Briggs popping until it stops

[puttinalong]

Hello all, I am an old user from the previous forum "PERR" and I have been away for a while but I am finally getting more time to work on stuff again and I need a little help. I am working on a Briggs and Stratton 13HP (28T707/1154-E1/010410ZD). I found out that the owner will complain of cutting grass and it would stop on every round of grass but would restart for another lap. I got it and cleaned junk out of the fuel lines, cleaned carb since I was there, and put a new spark plug on it since it was the original from 2001. I pulled the head and the valves didn't look that bad to me but that is the only thing I can think it could be. I started it and ran it and the longer it runs, the more it pops and the engine hunts up and down. The longer it runs the more it runs erratically and then it runs till it cuts off. Does this sound like a leaking valve seat? I am hoping to lap the valves tomorrow but I wanted some input if I could get some. Thank you.

[RoyM]

That sounds like a fuel starvation issue. Does it have a pump and remote tank? Check the pump impulse line for cracks.

[bobodu]

Did you check the valve lash??

[puttinalong]

I haven't checked the valve lash yet...no excuse for it especially since I had the carb off of it and a clear path to the breather. I did observe the valves closed and tried to spray lubricant around the seats to observe if any would seep past but I didn't observe any lubricant that had made it past the seats. I will check the valve lash, when I can get some time. I just didn't know if I was in the right area.

---as for the post before bodo---I had cleaned the carb and it appeared clean as a bean, nothing unusual in the bowl, no signs of ethanol acid damage...but at this point I guess it could be anything.

[StarTech]

Don't forget to check the fuel tank vent which can cause lack of fuel flow if partially plugged. Most are in the fuel cap. Try leaving it loose and see if the problem goes away.

[puttinalong]

Yessir, the tank vent was checked already and it is fine. I already learned my lesson on that one before, like chasing a ghost only to have it staring me in the face every time I looked under the hood. Could have been a snake and bit me 10X over.

[StarTech]

You just had to mention snakes didn't you? Just a had a mower brought in this week with a 3 foot garter snake in the operator station. Really woke me up to say the least . At least it was non-poisonous snake.

Customers are bringing in a lot of worn out engines so far this year and some of the mowers look like they have sitting outdoors unused for years.

Keeps us posted on the outcome. I haven't seen one doing this yet but it will be my luck one will come in soon.

[puttinalong]

UPDATE: Checked valve lash and that is on the money. I don't have (but will soon get) a set up to pressure test. The only thing I can think is the valves may possibly need to be re-lapped. I am going to attempt that today. I pulled the valves and the face on the exhaust valve appears a little thinner than I think it should be so I will see if that does it. If that doesn't work, I am going to throw my hands up and take it back to my friend with a big 'ol "I don't know" and suggest they get it serviced more than once every 8 YEARS to avoid something like this in the future.

[mwerles]

Check the wiring to the kill switch,may be intermittently shorting to ground, popping sound would be from ignition being interupted and then working again,then igniting excess fuel.
Les

[38racing]

Is it new enough to have an anti backfire solenoid on the carb