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Briggs and Stratton 19.5 hp engine. Blows fuel out the intake when trying to start, never starts. Have taken the carb apart 2 times and cleaned, no change. It do believe it has a bad decompression valve (it locks up when trying to start and I have to block off intake with a piece of carboard to "reset" it). My question is if the decompression valve is bad, could it be enough to blow fuel back out the intake valve? Should I start with fixing the decompression valve or new carb? Thanks,

Sounds like the needle in the carb is leaking, and excess fuel is getting in the engine.

Fish said:

Sounds like the needle in the carb is leaking, and excess fuel is getting in the engine.

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Everything visually looks okay in the carb. May just get a rebuild kit and see how it goes...

You might also remove the valve cover and crank the engine, and watch the action of your rocker arms. Make sure each one travels up and down about the same distance.

Fish said:

You might also remove the valve cover and crank the engine, and watch the action of your rocker arms. Make sure each one travels up and down about the same distance.

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What does it mean if the rocker arms are not traveling the same distance? Valve not seating all the way?

One of the cam lobes could be wiped out, i.e. the exhaust valve not opening, and the compression blowing back when the intake opens. Just doing simple tests and observing.

If you could take pics or a movie, then we could all see what you see.

Here is one with a lobe wiped out.

Pull the carb off the engine. Speay a small amount of starting fluid in the intake port and try to start. If engine fires up for a few seconds you have a carb problem. If it spits back out the intake port and doesn't start you have a valve or ring/cylinder problem.
I really don't know what you mean when you are resetting something putting cardboard over the intake.

Hammermechanicman said:

Pull the carb off the engine. Speay a small amount of starting fluid in the intake port and try to start. If engine fires up for a few seconds you have a carb problem. If it spits back out the intake port and doesn't start you have a valve or ring/cylinder problem.
I really don't know what you mean when you are resetting something putting cardboard over the intake.

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Good point. Or rather, disconnect the fuel line and then start the engine. Another possibility is that he has one of those carbs that has a main jet that falls out easily, and he lost it the first time he went through the carb.
Been there and done that.

Hammermechanicman said:

Pull the carb off the engine. Speay a small amount of starting fluid in the intake port and try to start. If engine fires up for a few seconds you have a carb problem. If it spits back out the intake port and doesn't start you have a valve or ring/cylinder problem.
I really don't know what you mean when you are resetting something putting cardboard over the intake.

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The engine has a compression release valve on the cam that helps with starting. (I had a problem with the engine appearing to have a slow start, similar to a bad battery, it would turn 1/2 revolution and stop). It has a new battery and starter performed on the bench. I found online that covering the intake doesn't allow the engine to build compression so that the engine can get turning, "bypassing" the broken compression release valve, then take off the cover so that it can attempt to start as normal. (This fixed that issue)

I just didn't know if the compression release being broken could cause issues of fuel going back out the intake. Since it opens the intake valve to bleed off compression at start.

I will give the starting fluid a shot and see what happens.

Fish said:

One of the cam lobes could be wiped out, i.e. the exhaust valve not opening, and the compression blowing back when the intake opens. Just doing simple tests and observing.

If you could take pics or a movie, then we could all see what you see.

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I already adjusted the valves and I think the rockers were traveling the same distance just from turning it over by hand, but I will check this again and get pictures.

I had a 17.5 opposed twin (flathead) doing the same thing ... blowing fuel out the intake/air cleaner upon attempted start-up.
A compression test told me which cylinder was dead (0 compression) . I pulled the head off to find an air cleaner to carb screw was lodged in the intake valve.... holding it open.
This allowed the pressurized fuel mixture to blow up the intake and out the carb.

I simply pulled the offending screw out with needle-nose pliers and it ran like a dream for many years!!!!!

bugdewde said:

I had a 17.5 opposed twin (flathead) doing the same thing ... blowing fuel out the intake/air cleaner upon attempted start-up.
A compression test told me which cylinder was dead (0 compression) . I pulled the head off to find an air cleaner to carb screw was lodged in the intake valve.... holding it open.
This allowed the pressurized fuel mixture to blow up the intake and out the carb.

I simply pulled the offending screw out with needle-nose pliers and it ran like a dream for many years!!!!!

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I may eventually have to open it up and see as well. Trying to eliminate everything before doing so.

Did you see the intake valve bump open when you watched the valves?

Scrubcadet10 said:

Did you see the intake valve bump open when you watched the valves?

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I did see that, which made me think the compression relief was still working. But, was still 1/2 turn and locking down every now and then. Makes me think its working sometimes and not others. Covering the intake to stop compression gets it going enough to were I can release and it cranks fine.

Scrubcadet10 said:

Did you see the intake valve bump open when you watched the valves?

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I also wonder if the intake valve is sticking open if the compression relief is bad. This would allow fuel back out the intake, correct?

Backing up a little bit, when did this start? did you use it one week, and then next week it wouldn't start?

Scrubcadet10 said:

Backing up a little bit, when did this start? did you use it one week, and then next week it wouldn't start?

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It all started when the fuel pump went out (checked and no fuel coming out of pump) replaced it and wouldn't start. Was doing the 1/2 turn and stop deal. Went to adjust the valves and realized it had dumped gas into the oil as well. Did an oil change and read online that the 1/2 turn and stop deal was a sign of bad compression relief valve and found the cover the intake trick, which works and it tries to start, just turns over and over.

Fish said:

One of the cam lobes could be wiped out, i.e. the exhaust valve not opening, and the compression blowing back when the intake opens. Just doing simple tests and observing.

If you could take pics or a movie, then we could all see what you see.

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here is a video of the valves. Looks okay to me, but I’m still new to this. As you can see, fuel mixed with the oil again, I’m going to assume it will need a new carb?

Oh, it's coming out there? I thought you meant back through the carb.
Drain that oil asap, change the filter if it has one, and rebuild or replace the carb

Good thing that you aren't a smoker!!

Scrubcadet10 said:

Oh, it's coming out there? I thought you meant back through the carb.
Drain that oil asap, change the filter if it has one, and rebuild or replace the carb

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It comes out the intake too. I checked the oil after my last attempt to start it and it wasn’t mixed. I think after trying to start it for an extended time it is flooding into the oil. I’m going to just get a new carb ordered, it’s only around $40