b & s model 126612 used in small 2kw generator. have been trying on and off for months to be able to start this thing. total running time is about 3 hours so the engine is practically new. fuel has been drained each winter. after almost losing my arm a few times due to snap backs , i let it go. it did start a few times over the years and then continued running with no problems until i shut it off.
everything is there, fuel, good spark and timing etc. all seem to indicate that the pressure release mechanism was not working (easy start), so i pulled the head to check it out. the inside of the head was covered in oil. doesn't smell as though gas was mixed with it. after cleaning the oil away and running the piston up and down, there is a smear of oil on the cylinder wall. the pressure release seems to be working since the exhaust valve opens slightly about 3/4 the way up on compression and then closes tightly together with the intake valve. no scoring of the cylinder wall, slight blackening of both valves. the head had a build up of black greasy soot which could be removed with a rag. as i said, this is practically a new motor so cant believe that the rings are shot on the piston. so... whats cookin?... thanks.

You never know. It could be a lemon.

some more info regarding the model. its a quantum 4.5/5 hp (L head) vertical shaft with a speed governor (generator is connected on the bottom like a lawnmower). starter is a pull rope and pulls clean when no spark plug inserted when the head is on. automatic choke with no primer button. when it is transported there is a tilt of about 25 degrees with the front of the head tilted backwards. never been laid on its side which would cause this condition.

you should be able to tip it , as long as you tip toward the exhaust side , could be the crank case breather , did it smoke like a house on fire when it ran ? could be an inertia thing , are you getting a good pull on it ? is the rope long enough ? would a bigger handle on the pull rope help . as far as the crank case breather goes you could pull off the tube and see if it has any oil in it , could have a loose bolt through the armature , flywheel key could be partially sheared ,

thanks for the reply from all. i found the problem by being a bit more accurate in my investigation. without joining the forum, i probably would have just put the thing in the corner and left it. In examining the cylinder bore previously, I used a plain flashlight and noted that everything looked smooth. running my finger around also indicated no problem. BUT now, doing a fingernail test detected a distinct groove up one side (only one).. on that side at the top of the piston there is a small carbon deposit and the only deposits on the top of the block where the head bolts to are above the groove area. I did not take note of this before since I expected some carbon traces but now it all falls in place. This is where I get my oil in the cylinder. with everything mounted, the oil evidently blocked the valves and faked the indication that the compression was good and there was nothing wrong with the piston or cylinder wall. (real tough to pull the starter rope with the plug in and ok with it out). the groove and deposits are on the exhaust valve side of the motor so I guess it heat did the job one way or another. Into the junkbox! :(

if you are talking about the ridge @ the top of the bore its kinda normal