Engine cuts out between 1/2 and 1/4 tank

[Robj]

Craftsman T1600 46" deck lawn tractor. Briggs 19hp 540cc Model 33R8 77 0007 G1

Engine cut out - would crank but wouldn't fire. I checked and it had spark. I modified the fuel cut-off solenoid and it started. It ran great but would stop running again at 1/4 tank. Soon it became a 1/2 tank and it would either studder and die or just abruptly stop. If you fill the tank, it fires right up and runs perfect until the fuel level goes down again. I completely removed the solenoid and it's all the same. Stopped running at 1/4 tank now back to 1/2 tank. I just finished mowing today. Shortly before I finished, it started stuttering as it does. I turned off the blade and it pulsed for a bit like it was searching for an idle speed before smoothing out and it ran fine until I was done.

It has a new fuel filter. I've checked the tank and it's perfectly clean inside- there's no debris floating around getting in front of the outlet hole. It does not appear to have a fuel pump. The fuel tank is under the hood mounted above the carb with the main fuel line running to a nipple directly above the bowl. It appears to be gravity fed. I removed the fuel line from the carb and drained off some fuel. There's great flow. There is another line from the top of the fuel tank that connects to the runner between the carb and air filter. I assume this is some sort of an vapor capture emission system? The oil level is fine. I don't know if it has an oil level kill switch like my generator.

Any help would be appreciated. I can't understand why it runs perfect on the first half of the tank and won't run on less than half a tank.

 

[Hammermechanicman]

What type of fuel filter are you using?

 

[Robj]

It’s an in-line with a plastic housing. It was doing this with the old filter too which was the factory one.

I just took out to finish off a spot I had to leave from this morning due to swarming bees. I topped it off and it ran perfectly.

 

[bertsmobile1]

Typical of a build up of debris in the fuel tank or a swollen lining in the fuel line.
When it starts to run bad, pull the fuel line off & the cap then blow back through the fuel line
Problem goes a way = floating debris
A bad cap vent can some times do the same thing but generally it would cause the engine to die after 10 minutes or so.
Easy check for that is to run with the cap loose about 1/2 to 1 turn.

 

[Robj]

I’ll check it out. I’ve tried restarting it after taking the cap off and putting it back on and no go. It wants that full tank. But I’ll try that.

 

[Hammermechanicman]

Try removing the fuel filter and see what happens.

 

[Robj]

Ok

 

[Born2Mow]

Typical of a build up of debris in the fuel tank or a swollen lining in the fuel line.
When it starts to run bad, pull the fuel line off & the cap then blow back through the fuel line
Problem goes a way = floating debris
A bad cap vent can some times do the same thing but generally it would cause the engine to die after 10 minutes or so.
Easy check for that is to run with the cap loose about 1/2 to 1 turn.

True....

• Install all new fuel lines marked "SAE J30" because the alcohol attacks the older style "rubber". This also applies for the hose to the vacuum operated fuel pump, if present.
• The new EPA approved vent caps block easily.

 

[ILENGINE]

@Born2Mow In this guys case the fuel cap is non vented and is using a vapor recovery system. Which I suspect could be slightly restricted causing some of his issues, but he also tried removing the cap and didn't have an effect on his problem. But I have seen issues with certain fuel filters being too restrictive when operated in combination with the low tank vapor operation.

 

[Robj]

I’m going to replace the fuel lines and the vent line and filter and we’ll see where it goes from there. I get good gravity flow of fuel through the lines and the filter when disconnecting the fuel line from the nipple on the carb but if the inside of the lines are bad perhaps something is moving around in there. Perhaps the vent fitting on top of the tank where the vapor recovery line is attached is plugged.
I’m still baffled as to why I can have half a tank of fuel and it won’t start. I take the cap off and look down in the tank and see it’s clean in the bottom by the outlet opening, crank the engine again and it still won’t start. I fill the tank and it fires right up. We have a lot of property to mow before fire season so it’s not just s one time fluke. It’s been happening with every fill up. It seems clearly that it’s a gravity thing but then at half a tank I have great flow with the fuel line disconnected at the carb. It’s got me scratching my head.