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Briggs and Stratton blowing gas out carb

95335 Views 9 Replies 6 Participants Last post by  AVB
I have a Briggs model 407577 Type 0292 E1 21HP Intek V Twin engine that is blowing gas out of the carb and flooding the engine. The few times it has actually cranked gas flows out of the muffler and drowns the spark plugs. I took the breather off and tried to crank it and gas is blowing out the back of the carb through the choke assembly. At first I thought it was a float/needle issue so I've put in a new carb kit. No luck. A friend of mine thinks that the engine is building too much pressure and said he had heard that replacing engine gaskets would fix this. I'm no mechanic but pretty good with my hands so I'm trying to fix the mower without paying $55 an hour. Most everything I've read pointed to a bad carb float/needle other than a few strings on a possible crankcase gasket being bad. Any info would be appreciated. Thanks

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Take the carb back off and shoot a little starting fluid into the intake where the carb mounts. Start it up and watch what happens. If it blows back out the intake there is something wrong in the engine. If it starts up and runs until the fuel runs out then it's a carb problem. Process of elimination.
Sounds like it was stored with fuel in it for an extended period. Completely clean and rebuild the carb then check to make sure the intake valve is moving properly. If the engine started flooding over while it was in storage the old fuel may have formed a thick "varnish" on the intake valve stem causing it to stick open.
Thank you for the responses. It's been a while since I've gotten to work on it. I checked it this afternoon and when shooting starting fluid in the intake the mower will run without blowing it back out the intakes. It will run as long as I keep squirting fluid in. It does run wide open and is really smoking. I have replaced the needle valve and all that stuff in the carb but not the float tube fuel plastic piece. That's the piece that the inlet jet goes into. Do I need to replace those two pieces, I think that's all that's left to buy, or get a new carb. Thanks.

Look up your/the parts that you are refering to here so we can help you better.
After rebuilding my B&S carb, I still had the same problem. I then remembered that before the problem started I had connected a hose clamp on the lower hose (vacuum) of the fuel pump. I removed the clamp and this allowed for some air to seep into the vacuum line resolving the issue. It appears to me that creating a perfect seal on that vacuum hose, caused the pump to work more than necessary. I'm thinking of installing a valve to adjust it to the best peak performance. Let me know if you have had the same issue and how you fixed it.
Hi, :wave: and welcome to TSF.

Sorry to tell you but the OP hasn't been around for a while "Last Activity: 04-22-2011 02:41 AM"

Also, the main responder hasn't logged in for over a year.

You never know though, they may just get an email notification. :smile:
My response was for anyone that does a Google search and comes up with this site, that what I posted would help them. I would also like to add that after my posting, I viewed several YouTube videos on repairing the B&S carbs and I did not see any of the vacuum tubes have a clamp on.
My response was for anyone that does a Google search and comes up with this site,
Ahh, good thinking!

I'm sure one of our auto guys will be along shortly.
First this is old thread which why it wasn't never on my radar.

Never had problem with having the clamps all three ports of the Briggs vacuum fuel pump. Most likely the problem was due to a damaged float bowl gasket or fuel transfer tube o-ring. On the Nikki carburetor all it takes a small nick to cause problems. I have even have found bad bowl gasket in repair kits which is why I keep a couple spares on hand. Only one time I had to replace the transfer tube and that was because I put my big foot on it and broke the float hinge mount.
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