B&S - ran for 1/2 lawn, now backfires

[bxd20]

I pulled out the old push mower - B&S powered. Admitedly, it is very old, but only used about 2 hours a year over 4-5 mowings. It took a few more pulls than usual, but did start on its own (no 'tricks' like starting fluid, etc).

I mowed 1/2 the lawn (20 min) and shut it down to do something else. Came back, can't get it to start. Tried starting fluid, no help. It doesn't sound like it's even trying to start, other than 1-2 backfires, pops, per pull. I replaced the air filter, spark plug, confirmed spark, etc. Spark is good, so the fundamentals of an engine tell me there is a fuel problem. But the starting fluid into the air intake didn't help..... setting throttle very low doesn't help.... setting throttle at full speed doesn't help. Just a subtle "pop" backfire and nothing. So if spark and fuel are good, what am I looking at? Can it be I have a stuck valve? Engine was not run low on oil.

Thanks!
Brian

 

[bxd20]

Let me clarify, I am quite sure it's 'backfiring' through the carb, not the muffler. So - I should suspect intake valve? Remove plug and squirt WD-40 in there and pull the rope a few times? Try to move valve through the plug hole? Use motor oil in the plug hole? I've read a lot of these suggestions.

 

[EngineMan]

You have spark and you have fuel......but do you have compression..?, do a compression test to see.

 

[Rokon]

Let me clarify, I am quite sure it's 'backfiring' through the carb, not the muffler. So - I should suspect intake valve? Remove plug and squirt WD-40 in there and pull the rope a few times? Try to move valve through the plug hole? Use motor oil in the plug hole? I've read a lot of these suggestions.

Sounds like like a timing issue. Check the flywheel key. 6.5 BS vertical engine?

 

[Rivets]

Doubt it is a timing issue. I suspect a compression problem, like the intake valve sticking when it gets hot.