistance of the old magneto. Measured a little over 20K Ohms, and the kill switch measured 0.1 ohms. I pulled the magneto out, gapped it to about 0.010 (ten thousandths) then put in the spark plug. I started with the repair guys' recommendation of the Champion 71-1 (read 10K ohms resistance) but I ended up grabbing every stinking spark plug I had in the shed to find something that would work. I checked the magneto after installation, it reads 10K ohms, to me a bit high, but still within specifications. the kill switch wire is not connected to eliminate that area of troubleshooting. I clamped the spark plug to the side of the engine block where I could watch for a spark. there was none, not even a faint yellow glow. Doubting the spark plug was fully seated in the connector, I measured the resistance, and it came to 15K with measuring at the center electrode. I am at my end of the pull rope. Any ideas?

 

[Scrubcadet10]

Could you provide the model number of the Engine please?
Do you have the coil on correct? It usually marked "Cylinder side" to face down, I would also try cleaning the mounting posts the coil mounts to with sandpaper.
You could also put a bit of gasoline in the plug hole, install the plug and wire, and try to start it. That should tell you.

 

[logert gogert]

I would also try cleaning the mounting posts the coil mounts to with sandpaper.

Yes, please do that, often times people have the same case as you did, and i also had the same case, but the coil and magnet were a bit rusty, a little bit of sand paper, and thats all it took.

 

[Mocontrolsguy]

Could you provide the model number of the Engine please?
Do you have the coil on correct? It usually marked "Cylinder side" to face down, I would also try cleaning the mounting posts the coil mounts to with sandpaper.
You could also put a bit of gasoline in the plug hole, install the plug and wire, and try to start it. That should tell you.

thanks for your help!
Sorry, I forgot to include the engine number.
217802-0145-B1 and the manufacture date is feb 2009. Coil is a 595304, the clerk said this was the replacement coil. I put a wire brush on my drill and buffed the mounting posts because it did have some corrosion on it. The coil had the Cylinder side marked, so I put it face down. I also brushed the flywheel to see mainly if the magnet was in place. It was, but I wasn't impressed with its strength. it would hold a screwdriver by the shaft, but just barely.
I will pour a bit of gas in the hole and give it a shot; since the mower has been sitting for a couple of years and i saw water in the carb when I was tugging on the rope, I wanted to see if I could get the fire going first.

 

[Rivets]

Couple of things you should know about your engine before you continue to throw money at it. First you cannot properly measure resistance on today’s coils, due to the triggering mechanism in the coils. Second Logert, rust has no effect on the magnetic flux, so sanding the coil poles and magnets is only cosmetic. Loss of magnetic strength is extremely rare. Third, if you see water in the carb you must solve that problem first. Even a small amount sitting in the carb will change fuel ratio greatly. My suggestion is to get all water out of the system by draining the tank and carb float bowl. Second, check for spark with the kill switch wire removed. Third, Install a new plug, Champion RC12YC, in to the engine. Fourth, if you have spark, dump a little fuel into the carb throat and see if it will fire. If no luck check your valve clearances. Let us know what you find. Forgot to say at the start, check to see if your oil level is right.

 

[tom3]

Check for flywheel magnet, hold/hang a long screwdriver about 3/4 inch away from the magnet, should pull the screwdriver in pretty solidly.

 

[Fish]

If you have an electric starter with a battery, and trouble with the keyswitch {like wrong one}, you could have destroyed the new coil. If voltage is sent to the coil through the kill wire, it will kill a coil, even a new one.

 

[Grousemansav]

Hi Rivets. I'm confused about testing the magneto. If you go to this you tube video it shows how to test the coil (

). The fellow really seems to know what he is talking about. I just tested my coil and got 0 ohms from the base to the kill wire (ie shorted to ground). So I figure my coil is bad.

Grouseman

 

[bertsmobile1]

Modern coils are NOT repairable thus testing them by any means other than on the engine , kill wire removed is a waste of time .
You can test the spark plug wire but again on most coils it is not replaceable either .
Depending upon how the Hall Effect trigger is wired, some can be tested with an Ohmmeter and some can not be tested with an ohm meter.
Ohm meters work by sending a VOLTAGE down the probes and measuring the drop in voltage caused by what ever you are testing.
Some Hall effect chips are very very voltage sensitive and if the voltage applied by the ohm meter is above what the chip is above what the chip is designed to tollerate then the chip gets fried .
Thus the very act of measuring the resistance can fry the chip, particularly if you are using a cheap Ohm meter.
The ones the factory recommend are several hundred dollars, not a Harbour Freight give away.

Now the presented has a nice authorative voice, but all he has done is to make a video f what is written in the service manual and to be fair at the start he did add the disclaimer that what he was doing is only correct for the particular engine.

BEcause coils are not servicable and because cheap gear can destroy a perfectly good coil most engine makes do not publish any test data
In this case , the chip is a complicated one where the chip grounds the coil when there is no voltage, then opens the coil so it can saturate then closes it again so it can discharge & generate a spark.
Most are normally open so you get an open circuit reading when you try to test them with a meter between the kill wire and anything.

So if you got no spark with the kill wire off when you cranked the engine then the coil is bad
If you got a poor with the kill wire off when you cranked the engine, or no spark with a plug connected but a good spark when grounded then your plug cap is suspect.
However now days, the plug wire is so short there is not enough length to replace the cap if it is bad.
On Briggs coils you can fit a screw on Honda style cap as there is 1/2 " of connector inside the cap to make up for the bad bit you cut off the end oof the spark plug wire.