Help! Lawn mower running on 1 cylinder

Help!

I have a Husqvarna yard tractor/mower with a 22HP twin Briggs & Stratton. Nothing special, it gets the job done. For a while now it has been bogging down when I engage the PTO clutch to run the blades. I can mow the lawn - slowly - but it's a PITA. It seems to be a consistent lack of spark in the left hand cylinder; it keeps running when I unplug that particular spark plug lead with no change in engine note, but cuts out when I disconnect the other lead. I am baffled where the fault might be.

I have swapped spark plugs - both work in the side that has spark. I have swapped coils and tried a new spare - again, both existing coils and the new one work in the side that has spark. I wired the power to the coil across from the good side across to the bad side, and it won't start. I wired both coils from the good side power supply simultaneously, and it won't start. I re-wired the good side coil from the good side power supply, and it starts right up. I can start the engine when it is entirely disconnected from the main mower electrical system, so it must be getting current from the regulator - in this case I cannot switch it off with the key, and have to pull the spark plug lead. It is a new regulator I got off a junk mower with a newer version of this engine engine, but I wouldn't expect this would be an issue?

I am totally stumped. Can one of you with a few more brains than I suggest things to check? Schematics below; link to a downloadable copy if the picture below fails.

Appreciate any help in advance.

Electrical schematic

So the prob is when the PTO is engaged, your missing on 1 cyl?

id disable the kill wire and see what it does. 

Also, maybe check the carb. Some of the low 20hp briggs had 2 barrel carbs so 1 sides jet may be clogged. 

Nope, runs on 1 cyl all the time.

The non-firing side plug gets wet - would that be from fuel or (in the case the jets are blocked) oil vapour?

compression check?

Compression was my thought as well.  I had one the the valve spring seat became dislodged and kept the spring from closing.

Is it a single cylinder?

Haha!  

Dumb question...  did you actually check for spark on the non firing side?

Sounds like you are already finding some faults past that point, but it wouldn't hurt and is stupid easy.

Sounds like a spark issue due to some wiring fault.

cdowd said:

Compression was my thought as well.  I had one the the valve spring seat became dislodged and kept the spring from closing.

Since the plug is wet, it seems like the intake is is at least opening, or or possibly stuck open. 

I’d wait on the compression check (beyond a thumb over the plug hole while turning by hand) and start by taking out the 4 bolts to pull the valve cover. 

Check the valve clearance and adjust them so you know the valve is able to contact the seat. They may have worn enough to not be fully closing.

B&S V-twin...pretty common for the valve spec to run out of adjustment over time and the pushrod will come loose, thus not activating a valve. I just took in a tractor with that exact problem. Reset the pushrod, adjusted clearances and it runs like a champ. Pop off the valve cover on the offending side and see if it's still under the rocker arm.

Don't those motors also have the weird low rpm compression release system for starting that routinely fails? I would start with a valve adjustment and go from there. 

Thanks y'all - will check that out. For a short time it was making a weird noise as if the ignition on that side was making it's way into the exhaust, as it was way louder on that side. So perhaps it's something related. Is a pushrod adjustment easy to do?

Just a feeler gauge, wrench and either hex key or screwdriver (I forget which one mine had). 

Loosen the jam nut, adjust the clearance, then tighten the jam nut.

Toughest part is finding the specs, but I’m guessing someone on here will know  

Im 99% sure it has a compression release.  If i remember right, you have to set the valves right off TDC. If you set it on tdc it might make the compression release not work and it will have a hard time cranking. Not positive about that but ive read of it before. 

I can't hear the name Husqvarna without thinking about fear & loathing 

ddavidv said:

B&S V-twin...pretty common for the valve spec to run out of adjustment over time and the pushrod will come loose, thus not activating a valve. I just took in a tractor with that exact problem. Reset the pushrod, adjusted clearances and it runs like a champ. Pop off the valve cover on the offending side and see if it's still under the rocker arm.

Yes, the B&S V-twins are notorious for this.  It's especially likely if it has gotten too hot, often from a blockage in the cooling airways.  (In my case, it was a mouse nest)

Also, in my case, the pushrod dropped out and fell into the crankcase.  In order to retrieve it from the crankcase, the engine case will have to be split...by someone else, if it is ever to get done  

Just pull the valve cover off of the offending cylinder.  If what has been described has happened, it will be immediately obvious.

That doesn't look right:

So it appears BOTH pushrods have come out of adjustment and fallen out. One of them is snapped - you can see the fractured end, and the other 1.5 pushrods worth of pieces are nowhere to be seen. I assume they are sitting (hopefully innocuously) does the bottom of the crank-case, where they'll never (again, hopefully) get snagged in any fast-moving mechanical bits.

I think I'll order 2 sets and replace both sides, as I don't imagine the rods on the functioning cylinder would necessarily be much better.

How does one measure the clearance between the domed top of the rod and the receiving rocker-arm-end? I have a feeler gauge, but if the rocker arm is concave, how do you measure accurately?

Measure the clearance at the rocker to the valve stem.

I love it when I'm right. It happens occasionally but my wife doesn't believe it.