Briggs & Stratten 20HP won't start, backfiring through exhaust and carb.

Novo

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  • / Briggs & Stratten 20HP won't start, backfiring through exhaust and carb.
Hello All.
Kinda Quick "complete" back story :),
This is a 8yr old Ariens 46" riding mower with Briggs 331777-2372-G5 20HP OHV INTEK single cylinder engine. Given to me after it quit running.
I suspected it had a broken rod and pulled the engine. The rod/cap was broken and no other damage to case "except" the sump cover's bearing surface for crank shaft was scored from debris.
I Cleaned the housing of old oil and debris, installed new piston, piston rod, rings and ordered new sump cover/gaskets.
When I reassembled, I was careful timing marks "dots" were correctly aligned and governor was resting correctly against tab, then tighten everything to B&S spec's.
I had also pulled the head to install new piston and inspect valves. The valves were fairly clean seated and not bent. After closing the sump cover, replacing head gasket and installing the head; I checked valve clearance and it seemed fine. "made sure correct Aluminum push rod under intake"
I reinstalled completed motor on mower and proceeded to pull the Fly wheel bolt to see if the key-way had sheared and indeed it did! Replaced key-way and reassembled.
Inspected gap on magneto coil and it seemed fine/not moved.
Tried to start it once but backfired and I quit for the day."figured to be back on it in morning"

Next day I went to start and this time it STOPPED rotating at compression stroke. I suspected I may have over looked proper valve adjustment and pulled the valve cover.
"Gasoline" came pouring out of valve area. Drained the engine sump and found all the contents of fuel tank had drain into engine over night. Read a post about this condition and pulled the anti backfire solenoid. I found it was slow to move/sticking. Cleaned the solenoid out and inspected the carburetor visually while still attached to engine. The bowl was very clean and float adjustment seemed fine. Reassembled every thing, rotated engine with new oil, drained and added new oil again.
(wanted anyone reading to have complete rebuild history)

All That to lead to this question: Battery is fully charged, engine turns over as excepted but it backfires from both carburetor and exhaust randomly no matter the throttle setting.
Never starts or runs even a little "although the engine seems to out pace the starter some times" as though it's firing some.
I have checked gas, "no water"
Checked valve clearance again. ."is good"
I checked flywheel key again "it's good"
New spark plug and is getting good arc,
Sprayed starter fluid direct in breather tube "no filter" and still just back fires.
I'm at a loss. Maybe carb needs cleaning, but I thought it would run at-least a little with starter fluid. ALL suggestions or any questions are welcome, please:)
Thanks in advance!
 

dana a

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  • / Briggs & Stratten 20HP won't start, backfiring through exhaust and carb.
IT SOUNDS LIKE THE TIMING IS OFF. If timed right it will run without a carb just by spraying starting fluid in the intake. Possibly either the crank or cam shaft has 2 marks on it
 

Novo

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  • / Briggs & Stratten 20HP won't start, backfiring through exhaust and carb.
Dana,
The "Cam shaft Gear" has ONLY one dot between two teeth so I'm sure that's correct!
However the crank has "best I can tell from through scratches/scaring" a "tiny" dot on one of the teeth and several teeth away, a rectangular indent.
I lined up the dots.
I agree it acts like timing issue and yeah I expected it to at least run for a sec on starter fluid if it were a fuel issue.
If no others have easier check before tomorrow morning, I will pull the engine again.
Haven't seen any definitive pics on my particular engine and the timing marks so I will post pics tomorrow when I get that far.
Thanks for responding!
 

Tinkerer200

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  • / Briggs & Stratten 20HP won't start, backfiring through exhaust and carb.
As a side note of information, the anti-back fire solenoid on the carb has absolutely nothing to do with the possibility of the carb float not sealing and flooding gas thru the carb into crankcase. You did properly torque the flywheel nut/bolt when installing new key?

Walt Conner
 

raider820

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  • / Briggs & Stratten 20HP won't start, backfiring through exhaust and carb.
Take another look at the flywheel key.
 

Fish

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  • / Briggs & Stratten 20HP won't start, backfiring through exhaust and carb.
Sounds like a stuck valve, or loose seat.
 

Novo

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  • / Briggs & Stratten 20HP won't start, backfiring through exhaust and carb.
Sorry to all that replied for my late reply! I'm in Texas and the rain has prevented me from doing any thing to the mower yet.

"Fish" I had the head off and checked the valves for sticking or bent valves. The seats were clean and they seem to function fine when engine is rotated.

"Raider820" I plan to that do that before I pull the engine again just for curiosity sake! Fairly sure it's still good though, the backfiring has been constant even though I replaced it.

"Tinkerer200" I agree if the float is stuck open, the anti-backfire solenoid won't be very effective at stopping the flow. When I took the bowl off and clean the carb some, I may have inadvertently dislodged debris in the needle seat. I did find the anti-backfire stem slow to move and cleaned as well. YES, I have torqued all bolts to manual spec's including the flywheel bolt. The new key slide in nice. However I plan to check it again before I remove the engine.

"LawnRoyalty" Thank you first for the look at manual! When I took the engine apart I removed the crank gear and inspected both sides. The side facing up "with dot" was scared from I assume debris. I laid it on a flat sharping stone and polished it as much as a could to make it smooth with out removing allot of steel. The dot was revealed when I was through. I'm certain I installed it correctly as far as which side faces the sump. Now second guessing my self if the dots were exactly lined up.

Thanks for the responses. I will be checking flywheel key then moving on to pulling engine again. Taking pics this time! :)
 

Tinkerer200

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  • / Briggs & Stratten 20HP won't start, backfiring through exhaust and carb.
"I'm certain I installed it correctly as far as which side faces the sump."

One side of the inside of the crankshaft timing gear is beveled making it very unlikely to be able fit the sump on properly as incorrectly installed crankshaft timing gear will hold block and sump apart.

Walt Conner
 

StarTech

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  • / Briggs & Stratten 20HP won't start, backfiring through exhaust and carb.
Plus with backside being solid covering gear teeth the OP shouldn't be able to install it backwards and then install the camshaft.

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