Help with B&S Fuel Pump

jon11April 22, 2009

I'm looking for some help with a fuel pump on a Cub Cadet LT1018 lawn tractor. The engine is a 18.5 HP Briggs and Stratton. It looks like the engine model number is ELS500.

The fuel pump has a fuel line from the tank and a fuel line to the carb., but it also has an oil line running from the oil fill tube. I don't understand why a fuel pump would have an oil line?

The problem started as an oil leak from the fuel pump when the engine was under a heavy load (bagging tall grass). Now the oil leak has gotten worse and the engine will only run with the choke pulled all the way out. I assume the fuel pump is not getting enough fuel to the carb?

This is the second time it has happened. Has anyone ever heard of this? Anything that could be causing the problem other than a faulty fuel pump?


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"but it also has an oil line running from the oil fill tube. I don't understand why a fuel pump would have an oil line?"

That line to the oil fill tube is a vacuum line to operate the vacuum fuel pump. Fuel pump may have bad diaphragm.

Walt Conner

    Bookmark   April 22, 2009 at 9:28PM
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Okay, thanks. Sounds like I'm just having bad luck with fuel pumps.

Thanks again for the help.

    Bookmark   April 22, 2009 at 9:38PM
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Are you checking your oil level? IF gasoline is leaking past the float needle and contaminating the oil, making it over full and thin, this will cause these symptoms. IF you have had multiple incidents of this. I would suspect that. B&S oil level is checked with the dipstick screwed in.

Walt Conner

    Bookmark   April 23, 2009 at 8:17AM
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I was having the same problem before and after an oil change. When I changed the oil a couple of days ago, I started with 40 oz. of oil instead of the required 48oz. to be sure it wasn't overfilled. According to the dipstick it was at the bottom of the "safe" range. I still had oil leaking from the fuel pump. Before changing the oil and after I noticed the problem, the oil level was even lower because of the leak.

I just picked up another fuel pump. Nobody at my local repair shop had ever heard of the problem.

    Bookmark   April 23, 2009 at 9:26AM
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jon11, is this pump made from plastic or metal? Be sure to inspect the vacuum hose that connects to the pump. Look for cracking or splitting of the hose. If the hose is cracked, split, or otherwise perforated, oil can leak out near the pump (and possibly "onto" the pump) causing it to "look like" the pump is leaking. You might also want to inspect the old pump to see if the body of the pump has a crack in the shell. Both a defective pump, or hose, can result in an oil leak. The "vacuum" hose in this case furnishes "pulsed vacuum" to the pump. The "pulses" are created as the engine piston(s) moves up and down in the cylinder(s). This phenomenon could be called "alternating pressure/vacuum pulse" because it alternates from a slight pressure to a slight vacuum constantly. The "pressure" portion of the cycle will get greater when the engine is under a load, due to increased "engine blow-by". If the pump and hose are free of defects, the pulse cycles only move into the vacuum hose from the engine (pressure half of cycle) and then right back out of the hose on the vacuum half of the cycle. If the pump or hose has a crack or perforation, oil mist will be transported to the crack and leak out during the pressure half of the cycle. The leak will be greater when engine is under a load than when it is idling. Just make sure you try to identify whether it is a bad pump or a bad hose.

    Bookmark   April 23, 2009 at 10:22AM
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The pump is plastic. I originally thought the leak was coming from the connection between the hose and the pump. I changed the clamp (used a screw clamp) but nothing changed. After taking a closer look while the engine was running I noticed that the oil seems to be coming out of a small round metal screen on the pump itself.

Based off of your comments I think I will replace the vacuum line also just to be safe.


    Bookmark   April 23, 2009 at 4:58PM
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I am having the same exact problem with my Briggs 16HP on my Ariens Zoom 1640. Did you ever fix the problem? If so please post.


    Bookmark   May 13, 2009 at 12:58PM
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I to have a Briggs 16 HP with oil leaking from the fuel pump. The oil level is actually at the add mark. There is no oil in the breather. After reading the posts. I will replace the pump which is only a year old as well as the hoses to determine if this solves the problem. If any one has additional info I would appreciate it. There was a post by skmnh with a similar mower and engine. I wonder if his problem was solved.

    Bookmark   April 25, 2010 at 3:58PM
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Hello jon11. Did the new fuel pump solve your problem? I am having the same issue with my Briggs & Stratton 18.5 hp ELS 500 OHV. The oil is definitely leaking from the small round screen on the face of the fuel pump.

    Bookmark   May 15, 2010 at 7:13PM
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same problem with my briggs 16hp. eventually stopped running. found fuel lines inside tank broke down and cracked apart. Turns out to be from all the ethanol they put in the fuel now. rigged up lines to the bottom of the tank but they leak. Wonder if they are causing the pump to suck oil with the fuel???

    Bookmark   May 15, 2010 at 8:52PM
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You have a leaking head gasket. It will be leaking between the cylinder and pushrod galley, This is a common issue with these engines, the leaking gasket will pressurize the crankcase and force oil into the vacume line for the fuel pump. There are a couple ways to confirm, first remove the spark plug and look at it, it may be built up heavy with carbon . second is to remove the vacume line from the fuel pump and see if there is oil in it, this will help confirm the head gasket issue.

    Bookmark   July 11, 2010 at 1:01PM
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I will bet you that you have a bad head gasket. I had the same problem on a 16 HP Briggs Intek. I replaced the fuel pump with no luck. A service repair individual told me about the head gasket. When It was replaced the problem was solved.

    Bookmark   July 26, 2010 at 2:01PM
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I have a 17hp briggs (1742 zero turn airens) I replaced the short block and on the old block I had two breathers comeing off the block the new block only has one so I conected it with a hose clamp to line off pulse pump will this work and was that tube off the block to be connected to air cleaner if so will it work this way ?

    Bookmark   May 2, 2011 at 2:01AM
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What happened to all the punctuation marks?
Is the replacement short block a used one or is it new?
The crankcase breather assembly on the block must connect to the air cleaner housing.
The vacuum pulse hose for the fuel pump would have connected to the other port on the block.
If this replacement engine was bought locally (to you) you need to take the issue up with the seller (because one expects to be sold a compatible product).
If you are trying to utilize a different engine, be advised that there are a few different ways to get a vacuum pulse hose connected to the engine to operate the fuel pump.
Probably the easiest way to "add" a vacuum pulse hose for the fuel pump is to find a valve cover from a junked engine and put that valve cover on the head.
Small engine shops might have a valve cover on a junked engine that they would (maybe) give you. Or you could sing for them.

    Bookmark   May 2, 2011 at 10:05AM
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I posted yesterday (3-22-12)that my cub Cadet model lt1018 was leaking oil from fuel pump.Well after replacing the fuel pump,guess what,thats right oil leak still there.But today (3-23-12)I found the real problem,a blown head gasket on the valve chamber side of the cylinder,which in return was putting compression into the crank case pushing oil through vacuum line from dipstick tube to fuel pump. After head gasket replacment problem fixed. NO MORE OIL LEAKING FROM FUEL PUMP!

    Bookmark   March 23, 2012 at 8:41PM
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We also have a Briggs & Stratton 18.5HP ELS500 motor on my mower. We originally replaced the fuel pump, did not help, then I found info on here about blown head gasket. We just replaced that and it is STILL blowing oil out of the center of the fuel pump. Someone suggested that the breather may be bad, but we checked that and it is fine. Is there anything else we can check, it only has 179 hours on it?

    Bookmark   July 25, 2012 at 3:06PM
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I have a Cub Cadet LT1018 with a Briggs 31Q777-0305E1. I ran across this thread while researching my problem, so I thought I would share my experience (and my stupidity) for others to learn. My fuel pump was leaking gas last summer, so I replaced it with the Briggs part. It started leaking gas again this fall, so this time I used an aftermarket part from Oregon. I installed the pump, and the engine started up just fine but then I started noticing white smoke. I shut the engine off and got a huge backfire (repeated this 2 more times and it backfired each time). I then parked it and let it run for 10 minutes but the white smoke started getting bad. I turned on the blades and a huge puff of white smoke came out. Then the motor died and wouldn't restart. I checked the oil and it was low. I then took off the carb and the carb was full of oil. I drained the oil and the oil smelled like gas. Based on the info from this web site, I assumed I had a blown head gasket, so I removed the head. I did have a blown head gasket, so I replaced it but the engine still wouldn't start. At first I assumed the carb was jacked up from all of the oil but then I decided to inject gas into the carb bowl...surprise, the engine ran for 10 seconds. Next step, pull the fuel line that runs from the pump to the carb and see if fuel is was not. Fast forward a few days of thinking and I realized that I accidentally reversed the pulse and fuel input lines when replacing the pump. I was sucking oil from the crank and sending it straight into the carb. I switched the lines and everything works great now. Well, I also change the oil twice and the oil filter once.

The only thing I couldn't figure out was: How was the engine even running with these lines reversed? All I can figure is this. Right before the fuel pump change, I topped off the gas tank to the very very top. I think that the gas was just running to the carb due to gravity. Once the tank got a little lower, the motor stopped because it had no gas. It had no gas because gravity could no longer feed the carb. In a way, this was a good thing because if the engine had kept running, I would have burned all oil and blown the motor.

    Bookmark   November 25, 2012 at 8:54PM
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Stuff like that is one of the reasons I highly recommend the use of a digital camera or just a phone camera and take pictures BEFORE you start taking things loose.
Alternative method is to sketch out how things like wires and hoses are routed and connected.
Every so often a story like this comes in to lend credence to what I have been stating. Live and learn, think and learn quicker.

    Bookmark   November 25, 2012 at 9:49PM
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