Briggs - Gas Blowing Out of Carb

[GAVolunteer]

Briggs Engine 127802-0640-01 95091859
Carb has primer bulb
Toro Push Mower

Problem-Symptoms:
1. Engine starts and runs great for a few minutes and then runs "rough" for 15-20 seconds and then runs smooth for another minute or so and then runs rough again.
2. After troubleshooting, I noticed that the new paper air filer was wet with gas and the bottom of the air cleaner base was wet with gas.
3. With the air filter removed, the engine runs great and does not sputter or run rough.
4. With the air filter removed, I noticed a heavy mist of gas is blowing out of the carb. I believe when the filter gets wet with gas, the engine gets starved for air and then runs rough.
5. I put a known good carb in the engine and the second carb did the same thing.

Question: What causes gas to get blown out of the carb? How do I trouble shoot this?

Background.
1. The owner of the mower was mowing in very tall gas and "hit something". This caused the dipstick to get blown out of the tube spraying oil everywhere. He could not get the mower restarted and ended up breaking the pull rope.
2. I checked the flywheel and the key was not sheared. It looked fine.
3. I cleaned the carb, changed the oil, new spark plug, new rope.
4. I checked the blade and it was not damaged. I sharpened the blade and made sure it was balanced.

Thanks for your help.

 

[Michael72]

Key in blade adapter ok??...it might be a key or key-way built in to adaptor

 

[bertsmobile1]

Briggs Engine 127802-0640-01 95091859
Carb has primer bulb
Toro Push Mower

Problem-Symptoms:
1. Engine starts and runs great for a few minutes and then runs "rough" for 15-20 seconds and then runs smooth for another minute or so and then runs rough again.
2. After troubleshooting, I noticed that the new paper air filer was wet with gas and the bottom of the air cleaner base was wet with gas.
3. With the air filter removed, the engine runs great and does not sputter or run rough.
4. With the air filter removed, I noticed a heavy mist of gas is blowing out of the carb. I believe when the filter gets wet with gas, the engine gets starved for air and then runs rough.
5. I put a known good carb in the engine and the second carb did the same thing.

Question: What causes gas to get blown out of the carb? How do I trouble shoot this?


Thanks for your help.

The decompressor opens up to the inlet which blows back through the carb.
This only happens at cranking speeds.

Excessive blow back can be causes by valves being out of time with crank which will also cause rough running

Roug running can be caaused by out of time spark, check the flywheel key

 

[GAVolunteer]

Roug running can be caused by out of time spark, check the flywheel key

Good suggestion. I did a visual check on the key the other day. It looked ok. It may be slightly sheared which would explain everything. I'll remove the key and put in a new one.
Thanks

 

[Tinkerer200]

Key in blade adapter ok??...it might be a key or key-way built in to adaptor

Don't understand this connection?

Walt Conner

 

[Michael72]

Don't understand this connection?

Walt Conner

Just pointing out that when we know that the blades hit something that we auto look at flywheel key and sometimes the key or key-way in blade adapter is sometimes overlooked.

 

[GAVolunteer]

I replaced the flywheel key and retested. Fine mist of gas still came out of carb.

Checked the valve clearance. Intake valve was .0025. Exhaust .007. Removed head and valves. Cleaned carbon buildup which was not too bad. Lapped the valves. Carefully filed down intake valve stem to .006 clearance. New head gasket and valve cover gasket.

I thought fixing the intake valve would fix the problem, but it did not. Mower still has fine mist of gas coming out of the carb. It hits the metal plate on the air filter base and with the air filter removed, collects at the bottom of the cover and eventually drips in the deck. If the air filter is installed, the filter soaks up the gas.

Any other ideas or suggestions? The gas issue is a real safety concern. Thanks for the help.

 

[lugnut1]

first guess: would have been float, needle and seat issue.
(but you changed carbs and still have same issue.)

second guess: would be timing issue.

third guess: blow bye past rings (being you did valve's)
I'd do a compression check on it, and or a leak down test.

 

[upupandaway]

Briggs Engine 127802-0640-01 95091859
Carb has primer bulb
Toro Push Mower

Problem-Symptoms:
1. Engine starts and runs great for a few minutes and then runs "rough" for 15-20 seconds and then runs smooth for another minute or so and then runs rough again.
2. After troubleshooting, I noticed that the new paper air filer was wet with gas and the bottom of the air cleaner base was wet with gas.
3. With the air filter removed, the engine runs great and does not sputter or run rough.
4. With the air filter removed, I noticed a heavy mist of gas is blowing out of the carb. I believe when the filter gets wet with gas, the engine gets starved for air and then runs rough.
5. I put a known good carb in the engine and the second carb did the same thing.

Question: What causes gas to get blown out of the carb? How do I trouble shoot this?

Background.
1. The owner of the mower was mowing in very tall gas and "hit something". This caused the dipstick to get blown out of the tube spraying oil everywhere. He could not get the mower restarted and ended up breaking the pull rope.
2. I checked the flywheel and the key was not sheared. It looked fine.
3. I cleaned the carb, changed the oil, new spark plug, new rope.
4. I checked the blade and it was not damaged. I sharpened the blade and made sure it was balanced.

Thanks for your help.

From your symptoms, the gap in the valve train between the tappet and valve is too small. When u start it the gap is fine and as it heats up the gap closes too much and u get a valve left open and it sprays gas out to the filter leaving a puddle of gas. Remove the air filter and hold a sheet of paper over the air intake and it is blowing(spraying gas) the paper up instead of suck down is not normal.

To keep it simple, what i did is get a big screwdriver to pry the valve open and slipped in a file to grind it down a little and check with a feeler gauge .06 for intake and .08 exhaust i think... dont quote me on these numbers.

Don't know why but all 4 briggs 12hp i have found did this shortly after acquiring them. The last one i did about 6yrs ago, knock on wood.

Still what leaves me scratching my head is i dont see how hitting tall grass will stretch a valve but that is what the symptoms point to.

 

[Tinkerer200]

What often happens is some pertain fact is accidentally overlooked, omitted.

Walt Conner