Carb bowl won't fill, needle valve and tank vent seem fine

[Dr. Brapp]

I'm pretty new to small engines and I'm trying to get a Tecumseh powered lawn mower running that I got for free. Like the title says, the carb bowl isn't filling at all, and I don't know why. Here's what I know so far:

• The bowl doesn't fill at all. Even after leaving it overnight the bowl is empty in the morning.
• If I start with a full bowl, it runs fine for a minute or 2 before stalling.
• The needle valve seems to work. When I take the bowl off, fuel starts trickling out of it. When I disconnect the fuel line from the tank and spray carb cleaner into it, it comes out of the needle valve.
• The tank is vented well enough. With the tank disconnected and the fuel cap on I can pour fuel smoothly out of its outlet.
• When I move the float, the needle valve moves with it. If I lift the float, it stops the flow of fuel. If I let go of the float, it falls down with gravity and fuel starts trickling out again.
• The float doesn't have a spring. I don't know if it's supposed to have one or not.
• The float is made of plastic.

There you have it. It acts as if the needle valve is closed, but only when the bowl is installed. What could cause this?

 

[ILENGINE]

My firs thought would be float height set too low and hitting the bottom of the fuel bowl shutting off fuel flow. Also have to be careful about using carb cleaner because it will cause the rubber float valve seat to swell stopping fuel flow also.

 

[Rivets]

Agree with IL, but will add that you can adjust the float height by bending the float tab.

 

[Dr. Brapp]

I didn't measure it but the float height looked OK. It's very possible the needle valve seal is swelled up though, I'll check it out. Will ethanol gas cause that? The nearest gas station doesn't have ethanol-free premium so I didn't use it.

 

[Rivets]

Most times I recommend that the carb is removed from the engine to check float height. Unless you have a great eye, or a way to measure height on both sides, it’s just a guess. Most times it is a swelled seat which causes the change.

 

[sgkent]

What has already been said. Also replace the fuel line. Sometimes the hose can have a piece inside partially blocking where it slides onto the carb. Also some engines have a small fuel pump that runs off a vacuum so without a model number it is hard to know if your engine is one of those or it is gravity fed.

 

[Rivets]

Tecumseh mower engines do not have fuel pumps!

 

[ILENGINE]

I didn't measure it but the float height looked OK. It's very possible the needle valve seal is swelled up though, I'll check it out. Will ethanol gas cause that? The nearest gas station doesn't have ethanol-free premium so I didn't use it.

Ethanol won't swell the rubber donut seat but carb cleaner can make it double in size. Also on Tecumseh the float when properly set doesn't set level. You should be able to slip a 11/64 drill bit between the float and the carb body without the bowl gasket installed. The float sets an an angle with the side opposite the float pin closer to the carb body then the pin side.