More Lawn Mower Help Needed

"ttyymmnn" (ttyymmnn) 10/08/2014 at 11:59 • Filed to: None

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A few weeks ago I posted about my lawn mower ( !!!error: Indecipherable SUB-paragraph formatting!!! , !!!error: Indecipherable SUB-paragraph formatting!!! ), how it would start but not run. Now it won't start at all. I really, really want to fix this myself so I don't have to pay somebody else to do it, and I'm game to learn how. But I've done what I can to this point, and need some suggestions.

A few months ago, I replaced the fuel line. So fuel should be flowing to the carb. In the latest round of repair attempts, I replaced the spark plug and air filter, removed the carb bowl (it was quite clean) and sprayed copious amounts of carb cleaner in the carb and on the bowl. I also covered myself in gasoline (lesson learned). After that round of work, the mower would run, but only with the air cleaner removed. Two weeks ago, I got it to run only after tilting it all the way back (wheelie). Last week, it ran for two minutes and now won't even turn over.

Part of my problem is that I just don't know what could be wrong, or what parts could be causing the issues. I'm also up against a fundamental lack of knowledge about how these damned things work, though I understand the theory.

This shot shows the carb, with the air filter and air filter mount removed. You see the fuel line on the left, and the open-ended hose attaches to the back of the air filter mount. Is this where air gets sucked into the engine? As I said, I've cleaned the bowl and sprayed a lot of carb cleaner into the carb. I think I got the bowl reassembled properly last time because it did run long enough to get my front yard done.

Here's a top view of the carb. Just how much of this can I disassemble without screwing everything up, and what would I do if I got in there? Is this possibly not fuel-related at all, rather electrical? How can I test if I'm getting spark?

As you can see, I'm stumped. Thanks in advance.

chuck07 > ttyymmnn 10/08/2014 at 12:07

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Have you checked and changed the oil?

Isn't there a screw on the carb that controls the air/fuel mixture?

Agrajag > ttyymmnn 10/08/2014 at 12:09

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You can test for spark by removing the spark plug but keeping the wire and boot attached. Hold it against one of the cooling fins or something and have someone pull the cord. You will see sparks.

I know some people at a small engine shop I will ask them today.

ttyymmnn > chuck07 10/08/2014 at 12:09

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Oil is low, and needs to be filled/changed.

Isn't there a screw on the carb that controls the air/fuel mixture?

I don't know, is there?

RamblinRover Luxury-Yacht > ttyymmnn 10/08/2014 at 12:10

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The open-ended hose is crankcase ventilation. Pulls excess blow-by gases into the engine rather than blowing oily air all over the place.

The bowl can be perfectly clean, but you can still have a clog in the *screw*. The screw that holds on the bowl on most of these is a metering jet with a small orifice, and if that hole is clogged, you won't get any fuel.

As to how to check if you have spark, pull the plug, clip it in the boot, and just leave it resting against the engine. Briggs magnetos are pretty strong, so you should be able to see a spark. Obviously, if you see white crystals or profuse oil/carbon on the plug, that would a problem too.

Fundamentally, if it will fire and run briefly on carb cleaner sprayed down the throat, your ignition system is fine.

It is possible to have intermittent ignition timing issues from a partially sheared woodruff key on the flywheel. That happens if, say, you've hit a rock hard enough to stop the engine, but can happen pretty spontaneously as well.

ttyymmnn > chuck07 10/08/2014 at 12:11

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I don't mean to be a smart ass. I really don't know. I've know about adjusting mixture, but I don't know how to do it.

ttyymmnn > Agrajag 10/08/2014 at 12:12

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Thanks.

Big Bubba Ray > ttyymmnn 10/08/2014 at 12:12

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http://pull-start-my-heart.kinja.com/

Go there and ask Vince for help!

ttyymmnn > RamblinRover Luxury-Yacht 10/08/2014 at 12:13

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I checked the screw last time, and even though I could see through it I soaked it in carb cleaner anyway.

Plug is new, wire is clean inside.

No significant impacts.

ttyymmnn > Big Bubba Ray 10/08/2014 at 12:14

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I'm already an author there, and this was shared from PSMH. Thanks, though.

RamblinRover Luxury-Yacht > ttyymmnn 10/08/2014 at 12:14

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A lot of Briggs vertical engines aren't really designed to be tunable. I think it's all in the jet screw, being sized correctly for the given engine. They're meant to be idiot-proof in a number of respects - take for example that they have an engine-speed regulator (a tab blown by the flywheel) and no manual control for throttle.

crowmolly > ttyymmnn 10/08/2014 at 12:15

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Will it start or stumble if you spray it with starting fluid?

RamblinRover Luxury-Yacht > ttyymmnn 10/08/2014 at 12:17

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Most of the time if you have a sealing issue, it'll bleed gas, so that's probably not it. It is possible for the jets in the throat of the carb to clog up, but the screw clogging first prevents that most of the time. They *can* be cleaned with the wire from a bag tie. I assume your float valve is not sticking?

RamblinRover Luxury-Yacht > crowmolly 10/08/2014 at 12:20

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I like carb cleaner for that (or, at one place I worked, a Visine bottle of gas), because that helps narrow down the spark vs. fuel issue and is less likely to go bang.

crowmolly > RamblinRover Luxury-Yacht 10/08/2014 at 12:22

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Very true! Usually I fill an old zippo fluid tin with gas and squirt with that. Just figured he might have some ether on hand.

McMike > ttyymmnn 10/08/2014 at 12:23

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How can I test if I'm getting spark?

Remove plug

Attach wire

Touch bottom of plug to block/head (something metal)

Pull cord.

You should see the plug spark between the center and side electrode.

Please only hold the plug via the rubber boot for this, otherwise you'll be testing by feel.

ttyymmnn > crowmolly 10/08/2014 at 12:23

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Is starting fluid different from carb cleaner?

ttyymmnn > RamblinRover Luxury-Yacht 10/08/2014 at 12:24

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That's the white plastic piece inside the cup? No, it's working properly. When I had the cup off, I could push it up and fuel would flow.

RamblinRover Luxury-Yacht > ttyymmnn 10/08/2014 at 12:26

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The white plastic piece pushes on a needle that seats into a cone - when it's pushed up, the gas should stop, and when it's dropped, the gas will flow. Sometimes, a misalignment of the bowl or float, or decay of a rubber tip on the needle will cause the valve to stick, thus allowing you to run only until the gas in the bowl is used up. Probably not your problem, but one of the things on the Great List of Checking Things.

crowmolly > ttyymmnn 10/08/2014 at 12:27

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Yes. People use different kinds of fluids for this purpose; I said starting fluid since it's pretty common and I figured you might already have it. Some people use carb cleaner too to varying forms of success.

Starting fluid is pretty volatile and tends to really go bang, so if you have something to squirt a little bit of gas into the carb I'd do that. Just make sure it's fresh gas.

desertdog5051 > ttyymmnn 10/08/2014 at 12:30

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Possibly a float level problem. Does it smoke (black) when it does run on level ground? Spark plug black and sooty? Plug wire from magneto coil in good shape? Lots of possibilities.

chuck07 > ttyymmnn 10/08/2014 at 12:33

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I'm not sure. Some cars have the screw on there. It may control fuel flow. Look for a screw with a spring on it. If it is there you can play with it. It could also be missing.

RamblinRover Luxury-Yacht > McMike 10/08/2014 at 12:36

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As a note, holding the plug via the rubber boot is fairly often not "safe", because they decay and Briggs magnetos kick like a motherfucker.

ttyymmnn > desertdog5051 10/08/2014 at 12:40

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Lots of possibilities indeed! I still think this is fundamentally a fuel supply issue. I'm going to go back and chase/rechase some of these leads and see what I can accomplish.

No black smoke, btw.

RamblinRover Luxury-Yacht > desertdog5051 10/08/2014 at 12:40

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There's not any adjustment on the float level of a modern vertical shaft Briggs. Plastic float, plastic needle tab. No idle control/tuning screw IIRC, no throttle control (air-operated speed governor), and functionally automatic choking based on the governor. Simple, and meant to be cheap and disposable, but generally easy to fix as a consequence of the simplicity.

Trevor Slattery, ACTOR > ttyymmnn 10/08/2014 at 12:45

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These things will run in just about any condition provided there is spark. Spark is made and distributed by a magneto.

If you take the top off the mower you will see this assembly. The flywheel has magnets spaced along the smooth part that passes the ignitor.

When they sit, that flywheel and ignitor get covered in rust so electricity cannot pass. Clean the smooth part of the flywheel and the ignitor with fine sandpaper (You will see the shiny sport where the magnets are imbedded once you start to clean it). Should fire right up.

I dusted off my fathers 30 year old Toro which had been sitting for a decade. I cleaned out the float bowl and needle and seat in addition to cleaning up the magneto/flywheel and it started on the first pull.

Cheers!

McMike > ttyymmnn 10/08/2014 at 12:55

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If it was me, I'd starting taking shit apart until I found something dirty. Then I would fidget with it until is started running. That's very hard to explain over the internet, since fidgeting is hard to put into words.

So I'll keep watching Theremin videos.

McMike > RamblinRover Luxury-Yacht 10/08/2014 at 12:58

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Oh, in that case get a friend to help you.

RamblinRover Luxury-Yacht > McMike 10/08/2014 at 13:03

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Truth. A "friend", or as we like to say in these parts, "victim" or "unwitting dupe".

desertdog5051 > RamblinRover Luxury-Yacht 10/08/2014 at 13:07

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That's good to know. My 20+ yo lawn mower is pretty basic. That's good, I guess. I start it once or twice a year. Sometimes I cut down the tumbleweeds in the side yard. Nothing else to cut so it sits forlornly in a shed.

ttyymmnn > McMike 10/08/2014 at 13:11

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Slow day at the office?

McMike > RamblinRover Luxury-Yacht 10/08/2014 at 13:11

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Also required: the ability to hold in the laughter and say, "OMG, sorry about that!"

McMike > ttyymmnn 10/08/2014 at 13:28

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Yeah, our team lead often sends out something for us to review that always requires multiple questions in order to put it into context.

He's the king of answering only one question per email. If you ask two, one of them will be ignored, or (if they are similar enough) you won't be sure which one he's answering.

I have a list of questions, and send them off one at a time. It's painful, but it pays the bills and keeps me from wringing his neck.

I'm on question #3 now, waiting a reply.

Agrajag > ttyymmnn 10/08/2014 at 14:25

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The guy I spoke to thinks it is most likely a fuel quality issue(water). He said to pull the bowl again and drain all the fuel and then try fresh gas.

ttyymmnn > Agrajag 10/08/2014 at 15:09

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I just had a long chat with a friend who knows about these things and we decided that it is most likely a fuel starvation issue. I'm going to clean the carb again as thoroughly as possible and then, as you suggest, put new fuel in, though it's mostly good gas now. I'm going to give special attention to the carb bowl and jet screw. Thanks for asking. I probably won't get to it until tomorrow though.

Vince-The Roadside Mechanic > ttyymmnn 10/08/2014 at 17:16

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How is the compression on the motor?

ttyymmnn > Vince-The Roadside Mechanic 10/08/2014 at 17:21

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I have no idea. I had a long chat with a friend who is more knowledgeable than I am, and we decided that it's almost certainly a fuel starvation issue. I'm going to drain the gas and replace with fresh, check the float and clean it, make sure the jet is completely clean, and go after the carb again. The fact that it started and ran, even briefly, tells me that it's getting spark. But I think the fuel is either not getting to the cup or it's not getting to or out of the carb.

Vince-The Roadside Mechanic > ttyymmnn 10/08/2014 at 17:23

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If it started the compression is ok. The problem I run into most is that it will run off carb cleaner but won't run long enough to pull gas from the tank.

ttyymmnn > Vince-The Roadside Mechanic 10/08/2014 at 17:26

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I think that's exactly what is happening.

Vince-The Roadside Mechanic > ttyymmnn 10/08/2014 at 17:37

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Me too.

Mattbob > ttyymmnn 10/09/2014 at 13:59

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Does the carb have pilot screw? Last time I rebuilt a carb I made the mistake of screwing the pilot screw all the way in, effectively starving it of fuel.

ttyymmnn > Mattbob 10/09/2014 at 14:03

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Not sure what a pilot screw is. Here's the parts diagram for the carb:

Mattbob > ttyymmnn 10/09/2014 at 14:09

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have you looked at this guide? http://www.briggsandstratton.com/us/en/support/…

Mattbob > ttyymmnn 10/09/2014 at 14:11

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and this http://www.briggsandstratton.com/us/en/support/…

ttyymmnn > Mattbob 10/09/2014 at 14:17

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I have not! Thanks for the link.

Sally O'Broder > ttyymmnn 10/09/2014 at 15:33

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I remember having this exact problem and I apologize for not remembering the solution, but it did have something to do with doing some kind of prep on the air filter that I kept forgetting.

Also, and it's not going to be happy with you at first, try putting a bit of Marvel's Mystery Oil in it as well as some B12 Chemtool. SMALL AMOUNTS. I use B12 for all of my cleaning needs and it always gets the job done well as long as I'm cautious about it. Otherwise, Seafoam Deep Creep. >_>; Normally I'm not all for miracles in a can but neglected lawn stuff usually calls for it.

ttyymmnn > Sally O'Broder 10/09/2014 at 15:41

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I once knew the meaning of life but forgot to write it down.

I've heard folks talk about seafoam, so I'll look into it. Thanks.