Craftsman tractor issue - out of ideas
This is my first post, as I'm now completely stumped as to why my Sears lawn tractor won't start.
6+ year old Sears 917.273404 tractor with B&S engine 31P777,
Last year we gave the electrics a full overhaul (cleaned all corrosion, new battery, electrical grease on contact points). It also had oil change. It is stored with no gas in the tank (run dry) over the winter and battery pulled out.
This spring it had oil change, and mower platform was dropped off for cleaning and lube and replacement of safety spring to auto-disengage blades.
We always run 91 octane gas in it with a little "stabil" for good measure.
We were mid-season with it this year and it had been running well then it started sputtering. so turned off and filled up with gas (very low). After that it will not start.
Engine turns over (may too easy) but won't run.
First few tries some back fires and flame in the air intake. After that nothing.
What I've tried:
1) I drained the gas and verified fuel filter was not clogged.
- I put freshly bought 91 octane in the tank.
3) sprayed a little carb cleaner into the air intake while turning over = back fires and flames in the air intake.
4) pulled the spark plug and turned over the engine = good spark.
5) *bought and installed* a brand new *fully assembled carb* ($80) from sears parts (including fuel cut off solenoid).
6) installed new air filter
7) Verified diode on alternator is working with multi-meter on diode test.
8) ** Attached electrical plug to new fuel solenoid in both orientations (not keyed). - I'm guess polarity doesn't matter ?
Verified 0V to fuel solenoid when ignition off, 12V when on , ~9V when cranking.
9) Used a 3M engine cleaner kit chemical with hose past the (old) carb to spray carbon cleaner into the engine.
** with spark plug removed put finger of plug hole and turned engine over - finger was NOT pushed off, slight vacuum actually. (??)
I look forward to suggestions - time to look at the valves?