That is unfortunate. If the carb had an internal leak, the fuel that went into the crankcase remains and certainly doesn't help the oil do its job. The reverse is true in fact. The fuel part that is in the oil if small will vent itself out first, but there is the thinning of the oil which is reducing the oils effectiveness. There could be oil loss / pressure building from a head gasket failure- but it goes back to how long this engine has been running w/ fuel in the crankcase and what the correct repair really is. If were talking a couple on 10 minute periods of use nbd, but running long periods of time- you want to push for engine replacement. you will also want to know that there is no debris in the tank that caused the whole thing in the first place.

You have evidently gotten the timing gear out of time! Easy to do when reassembling after opening the case. I use a piece of masking tape, or heavy thick wheel-bearing grease to hold the cam in place, then carefully lower the sump into position!

The most common causes for this are a float that is saturated or not set level / a leaking inlet valve or seat defect. When you install the inlet needle, you may note that some have the little retaining wire that seems to direct itself out a tad sideways. If that is the case- install it away from the housing to prevent binding. If this has a fuel tank under the hood, it is also possible for the fuel to come in through a defect or mis-assembled pump as well.

Suggested troublshooting not yet fully completed, but here's some updates. With the new knowledge that I CAN swap the left/right plug wires, I did. Exact same problems I had before, but as you probably know, exactly reversed. Which means: The cyl/engine is still basically 'good' (humor me there, I like the mower!) - it WILL run on both cyls, just not at the same time. Doh! I swapped the wires back, and the original non-firing cyl was back where it was previously. Glad to know I'm not crazy. I pulled the plug from the good side, grounded it against the block and hit the starter after turning out all the lights but one in the corner. Good looking spark! I replaced the plug/wire, and pulled the other side to try the same thing. This time, I used a pair of insulated pliers to hold the plug against the block. I had a flashback of working my my stepdad's garage when I was 11. The wife and the new baby were VERY happy to hear less cursing this time, but I still cursed a little - because it appeared to have similar spark to the other side. Did both sides again, making the wife watch and she agreed, appeared to be similar spark. I checked all the wiring, no obvious chew marks/rips/tears/breaks. Amazing how well it's held up over the years, why cant my cars do that? Oh yeah, they get used more than once or twice per week. I do have this odd little tool that everyone I mention to thinks I'm crazy - something my father-in-law gave me to check for bad wires on a car. Looks liek the top half of a clicky ballpoint pen - you rub it up and down the wire while the vehicle is running - if it lights, you have a crack/etc. It didnt light at all on either wire - even though I now new both are getting spark. And appearantly gas. so - what the heck?? I came home during lunch today and threw the battery charger on at 2amps for about 6 hours, if anything it has a slightly over-charged battery (charger came off an hour before my testing) So - spark appears good. Must be getting gas or wouldnt run at all on that side regardless of wire. Plugs are good for same reason (but I did switch them and clean them again.) So, the coil has two leads coming out of it - do they both get the magic spark of life from the same place, or does it have two sets of internals, and one side is going bad? I can find 100 sets of instructions on how to test coils but appearantly the wife's rabbit DID eat the leads to my multimeter - so other than the wire to the tongue test, I guess I'm done for the night (note - rabbit was never in the same room as the mower - ever.. I know they love to eat wiring and the 3rd time it ate a computer cord belonging to said Wife, she agreed that bunny is perma-banned from the garage and basement under penalty of stew.)