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View Full Version : Lawn Mower: how to empty "bad gas"


phungi
04-27-2008, 12:09 PM
I forgot to drain the gas from my mower this winter, which was a major blunder since I had it tuned up last year. So, it will not start, and I assume it is because of bad gasoline.

I don't want to take it into the shop and pay to have it drained/cleaned if it is something I can do myself. I consider myself pretty "handy" and have all the necessary tools.

Any recommendations from the SDMB handyman community?

astro
04-27-2008, 12:15 PM
I forgot to drain the gas from my mower this winter, which was a major blunder since I had it tuned up last year. So, it will not start, and I assume it is because of bad gasoline.

I don't want to take it into the shop and pay to have it drained/cleaned if it is something I can do myself. I consider myself pretty "handy" and have all the necessary tools.

Any recommendations from the SDMB handyman community?


In these scenarios I typically tip the mover over and dump the remaining old gas into a container then fill it with with fresh gas. The fresh gas when primed into the engine wtll typically make it kick over. You may also want to clean your spark plug connection.

Shagnasty
04-27-2008, 12:17 PM
If you are talking about a push mower, just flip it over, let it drain and fill it with fresh gas. It may take longer than normal to start but it will assuming there isn't something else wrong with it.

pkbites
04-27-2008, 12:22 PM
Push mower or ride on?

You could try dumping a bunch of HEET in it. I'm thinking some water may have condesated inside during the winter.

You could get one of those plastic hand pump siphons for a couple bucks and siphon it out.

Or get one of those big aluminum turkey pans at the dollar store and tilt the mower allowing the gas to run into the pan. Easier said than done, but it works.

Put some Stabil in the tank with fresh gas.

Are we talking about more or less than a gallon of gas?

Q.E.D.
04-27-2008, 12:28 PM
Once you get the gas tank emptied, the next thing you'll need to tackle is the carburetor. At the very least, you'll need to disassemble it and spray out all the orifices, jets and passages inside with a good quality carb cleaner to get rid of the varnish that stale gasoline turns into. If the varnish has heavily clogged the jets, you'll probably need to ream them out with piano wire of a suitable size. If things are really bad in there, you might need to get yourself a rebuild kit, which includes replacement gaskets, o-rings, needles and sometimes jets along with other parts. If there's a fuel filter (usually inside the tank, but sometimes inline between the tank and the carb), you'll also want to go ahead and replace that, as well.

Fubaya
04-27-2008, 12:43 PM
Let's first figure out if that really is the problem. What does it do when you try to start it? Did the mower spend the winter outside in a shed or inside in a garage?

engineer_comp_geek
04-27-2008, 01:16 PM
Gas does go bad, but in my experience a mower will run on gas left over from last fall. It may not run perfectly smoothly, but it will run. I think you've got another problem. QED gave excellent advice on the carb. You could also have a problem with spark. Check the plug and the wires for corrosion. I have a problem on one of my mowers with the automatic shutoff mechanism. The cable is getting a bit old and stretched and doesn't always pull it properly into the run position.

Xema
04-27-2008, 01:34 PM
Gas does go bad, but in my experience a mower will run on gas left over from last fall.
I concur that blaming the gas is premature. I'm with Fubaya - diagnosis before repair is always wise.

I own 6 gas-powered items: mower, 2 chainsaws, leaf blower, weed whacker, pressure washer. None has ever had the end-of-season gas treatment that I really ought to perform, and none has ever failed to start the next year. About the worst you can say is that it can be a bit harder to start something when it hasn't been run for months (but not infrequently even this isn't so). The "gas goes bad" notion probably becomes valid after more than, say, 12 continuous months of idleness.

Finagle
04-27-2008, 02:21 PM
Try removing the air filter and blowing some starter fluid into the carb. If it starts then, but continues to run rough, then maybe put some carb cleaner additive into the gas.

Cleaning and regapping the spark plug is an easy first step in any sort of engine-won't-start diagnosis.

phungi
04-27-2008, 07:30 PM
Thanks for the replies.

Here are more details:
-push mower, Briggs&Stratton Engine
-last started about October
-"tune-up" in August=new plug, cleaned out everything, ran fine after that

When I try to start it, it does not turn over. Nothing other than the sound of the pull-starter turning the motor.

I was careful not to over-prime it, and only pushed the bulb 2-3x and then gave it about 10 tugs, then another 2-3 pumps, repeated 10 tugs, and 2-3 pumps for a total of 4x then gave up. I checked the spark plug connection, which is clean.

astro
04-27-2008, 08:01 PM
Thanks for the replies.

Here are more details:
-push mower, Briggs&Stratton Engine
-last started about October
-"tune-up" in August=new plug, cleaned out everything, ran fine after that

When I try to start it, it does not turn over. Nothing other than the sound of the pull-starter turning the motor.

I was careful not to over-prime it, and only pushed the bulb 2-3x and then gave it about 10 tugs, then another 2-3 pumps, repeated 10 tugs, and 2-3 pumps for a total of 4x then gave up. I checked the spark plug connection, which is clean.

1: Pour out old gas fill with new gas

2: Check air filter

3: Check cables and position of choke to make sure nothing is sticking

3: Prime the hell out of it - Push it 10 times - then begin trying to start it with heroic pulls.

If it's not even *trying* to kick over I'd remove the plug entirely and check for carbon buildup or oil contamination.

Kevbo
04-27-2008, 08:32 PM
If it is an old B&S where the tank IS the fuel bowl, then a turkey baster would be my tool of choice. If you must turn it upside down, then drain the oil first, and fill it with clean afterward. (good idea to change it each spring anyway) Inverting an engine (especially a worn one) is a good way to get the cylinder full of oil which will foul the plug.

If the carb is fed from the tank via a fuel line, the disconnect the line and drain the tank via the outlet.

Harmonious Discord
04-27-2008, 08:51 PM
Why do you people want to flip the mower upside down? The oil runs out too. Just remove the fuel hose from the carburetor and drain the gas into a container. The gas tank is usually held onto the motor housing with a couple screws. remove it if you feel the tank needs cleaning.

Q.E.D.
04-27-2008, 08:59 PM
The oil runs out too.
Not on any mower I've ever owned. You pretty much have to invert them to clean them.

amarone
04-27-2008, 09:46 PM
Gas does go bad, but in my experience a mower will run on gas left over from last fall. Mine didn't this year. Replacing the gas was an easy and cheap thing to try - I just tipped it over and let the gas run into a container. Then I refilled with new gas and bingo - it started no problem.

Carson O'Genic
04-28-2008, 03:44 AM
I concur that blaming the gas is premature. I'm with Fubaya - diagnosis before repair is always wise.

I own 6 gas-powered items: mower, 2 chainsaws, leaf blower, weed whacker, pressure washer. None has ever had the end-of-season gas treatment that I really ought to perform, and none has ever failed to start the next year. About the worst you can say is that it can be a bit harder to start something when it hasn't been run for months (but not infrequently even this isn't so). The "gas goes bad" notion probably becomes valid after more than, say, 12 continuous months of idleness.

A heads up for you.I've noticed the ethanol blends "stale" in short order, two months maybe, especially noticeable in chain saws.Prior to blended fuels my observations concur with your statement.

Harmonious Discord
04-28-2008, 06:30 AM
They don't mount the gas tank on the carburetor. I guarantee there is a connecting piece of hose or tubing going from the tank to the carburetor. You may not see it but it's still there. You may have a shroud over it, but it's there. Get out your parts diagram if you need to.

I've had to buy the more expensive blends in the last year for the small engines to run properly. I think it's the ethanol being a problem too.

Xema
04-28-2008, 06:58 AM
I've noticed the ethanol blends "stale" in short order, two months maybe, especially noticeable in chain saws.Prior to blended fuels my observations concur with your statement.
Thanks - worth noting. I've shied away from ethanol blends due to concerns about damage to hoses and gaskets. But it's getting harder to find "E-free" gas.

masterofnone
04-28-2008, 10:28 AM
Definitely diagnose the problem before assuming it's bad gas. Is the oil low? Some engines have a low oil cut off (though I've never seen it on a lawnmower).

An engine needs air, spark, and gas. Air and spark are quick + easy to check. Make sure the air filter is clean, and look into the carb to see if the choke is functioning. Remove the spark plug, hold it by the rubber boot with the side or end grounded to the engine. Pull the starter and look for spark. May as well clean and gap the plug while you've got it out. Once you know you have air and spark, then it's safe to assume it's the fuel system. I've never had gas less than a year old prevent me from starting anything - it just makes it hard to start and it runs rough (Never used blended fuels though). I suspect varnish in the carb or fuel filter. I agree with Q.E.D. re. the carb cleaning, except that I would go ahead and get the rebuild kit if it has been more than a year since the last rebuild. They're cheap, and if you are going to take the carb apart, you might as well freshen everything up.

I had a generator in the shop last winter, and the guy told me that started fluid was bad for the engine - anyone know why?

gotpasswords
04-28-2008, 01:10 PM
Thanks - worth noting. I've shied away from ethanol blends due to concerns about damage to hoses and gaskets. But it's getting harder to find "E-free" gas.
That's impossible in some states. California, for one, will require at least 10% ethanol in all pump gas by the end of next year, but most refineries are already producing E10. Minnesota plans to require 20% ethanol in 2013. On the plus side, the ethanol is being used to replace MTBE, which brought in a pile of other problems.

If you want to be sure of getting ethanol-free fuel, you're probably limited to going to an airport to get some 100LL avgas. This will probably only work if you get there in an airplane.

As for getting bad gas out of equipment - my neighbor had to do this just yesterday. He filled his 4-month old mower with gas that was left over from last year, creating an instant dead mower.

He wound up disconnecting the fule line from the bottom of the tank to drain it, then unscrewing the large nut that holds the float bowl on the carb just enough to drain the carb. Put it all back together, filled with fresh gas, and was back in business. No flipping, tilting or other acrobatics needed.

Tom Tildrum
04-28-2008, 04:34 PM
Just FYI, last spring (after the first year I ever owned a lawn mower), I drained old gas out of my B&S engine by turning it upside down. The oil did apparently leak into the works, because for a while after that, when I ran the mower, there would be intervals where it would belch out great clouds of gray smoke. I looked like the Once-ler, from The Lorax.

At the end of the season, I was careful to use up the existing gas in the mower tank as much as possible. This spring, I had only a little old gas waiting in the tank, and I just poured enough fresh gas over it that I had no trouble starting it.

Mr. Duality
04-28-2008, 09:41 PM
Old gasoline need not be thrown away or poured on the ground (shudder). You can mix old gas in with a much larger amount of fresh gas and all will be well. A gallon or two of old gas can be added to your car's (mostly full) gas tank with no ill effects. So say The Car Guys on NPR, and I've found it to be true.

It's a safe bet that your power equipment will last longer and run better if you prepare it for off-season storage in accordance with instructions in the owner's manual.

Mr. Duality
04-28-2008, 09:51 PM
Helpful hint: when tipping your mower on its side, tip it so the air cleaner is up. If you tip it so the air cleaner is down, oil may soak the air cleaner which will prevent starting until the situation is rectified.

Max Torque
04-29-2008, 09:40 AM
Mine didn't this year. Replacing the gas was an easy and cheap thing to try - I just tipped it over and let the gas run into a container. Then I refilled with new gas and bingo - it started no problem.
Same here. Wouldn't start on the stuff in the tank (I'd left it about half full all winter), so I tipped and drained it, put in fresh gas, and it started on the first pull. Magic.

Then, I mowed the side yard to get the engine nice and warm, shut it down, and did a full spring service on it: drained the warm oil and refilled it, replaced the spark plug, and replaced the air filter. Briggs & Stratton makes a maintenance kit for their engines that makes it all easy; I think they sell it at Home Depot. In one box, you get the oil, plug, and filter, plus a little tube of gas stabilizer for the winter, if you can remember where you put it. Just pick the kit that covers your engine's horsepower rating, and you're golden.

Aestivalis
04-29-2008, 02:01 PM
I was lazy this year, so I filled the nearly empty tank on my Craftsman mower with the oil/gas mixture from my snowblower. Forty or so pulls later, it started, and didn't have any problems with the lawn. Maybe I'll get it serviced before I put it away in the fall! :)