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Hi

Im new to this forum and hopeful I can find some help for an elderly friend of mine. I know next to nothing about mowers

My friend has an older craftsman ride on mower with a Briggs & Stratton 12.5 HP motor. Sorry I don't know the model numbers...

The problem he is having is that after starting it runs for maybe 20 seconds before gas starts to overflow into the filter and then the motor cuts out.
The gas seems to be coming through the vacuum line that is attached to the cover over the valve springs.

This is what I have tried

1. Installed new carb
2. New fuel filter
3. New fuel shutoff valve

Still the same problem. I thought it might be the carb needle not seating but they new carb would suggest not. I suppose its possible the new carb has the same issue.

I also took of the valve cover to check for a stuck valve but the intake and exhaust valve open and close as I rotor the engine. It also appears that they are closing properly. There was some carbon buildup.

Can anyone help with diagnosing this issue and a possible fix?

Thanks

Dean

Unless you bought the carb from a genuine mower shop or genuine mower parts retailer on line then it is 50:50 for the new carb being good .
Clean the old carb according to the photo instructions you will find at outdoor power info
when finished turn it upside down & try to blow in the fuel inlet, you should not be able to do it.
If you can then the needle & / or seat needs replacing .
Place it on the mower then crank the engine.
You should be able to stop the fuel flow by lifting up the float and that should happen before the float gets to the end of its travel .
Check the float bowl of the new carb.
If there are small blacks specks of rubber in there then replace all of the fuel lines .

dis00 said:

The problem he is having is that after starting it runs for maybe 20 seconds before gas starts to overflow into the filter and then the motor cuts out.
The gas seems to be coming through the vacuum line that is attached to the cover over the valve springs.

Click to expand...

Dean -
If fuel is coming out the vacuum line, then fuel has entered the engine.... where it is diluting the engine oil... and the stage is set for the engine to be destroyed. We don't want that !

Suggested approach...

1. Check the engine oil dip stick. The engine may be over-filled. The dip stick probably smells like gasoline. Drain and change the engine oil and engine oil filter. Add all new 10W30 oil (or other as recommended).
2. Install a fuel filter and a manual fuel shut off valve to the fuel line. Both pieces will be around $10-$12. Trash has entered the carb and allowed excess fuel to flow into the engine. This could be dirt from years of mowing or minor rust inside the tank. No need to diagnose, the fuel filter will remove all future trash. The manual fuel ON/OFF valve will stop all fuel flow while the engine is not running. Together these will eliminate any reoccurrence.
3. Remove the carb's float bowl
4. Remove the float and float needle. Turn ON the gas and trash will (usually) be completely washed out.
5. Reinstall the needle and float. Turn gas ON. Check that lifting the float stops fuel flow.
6. Reinstall float bowl.
7. Crank engine.
8. Cut grass.

Hope this helps.

bert and born above have the right things to do. Here's why..

Almost every lawnmower engine has a way of auto shutting off if it tips over, the way it shuts itself off is the oil from the crnkcase will flood into the intake and choke out the motor.. therefore, if the float on the old carb and/or new carb was stuck open to a point that you saw gas in the airfilter that means it first filled up the crankcase with gas and the oil level now (gas/oil mixture) is above the shutoff tunnel and is flooding the new carb..

Change the oil, disassemble the carb, clean it all up real good, reset the needle in the bowl of the carb.. refill oil and you should be golden..

mitchstein443 said:

bert and born above have the right things to do. Here's why..

Almost every lawnmower engine has a way of auto shutting off if it tips over, the way it shuts itself off is the oil from the crnkcase will flood into the intake and choke out the motor.. therefore, if the float on the old carb and/or new carb was stuck open to a point that you saw gas in the airfilter that means it first filled up the crankcase with gas and the oil level now (gas/oil mixture) is above the shutoff tunnel and is flooding the new carb..

Change the oil, disassemble the carb, clean it all up real good, reset the needle in the bowl of the carb.. refill oil and you should be golden..

Click to expand...

Yeah i never heard that before.
Usually there is a seat switch that kills spark when the operator leaves the seat with blades engaged. Much faster that way too.
The reason gas was coming from the air filter is because when the needle failed, the gas came out of the main jet and probably any other vent or idle passage in the carb and flowed out the filter, and into the combustion chamber.

dis00 said:

The gas seems to be coming through the vacuum line that is attached to the cover over the valve springs.

Click to expand...

Scrubcadet10 said:

The reason gas was coming from the air filter is because when the.....

Click to expand...

He never said that.

Born2Mow said:

He never said that.

Click to expand...

dis00 said:

Hi


The problem he is having is that after starting it runs for maybe 20 seconds before gas starts to overflow into the filter and then the motor cuts out.

Click to expand...

i assumed he means the air filter?

Scrubcadet10 said:

Yeah i never heard that before.
Usually there is a seat switch that kills spark when the operator leaves the seat with blades engaged. Much faster that way too.
The reason gas was coming from the air filter is because when the needle failed, the gas came out of the main jet and probably any other vent or idle passage in the carb and flowed out the filter, and into the combustion chamber.

Click to expand...

I hdn't either... until I accidently over filled my kohler engine 22hp.. it would run great but once warmed up would hesitate, stuuter nd eventully stall..

I figured, coil going bad, replaced it. samething happened..

Then figured must be the head gasket, which i had replaced a years back..

When I ent to drain the oil I found gas in it.. when I took the carb apart I found oil/gas in the throat...

I posted about it and was told it was a standard "feature" on riding mower engines to have a path for the oil to cause a fowl to shut off the engine in the event it turns over... And aparently this is since at least 1972 since it happened on both my dyt4000 with kohler single piston engine and my 1972 jd 400 with side by side double pistons.. I had to learn it ain't a car, it can't take 4 quarts of oil.. lol but if you want to give it try, over fill your oil by a quart or so and see how well the engine runs.. then drain it back down to norml level and see how well it runs.. on my 1990's dyt and my 1972 kohlers it happened, and I was told it is the same on all riding mower engines...