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Little backstory; had a bad carburetor blowing fuel out the intake. Ordered a new one and put it on and it stopped blowing fuel out the intake and ran fine. Drove around the yard 2 or 3 times and parked it. Went back to it about 2 hours later to run again and mow and it would not start again. Took off the cover to discover it was blowing fuel out the intake again. Think I just got a bad/cheap carb? Or other issue going on?

I don't think it's a carb problem, it may be a valve/valve timing problem.

Scrubcadet10 said:

I don't think it's a carb problem, it may be a valve/valve timing problem.

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I adjusted the valves and the flywheel key is not sheared.

All that a carb does is mix fuel with the air.
Blow back is caused by
1) stuck valve
2) valve out of times with piston
3) exhaust port / muffler blocked
4) blown head gasket / hole in piston

bertsmobile1 said:

All that a carb does is mix fuel with the air.
Blow back is caused by
1) stuck valve
2) valve out of times with piston
3) exhaust port / muffler blocked
4) blown head gasket / hole in piston

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Sounds like she’s getting opened up

Before you open it up, please provide us the all the engine numbers, so we can see what you are dealing with.

Rivets said:

Before you open it up, please provide us the all the engine numbers, so we can see what you are dealing with.

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Briggs 19.5 hp Model: 31P6770132B1; need anything else?

The compression relief hasn’t been working from time to time on start up. It will just half turn and stop. Have to cover the intake and get the engine gets turning fast enough to crank before I release. Wonder if this is causing the intake valve to stick open??
Thank for the help.

These engine are known for blowing head gaskets. If it were in my shop I would order a head gasket kit #794152 and replace the head gasket. First remove the valve cover and plug. Turn the engine over by hand and look to see if the valves are operating correctly. If they are remove the head, clean and replace the head gasket. Reinstall, torquing properly, and adjust the valves. Here is a service manual for the engine. https://docs.google.com/open?id=0B6NaqjIxWV1ybEN0LWo3azl6OUU. How you proceed is this is just my opinion.

Rivets said:

These engine are known for blowing head gaskets. If it were in my shop I would order a head gasket kit #794152 and replace the head gasket. First remove the valve cover and plug. Turn the engine over by hand and look to see if the valves are operating correctly. If they are remove the head, clean and replace the head gasket. Reinstall, torquing properly, and adjust the valves. Here is a service manual for the engine. https://docs.google.com/open?id=0B6NaqjIxWV1ybEN0LWo3azl6OUU. How you proceed is this is just my opinion.

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Valves are operately correctly. Went ahead and pulled the head to do the gasket. Going to check the compression relief as well while I am already working on it. We’ll see what I find tomorrow....

repperl said:

Valves are operately correctly. Went ahead and pulled the head to do the gasket. Going to check the compression relief as well while I am already working on it. We’ll see what I find tomorrow....

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You should see one of the valves bump a little, just before the compression stroke is at TDC, without having to open the sump.

Rivets said:

These engine are known for blowing head gaskets. If it were in my shop I would order a head gasket kit #794152 and replace the head gasket. First remove the valve cover and plug. Turn the engine over by hand and look to see if the valves are operating correctly. If they are remove the head, clean and replace the head gasket. Reinstall, torquing properly, and adjust the valves. Here is a service manual for the engine. https://docs.google.com/open?id=0B6NaqjIxWV1ybEN0LWo3azl6OUU. How you proceed is this is just my opinion.

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Looks like the head has cracks in it...where can I get a new quality head? Worth replacing?


Also signs of cracking in the pan...something to worry about?

looks more like casting marks from the factory to my eye.

Scrubcadet10 said:

looks more like casting marks from the factory to my eye.

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Gasket was thin in this area on the head, made me think it was cracking...I’m not sure

Right casting marks, nothing to worry about.

And for the third time they are shrinkage fins
If you run your finger over them they are raised up off the surface not sunken down into the surface .
When the castings come out of the mould they have a tough skin on the outside but are still partially molten inside
As the last bits solidify it causes the whole casting to contract and those fins are the result from it getting smaller as it cools from 800 C to room temperature.
Bigger flatter ones are defects in the mould surface that have been polished out and strait ones are join lines because some of these moulds are better than 20 little bits clamped together .
It is all about driving down the cost price for the customer .
They could use moulds & a casting cycle that ends up producing smooth surfaced castings but that takes about 5 times longer per casting and halves the service life of the moulds so just about quadruples the cost of each casting.
Way back when people would pay a proper price they polished off all of these but again that takes a long time & pushes up the price .
Ask a plastic surgeon , pretty is not cheap .