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I’ll try and keep this short

Rebuilt motor last year in spring. Ran great this spring. Pulled out of mower and had mouse nest in flywheel area. Used mower for a 45mins. Ran a hair rough but still ran, just slightly off. After 45 mins it started running quite rough then died. Started up then died. After twice it won’t start at all

cleaned plugs and fired right up then immediately dies. Cleaned plugs and fouled again-gas fouled
Took plug off wire... fires up and runs good if I send spark from open wire to plug.... soon as I connect plug or move to far it dies. This is same on both plugs. I installed new coil last year
Choke doesn’t seem to play a part in running and throttle doesn’t seem to play a part. I rebuilt carb a few years ago

im leaning towards some mouse gunk on top of case/under flywheel/around coil but would like to hear some options before I take the time to undue everything again. I’m open to ideas

thanks in advance

Check the kill wire to the coil for chewed through insulation that is shorting out against the engine.
The kill wire should be open ( neither power nor ground ) and goes to ground to stop the sparks
So if the insulation is breached and the bare wire can touch the engine, no spark.
Double ended coils have a + spark at one end and a - spark at the other and if the insulation is compromised anywhere you will get bad / no sparking

Clean the mouse crap off the engine... check to be sure fluffy didnt chew threw the coil kill wire letting it ground out the coil producing no spark

Xbenx927 said:

Took plug off wire... fires up and runs good if I send spark from open wire to plug.... soon as I connect plug or move to far it dies. This is same on both plugs. I installed new coil last year
Choke doesn’t seem to play a part in running and throttle doesn’t seem to play a part. I rebuilt carb a few years ago

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Going back to my school shop days, back when cars had carbs and could be tuned (!!!). If I recall correctly, pulling the plug wire off a bit from the plug is equivalent to retarding the spark, something you have to do if the mixture is too rich. The clue is in your first post - gas fouled. I'd check the float or choke control again before tearing the engine apart.

Pulling the plug wire away slightly doesn't retard the timing (speed of light thing) It acts as a booster gap and increases the amount of energy it takes to junp both gaps. Back in the day of cars with point ignitions one of the snake oil products in the JC Whitney catalog was the Spark Intensfier that made the car run better with fouled plugs. It was just a booster gap you plugged into the distributor cap. Works great till you try to start the car on a day below freezing and the battery is a little low and the ignition system doesn't have the energy to jump both gaps. Your plugs are probably fouled and the ignition system is fine. Figure out why the plugs are fouling, oil or gas then install NEW plugs.

Hammermechanicman said:

Pulling the plug wire away slightly doesn't retard the timing (speed of light thing) It acts as a booster gap and increases the amount of energy it takes to junp both gaps. Back in the day of cars with point ignitions one of the snake oil products in the JC Whitney catalog was the Spark Intensfier that made the car run better with fouled plugs. It was just a booster gap you plugged into the distributor cap. Works great till you try to start the car on a day below freezing and the battery is a little low and the ignition system doesn't have the energy to jump both gaps. Your plugs are probably fouled and the ignition system is fine. Figure out why the plugs are fouling, oil or gas then install NEW plugs.

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Thank you for refreshing some worn out brain cells! JC Whitney. Wow. That's a name I've not heard in decades. Used to pour over that catalog. Plastic VW body parts! Cheap AM radios also. Custom fit? Nah, just use a couple of L brackets under the metal dash...

Thanx guys for all the responses.
I figured either mice chewed something or part of their nest got wrapped around and did some damage. I just couldn’t put my finger on it to pull the trigger on tearing into it more. I was looking for some reassurance and sounds like most are on the same page. I’m sure it will be an “ah ha” moment when I get in there

I’ll let you guys know what I find. Thanx again everyone!

I thought about this as well but being I had no issue lately and it was acting weird I figure odds are it’s something new (something caused this) before I go searching in a random area. If the mouse nest wasn’t there I would likely start at the carb since that’s logical with having spark. If I had not tested spark the way I did and didn’t see the nest it could be a wild hunt. Amazing how fast those little buggers set up shop. Gone for 2 months and I’ve killed 15 in 4 days in the shed. Shed looks like a anti mouse military base now lol

wrldtvlr said:

Going back to my school shop days, back when cars had carbs and could be tuned (!!!). If I recall correctly, pulling the plug wire off a bit from the plug is equivalent to retarding the spark, something you have to do if the mixture is too rich. The clue is in your first post - gas fouled. I'd check the float or choke control again before tearing the engine apart.

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Barn cat time!

Hammermechanicman said:

Pulling the plug wire away slightly doesn't retard the timing (speed of light thing) It acts as a booster gap and increases the amount of energy it takes to junp both gaps. Back in the day of cars with point ignitions one of the snake oil products in the JC Whitney catalog was the Spark Intensfier that made the car run better with fouled plugs. It was just a booster gap you plugged into the distributor cap. Works great till you try to start the car on a day below freezing and the battery is a little low and the ignition system doesn't have the energy to jump both gaps. Your plugs are probably fouled and the ignition system is fine. Figure out why the plugs are fouling, oil or gas then install NEW plugs.

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Actually Hammer you are not quite correct.
Increasing the gap does retard the spark.
The potential between the electrodes does not go from 0V to 30,000V instantly but rather starts at 0V then rised to 30,000V then drops back to 0V again in a sine wave form.
Now the time is very very short, but it is a typical wave.
The rest is correct, the spark intensifiers ( which have been around for 100 years ) just put a resistance before the spark plug that is greater than the resistance of the air gap of the plug so the rise from 0V to 25,000V happens at the intensifier and the first potential the plug sees is the 25,000V which was often enough to make a fouled plug spark rather than track down the fouled electrode.
The std fix for a fouled plug was to pull the cap on a running engine about 1/4" to 1/2" off the plug and hold it there till the cylinder started to work with the cap on properly.

The "advance" on a lot of EI chips is just that, a bank of resistors that go in & out of circuit in order to reduce the amount of retardation of the spark as you can not advance it electronically.
The old Atom Industries EI chips did exactly that.
The different chips had different internal resistance to change the amount of retarding of the trigger signal.

Xbenx927 said:

Amazing how fast those little buggers set up shop. Gone for 2 months and I’ve killed 15 in 4 days in the shed. Shed looks like a anti mouse military base now lol

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It's a bit of thread drift, but you struck a chord. I've been channeling my inner Bill Murray Caddyshack these past few weeks. Have multiple colonies of the little blighters creating large mounds of dirt in the back 40. Makes mowing a pain and looks like crap. Started with bait stations, graduated to dropping the bait down the entrance hole. Unfortunately, they've started to wise up as each morning I find they've pushed some of the bait back out of the tunnels. Still, I must be making some progress as they are having to dig new tunnels. Spouse wants to know what the modeling clay rodents are in the garage.

wrldtvlr said:

It's a bit of thread drift, but you struck a chord. I've been channeling my inner Bill Murray Caddyshack these past few weeks. Have multiple colonies of the little blighters creating large mounds of dirt in the back 40. Makes mowing a pain and looks like crap. Started with bait stations, graduated to dropping the bait down the entrance hole. Unfortunately, they've started to wise up as each morning I find they've pushed some of the bait back out of the tunnels. Still, I must be making some progress as they are having to dig new tunnels. Spouse wants to know what the modeling clay rodents are in the garage.

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You haven't had to clean out a pool yet, have you?

People originally domesticated cats to control rats & mice.
SO yes get a cat, lock it in the shed overnight and only feed it in the morning.
OR
get a couple of carpet pythons, same story, leave them in the shed and make a nice sunny place for them to lay & digest your problem.
A big one can knock off a dozen or so mice in a single night but of course will not hunt for another week after that.
Snakes have a double effect because they leave a scent trail that mice will not cross unless in a frienzied plage

Field mice are hard to control as they will not take most house mouse baits and are too light to trip most mouse traps.

Take away the food source and the mice and moles go away. Spray the yard for bugs/grubs. Leave nothing for them to eat or shelter in.

Now back to the original problem. Gas fouled plugs means needle and seat to me. Float level setting should be checked. Flip the carb over with the bowl off. Raise and lower the fuel float with your finger. Blow into the fuel inlet pipe. You should be above to control your exhaled breath with the plastic float. Just like a toilet works to fill the tank up.

slomo

Our place is 30 mins outside of town on a river in the middle of the woods and the closest neighbor is a few hundred yards away. I was actually joking about a barn cat yesterday before this post. We are by the river and have an Indiana Jones type feel on the river bank which is 5’ from rivers bank edge. Also a lot of coyotes and bobcats. Put the dead ones around the shed as a warning lol. Seen coyote prints and they are all gone over night... we had a bobcat in the spring on our porch 2’ away from glass door wall in the front 3 different days....pretty cool to watch nature that close. Oh and we have a lot of bears but I don’t see them catching mice. I love the snake idea and very surprised I’ve never had one in the shed. I’ll be digging into this later today and report back. I’ll start with checking above crankcase and looking at coil and wires, I’ll have to clean that all out anyways. If that all looks great I’ll migrate to the carb and check that right quick. I’m not a guru on all of this but I have good understand and have taken everything apart at one time or another.
Side note.... I understand some would look at carb first but that doesn’t quite add up if it was running for 45mins then decided to fail. If motor runs great when plugs are essentially boosted then when connected dies that does sound like a kill wire when reconnected it grounds it out. Although that could be hidden by being boosted but seems like the first logical area to check
Talk to you guys in a few.... great group of guys on this forum and lots of great minds
Thanx guys!

Well. Let the games begin. Took top covers off. Cleaned mouse area. Apparently that was on opposite side of coil. Checked wires from coil. Took coil off and cleaned contacts. Checked kill wire and kill connector. Drained bowl and checked throttle,choke, governor springs and made sure no bad springs or binding.

think I’ll check ignition and clean that contact. It’s looking like it’s time to dig into carb unless someone could tell me how to test coil. When I get done with carb if still doesn’t work only other thing I can think of is bad coil. Just weird it will work when boosted and not at all when connected

Which ignition system does this twin use?
according to my opposed twin manual, newer ones used Magnetron coils, and older ones used points and condenser.

Scrubcadet10 said:

Which ignition system does this twin use?
according to my opposed twin manual, newer ones used Magnetron coils, and older ones used points and condenser.

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not has a coil w 2 wires and kill wire. On back side of flywheel/plate is a magneto. It’s round. I think I have the bigger of them or second biggest for my model. On the big plate is a magnet facing out or possibly 2. It charges from magneto.
I’ve rebuilt the carb before. I pulled it apart and checked ports, needle, float. Float was a hair loose so I bent tan a hair. Needle n seat looks great. Tested plugs out of motor not against metal and against metal and light to no spark. Going to get new plugs to throw in. Idk where spare set is
on good not I didn’t see plugs fouled with gas so.... put new plugs in and test again. Also disconnected kill wire and tried connected n unconnected with no firing of motor. Just wanted to see if that would isolate a section of wire or grounding. Let ya know in a few

I’m not confident it’s fixed but everything is functioning as of now. Here’s what I did

put new plugs in. Still no start. Checked plugs and now weren’t fuel fouled so went to carb. Checked bowl and nothing inside. Looked at fuel pump real quick, looked good, Took float out and adjusted float/needle tab and reinstalled.Tried to fire again and fired right up. Blew a bunch of carbon and cleaned right out but that makes sense considering.Revs all the way up. Isles all the way down. Sounds good. Dialed in needle a hair then let run for a few. Drove around for a min and shut her down. Waited A few and fired right up again. So I honestly don’t know if I fixed anything. Possible loose kill wire towards ignition or possibly something in float needle port that unlodged. I just don’t understand it fouling with slightly stuck open needle and not running on full throttle ?‍ If anything the float was a bit loose from pressing on needle

we’ll see in time