Well there's a couple of things that come to mind. I'd say first check the oil for gasoline in it, this could happen if you have some washed piston rings. This happened to me, some gasoline got into the cylinder while replacing the injector causing it to dissolve the oil that sealed the piston/rings and cylinder wall. If this happens your oil will be really really thin and smell like gas. This could also cause the gas/oil mixture to be pushed back up into the chamber where the plugs are.
If that is the condition you need to drain the oil and you might be able to re seat/seal the piston rings by putting a little transmission fluid or just oil down the spark plug hole, not too much though. I the cylinder is flooded w/ gas or the gas oil mix, you'll have to empty that first before putting anything other fluid in there. I removed the gas from my cylinders via a long spray bottle top. You might have to repeat the re seating/sealing a couple of times. Then refill your oil and there you go. Don't be surprised if you have another injector problem, I've had 3 blown o-rings before I got it right.
All this assuming that nothing is majorly blown, if it is, i forsee a rebuilt
What I went though, might help IMO,
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Good luck.