Briggs gas starvation

[Steve Kraus]

I'm having problems with my generator powered by a 8 horsepower Briggs.* I I needed it the other night and it ran okay for 10 minutes and suddenly stopped. From then on it would only run briefly and wheezing only with the choke in, as though needed to help suck fuel.

Later when I had the chance, I dismantled the carb and the bowl was empty. So I cleaned and reassembled it and did some testing today. I wanted to check the fuel flow from the tank to make sure the screen isn't plugged there so I disconnected the line and let it run into a gas can. It stopped flowing after a bit. When I undid the gas cap flow resumed.

Here's the gas cap:

Where is the vent on it? I presume venting is part of the cap (hence the metal splash deflecting shield) and not elsewhere on the tank. Obviously something is gummed up.

I may have other issues too but this is a start.

*190412 3156-01 (new in 1992)

[Molly Brown]

Is there any possibility that the fuel line collapsed and is restricting the flow? Does the fuel line look cracked and worn out?

[Steve Kraus]

No, it flowed freely when the cap was off and trickled to a stop when the cap was replaced. So I presume there was no way for air to get in to allow gas to come out. As I said I may have other issues elsewhere with that engine but right now I'm just trying to figure out this situation which is only involving the tank and hose. Obviously both the strainer screen and the shutoff valve under the tank are fine if it was flowing freely with the cap off.

So I need to know where there is some sort of vent pinhole that has gotten clogged.

[LSMFT]

Check the cap and see if that metal flapper is stuck. If you can't see how it vents, drill a hole in it about 1/32". You don't drive it around so it won't leak.

[Stormin Mormon]

You'd be better off to replace the cap, and be done with it.

In the future as a work around, you can leave the cap slightly loose.

[Oren]

I have the same cap as the OP on a power washer. I looked for a vent hole but it is not to be found.

I found this view of a similar cap, but noted it does have a vent hole in the middle.

[Steve Kraus]

The best guess I can make is that it is allowed to vent along the threads. The rubbery gasket on mine has a couple of notches so maybe those are to keep it from being a total seal. And of course the metal plate is to deflect away as much splashing as possible. Maybe under some circumstances residue from evaporated gasoline can block this. On mine the rubber was pretty flat to the interior of the plastic cap. Maybe it needs to be looser.

[Oren]

Sure. Just back the cap off 1/8 turn after tight. That would break the vacuum and allow fuel to flow.