Sounds to me like it blew out one of the crankshaft seals which prevents it from 'supercharging' the fuel/air mix into the cylinder (worse than a bad reed valve because it also reduces the intake charge). On a LB that old, the original seals will be hardened and cracked. Fortunately it's easy to do on all engines prior to the 'E' (Duraforce). You must remove the air shroud and flywheel for the upper one and the blade, adapter, muffler and muffler plate for the lower - may be best to just take the engine off the mower. Polish the lower crankshaft with crocus cloth to remove rust before removing old seal or installing new. Use ordinary seal picks and driver from the auto parts. You can make a driver out of plastic plumbing pipe just big enough to slip over the crankshaft. Clean and oil crank before installing seal.

Yes I have done that several times. There was no gunk in it at all but I did clean the 2 holes near the threads and the one on the top with a fine wire. Any other suggestions? Another thing to note, it does not start when I use the priming bulb however I can see gas coming up out of the spout. It only works if I spray carb cleaner deeper inside. This post was edited by cmilot6329 on Wed, Aug 6, 14 at 11:32

My Stihl 028 won't start. It ran fine last month. So far, the following has been tried: 1. I've replaced the coil and plug. There is a strong spark. 2. I sprayed fuel into the carb. 3. I've pulled the kill wire. 4. I checked the flywheel key. It is fine. 5. I tried new fuel. The saw won't even sputter. The piston is moving up and down as it should. I can't figure it out. With spark and fuel, it should do something. Any ideas?

I assume from your description that the tractor is running well, and the blades cut off with no warning and needs to cool to restart? Covering the basics would be to ensure good grounds and sound harnesses, determining that the clutch is adjusted correctly and the deck is working freely. Maybe a convenience relay? Some have 2. The 917 # would be helpful.