B&S 18.5 HP Twin circa 2000

[HeadScratcher]

I have a B&S 18.5 hp Twin circa 2000 on a Huskee 46" cut rider. Recently I've been having problems with the engine running fine for 45 minutes or so and then it starts to act like it is running out of fuel. I have changed the fuel filter, air filter, verfied the vent on the gas cap was clear, checked for vacuum leaks, checked and regapped the spark plugs, checked for compression issues, rebuilt the carb and fuel pump, changed the oil, and checked for electrical issues, all to no avail. What am I missing? Any Ideas? I'm scratching my Head!!!

 

[bertsmobile1]

you are missing floating debris & in particular grass clippings that have accumulated in your fuel tank and get sucked into the outlet eventually forming a plug restricting fuel flow.
When you turn the engine off, they float away
You can double check either by setting up an alternative tank with more than 45 minutes of fuel in it . or an alternative fuel tank to plug in the instant your engine starts to faulter or if the engine stops, spray some carb cleaner down the carb.
If it fires right up then stops when the carb cleaner runs out , you have confirmed lack of fuel.
If your mower has a solenoid on the carb, this may be failing , quite rare but I have seen one that overheated and shut off after an hour or so .

 

[DaveTN]

Welcome to the LMF! I saw an 8N Ford gas tractor have the problem berts mentioned. Someone
had left a rag in the tank. Start it up fine, run a few minutes and it would sputter and die. Let it sit for a
few minutes and it would start again. Who the devil left a RAG in there? I've seen bugs of all
kinds down in the gas tanks on riding mowers. How do they get in there?

 

[bertsmobile1]

I ended up causing a marriage split when I accidentially mentioned the same problem with a customers mower was several condoms in the fuel tank.
Sort of explained why HE spent so much time in the detached workshop that was on the fence line & near a gate into the neighbours yard
Usually it is grass
The fuel displaces the water in the clippings and they become almost transparent so you don't see them when you look down the filler cap .

 

[DaveTN]

I ended up causing a marriage split when I accidentially mentioned the same problem with a customers mower was several condoms in the fuel tank.
Sort of explained why HE spent so much time in the detached workshop that was on the fence line & near a gate into the neighbours yard
Usually it is grass
The fuel displaces the water in the clippings and they become almost transparent so you don't see them when you look down the filler cap .

LOL funny about condoms in the tank! I could imagine the reaction the customer had. Stupid idea to put the
condoms in the tank tho.

 

[bertsmobile1]

So you would be thinking strait after a naughty with the neighbours wife / daughter ?

 

[HeadScratcher]

you are missing floating debris & in particular grass clippings that have accumulated in your fuel tank and get sucked into the outlet eventually forming a plug restricting fuel flow.
When you turn the engine off, they float away
You can double check either by setting up an alternative tank with more than 45 minutes of fuel in it . or an alternative fuel tank to plug in the instant your engine starts to faulter or if the engine stops, spray some carb cleaner down the carb.
If it fires right up then stops when the carb cleaner runs out , you have confirmed lack of fuel.
If your mower has a solenoid on the carb, this may be failing , quite rare but I have seen one that overheated and shut off after an hour or so .

Thank you for the tip. The gas tank appears clean, no debris that can be seen. I'll remove the fuel filter and lower the hose from the tank to see if gas comes out. If that appears ok I'll try the secondary fuel tank.
No solenoid on the carb.
I guess I should have mentioned that after setting for 20-30 min it will start and run for another 30min or so. It almost acts like a vapor lock but with rubber fuel lines I don't think that would happen.
I'll pull the cowl and make sure the engine doesn't have gunk built up on it just to make sure it isn't an overheating issue. Thanks again for the info. I'll keep you all posted.

 

[Tinkerer200]

Welcome from east central Illinois. When asking an engine question it is always helpful to post the model number. There are multiple 18.5 hp B&S engines totally different.

Walt Conner