Posted: 5/20/2011 12:34:22 PM EDT
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My damn lawnmower crapped out on me last week. I had just finished mowing and it lost power and died, I could get it started, but it would only run if I held the deck at a 45* angle.
So I finally have some time to take it apart yesterday. But I cannot get the damn thing to run. Its a craftsman self propelled mower, with a briggs and stratton engine. So far I have pulled the carb and cleaned it out. Used compressed air to blow out all the ports. Needle and O ring were perfect. Float good. Bowl was filled with gas. Didnt do anything to help. Then I pulled the gas tank off and blew out the line, cleaned the tank. Its flowing adequatly. This didnt help either. Then I suspected a spark problem. So I pulled the plug and grounded it. Had my wife pull the cord. Which she could not pull very hard. I didnt notice a spark. So I pulled it apart and set the gap on the stator (think thats what its called). The gap between the flywheel and the arms was about 1/4". I set the gap to 0.010 This did not do anything as well. I also inspected the grounding wire. It was intact. I also cleaned the grounding wire contacts. Nothing has helped yet. I am starting to think that there is a stuck valve. When I had the engine apart to check the electricals, I was turning the flywheel by hand and plugged the spark plug hole. I did not notice compression or suction. I am to the point of ripping the head and cylinder off to see if thats the problem. Anyone else have ideas of what to check before I get to far? It will run if I spray starting fluid through the carb. I get about ten seconds before it dies. I am thinking there is not enough vacume to pull the gas through the valves. I have 3 summers on the mower. to add. Gas is less than a month old. Tried starting with both the air filter on and off. |
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Oddly enough, small engine repair is something I leave to the repair folks, but I'll work on our vehicles' engines all day every day.
I had a similar problem with my old pushmower except I traced it back to the gasket that surrounds the primer bulb/air filter. Gasket was shot, engine wouldn't pull fuel into the cylinder. I replaced the gasket ($30) and it runs fine. You can try having someone hold their hand over the primer bulb "pocket" while you crank the engine...if it runs, you found the problem. |
| When you were checking the stator gap, did you check the plug wire to make sure the shroud hasn't chaffed through it somewhere? I had that happen once on a BS engine and it drove me crazy trying to trouble shoot it. It would run erratically, and tilting it like you describe did make a difference. |
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Make sure the ignition system is working. Could be a stuck valve or leaking. If it is a side valve B&S, the head is easily removed to check. Or you can pull the breather (rectangular cover, two screws) and turn the engine over. But removing the head is best since you can also see the valve seats and condition. Corrosion of the valve/seat will cause this. A small bit of lapping compound will get the valves to seal and takes minutes, just make sure to completely clean. |
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I will check the plug wire.
It doesnt have a priming bulb. Kind of a goofy set up for a mower. No priming bulb, no throttle control. Just pull the cord and thats it. My wife picked it out a few years ago when our cheapy walmart mower died. I will see if I can pull some more info from the engine. I have taken apart and put together the upper portion of the mower so many times, that I can do it in less than five minutes. Not sure how I feel about being that profecient at it 
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Oh, and if an overhead valve, they are just as easy to lap the valves. You don't need a spring compressor, I've done it without. Just don't lose the keepers, a magnet will help as will an assistant to pick out the keepers. Putting it back together is easier with a dab of grease on the keepers. If this is a diaphragm carb, ethanol in gasoline can cause these to harden, then the carb won't pump the gasoline into the bowl which will make it run poorly. If the carb is mounted on the gas tank, this is the problem! Get a carb overhaul kit and never store it with gasoline. |
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I will check the plug wire. It doesnt have a priming bulb. Kind of a goofy set up for a mower. No priming bulb, no throttle control. Just pull the cord and thats it. My wife picked it out a few years ago when our cheapy walmart mower died. I will see if I can pull some more info from the engine. I have taken apart and put together the upper portion of the mower so many times, that I can do it in less than five minutes. Not sure how I feel about being that profecient at it Well Johnson we may have found the problem. 
My wife picked out my push mower and it's been a massive pile for the three seasons I've had it. It was my "birthday present". It's red and has a "husky" engine on it. It's nickname is "the travesty" after Walter Sobchek. |
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Oh, and if an overhead valve, they are just as easy to lap the valves. You don't need a spring compressor, I've done it without. Just don't lose the keepers, a magnet will help as will an assistant to pick out the keepers. Putting it back together is easier with a dab of grease on the keepers. If this is a diaphragm carb, ethanol in gasoline can cause these to harden, then the carb won't pump the gasoline into the bowl which will make it run poorly. If the carb is mounted on the gas tank, this is the problem! Get a carb overhaul kit and never store it with gasoline. If it's an OHV Briggs and Stratton OTS motor, he'll probably find that the valves are totally out of adjustment. I had one of those motors on a 700 dollar TORO that was so bad that I gave it away for free after a year and a half of misery. The valves were so awful on that thing that the start up routine was check the gas, check the oil and adjust the valves...not kidding, it sucked that bad. |
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Quoted: Quoted: Oh, and if an overhead valve, they are just as easy to lap the valves. You don't need a spring compressor, I've done it without. Just don't lose the keepers, a magnet will help as will an assistant to pick out the keepers. Putting it back together is easier with a dab of grease on the keepers. If this is a diaphragm carb, ethanol in gasoline can cause these to harden, then the carb won't pump the gasoline into the bowl which will make it run poorly. If the carb is mounted on the gas tank, this is the problem! Get a carb overhaul kit and never store it with gasoline. If it's an OHV Briggs and Stratton OTS motor, he'll probably find that the valves are totally out of adjustment. I had one of those motors on a 700 dollar TORO that was so bad that I gave it away for free after a year and a half of misery. The valves were so awful on that thing that the start up routine was check the gas, check the oil and adjust the valves...not kidding, it sucked that bad. I've noticed that too. General poor assembly quality on those engines. Like fuxored gasket flange surfaces, piss poor valve lash adjustments (they do use aluminum pushrods on the intakes to stabilize lash) and piss poor rocker arm centering on the valve stems. Since the rocker pedestals set rocker arm centering, it IS adjustable, you just need to properly HOLD the square shank of the pedestal while tightening the bolt holding it to the head. The pedestal will then emboss its teeth into the head and stay put. Also, a bit of thread sealant on this bolt will keep the head cleaner since oil loves to weep through these threads, gumming up the head. Other issues with OHV B&S are the nasty intake runners. I've cleaned them up, removing flashing with die grinder and a brake cylinder hone. Yeah, really getting the most from these engines...a port and polish job. |
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Oh, and if an overhead valve, they are just as easy to lap the valves. You don't need a spring compressor, I've done it without. Just don't lose the keepers, a magnet will help as will an assistant to pick out the keepers. Putting it back together is easier with a dab of grease on the keepers. If this is a diaphragm carb, ethanol in gasoline can cause these to harden, then the carb won't pump the gasoline into the bowl which will make it run poorly. If the carb is mounted on the gas tank, this is the problem! Get a carb overhaul kit and never store it with gasoline. If it's an OHV Briggs and Stratton OTS motor, he'll probably find that the valves are totally out of adjustment. I had one of those motors on a 700 dollar TORO that was so bad that I gave it away for free after a year and a half of misery. The valves were so awful on that thing that the start up routine was check the gas, check the oil and adjust the valves...not kidding, it sucked that bad. I've noticed that too. General poor assembly quality on those engines. Like fuxored gasket flange surfaces, piss poor valve lash adjustments (they do use aluminum pushrods on the intakes to stabilize lash) and piss poor rocker arm centering on the valve stems. Since the rocker pedestals set rocker arm centering, it IS adjustable, you just need to properly HOLD the square shank of the pedestal while tightening the bolt holding it to the head. The pedestal will then emboss its teeth into the head and stay put. Also, a bit of thread sealant on this bolt will keep the head cleaner since oil loves to weep through these threads, gumming up the head. Other issues with OHV B&S are the nasty intake runners. I've cleaned them up, removing flashing with die grinder and a brake cylinder hone. Yeah, really getting the most from these engines...a port and polish job. You're more talented with that kind of stuff than I am Keith. I just bought a Honda motor and all my troubles went away.
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Oh, and if an overhead valve, they are just as easy to lap the valves. You don't need a spring compressor, I've done it without. Just don't lose the keepers, a magnet will help as will an assistant to pick out the keepers. Putting it back together is easier with a dab of grease on the keepers. If this is a diaphragm carb, ethanol in gasoline can cause these to harden, then the carb won't pump the gasoline into the bowl which will make it run poorly. If the carb is mounted on the gas tank, this is the problem! Get a carb overhaul kit and never store it with gasoline. If it's an OHV Briggs and Stratton OTS motor, he'll probably find that the valves are totally out of adjustment. I had one of those motors on a 700 dollar TORO that was so bad that I gave it away for free after a year and a half of misery. The valves were so awful on that thing that the start up routine was check the gas, check the oil and adjust the valves...not kidding, it sucked that bad. I've noticed that too. General poor assembly quality on those engines. Like fuxored gasket flange surfaces, piss poor valve lash adjustments (they do use aluminum pushrods on the intakes to stabilize lash) and piss poor rocker arm centering on the valve stems. Since the rocker pedestals set rocker arm centering, it IS adjustable, you just need to properly HOLD the square shank of the pedestal while tightening the bolt holding it to the head. The pedestal will then emboss its teeth into the head and stay put. Also, a bit of thread sealant on this bolt will keep the head cleaner since oil loves to weep through these threads, gumming up the head. Other issues with OHV B&S are the nasty intake runners. I've cleaned them up, removing flashing with die grinder and a brake cylinder hone. Yeah, really getting the most from these engines...a port and polish job. alot of their new stuff is so bad the first oil change comes out looking like bass boat paint because of all the casting flash coming out of the crankcase. And then theres stuff like forgetting to put all the magnets in the flywheel and the motor pops with less than 100 hours on it, etc..... im glad i dont have to fix that shit anymore. |
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yeah they're cheap as shit motors, but they run. Are you getting compression? if you are its not a stuck valve. Check it with a $20 compression testor if you can't tell by rotating the crank by hand and feeling if too much air is escaping the cylinder.
But I'm thinking carb. Are you sure all the pathways are clear? Compressed air doesn't really do much for getting crap out out of the pathways. Use a torch tip cleaner these problems 95% of the time are carb or electrical |
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Another thing about B&S engines. They use a diamond cylinder hone on their cast iron bore liners. While this sounds great, diamond hones are not good for surface finish, tending to gall excessively, making a less than uniform cross hatch depth This leads to oil consumption issues since deep score marks are left long after rings seat. Old style aluminum oxide hone stones leave a much better finish since the hone is constantly exposing sharp abrasive as it breaks down. This keeps the swarf (removed material) from galling and making deeper score marks. |
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Well, I pulled the top end off the engine, valves looked fine. Both open and closed while turning the flywheel. I have compression while turning the flywheel by hand.
I also pulled the intake runner off and its clear. I did notice the valve seal retainer was almost off. I took pics, but my stupid smartphone decided not to save them. I reassembled it, and gave it a try. With no damn luck. Also, when I cleaned the carb. I could see light through the main jet. There is no pump on the thing. It must run off of gravity and engine suction. |
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Quoted: Well, I pulled the top end off the engine, valves looked fine. Both open and closed while turning the flywheel. I have compression while turning the flywheel by hand. I also pulled the intake runner off and its clear. I did notice the valve seal retainer was almost off. I took pics, but my stupid smartphone decided not to save them. I reassembled it, and gave it a try. With no damn luck. Also, when I cleaned the carb. I could see light through the main jet. There is no pump on the thing. It must run off of gravity and engine suction. Is the carb attached to the fuel tank? If so, it indeed has a pump and overflow type bowl. |
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Well, I pulled the top end off the engine, valves looked fine. Both open and closed while turning the flywheel. I have compression while turning the flywheel by hand. I also pulled the intake runner off and its clear. I did notice the valve seal retainer was almost off. I took pics, but my stupid smartphone decided not to save them. I reassembled it, and gave it a try. With no damn luck. Also, when I cleaned the carb. I could see light through the main jet. There is no pump on the thing. It must run off of gravity and engine suction. Is the carb attached to the fuel tank? If so, it indeed has a pump and overflow type bowl. I looked. It has a line that goes from the tank to the carb bowl. The bowl sits under the carb. I took the entire thing apart, and saw nothing that would resemble a pump or anwhere it would hook onto the engine. |
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If it has a Champion spark plug get rid of it they are junk. Go down to a parts store and get anything but a Champion. Only thing I have not replaced. I should of done that first. Quoted:
Does the mower have a zone start cable that grounds the coil?? You said no spark correct?? No spark with wife pulling. Its kind of hard to do by myself
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Will it fire on carb spray?? Yep, would run for a few seconds |
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I figured it out.
I thought it might have something to do with the EGR, so I took this apart. But the valve seemed to work as intended. 
Then I took the carb apart again and ran a needle throug the ports, finishing up with compressed air. As I was putting it back together, I noticed the bolt that holds the bowl onto the carb had holes in it. As the carb fills, it would raise the gas to the main jet. The tube leading to that had slots machined into it. I didnt realize the bolt would completely plug that tube. I just assumed the slot would allow the gas to fill the tube. The holes in the bolt that holds the bowl onto the carb had gas flowing through them. I cleaned them out, and blew some air through them. It started up on the second pull. Only took me six hours to figure this out. 
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Well, I pulled the top end off the engine, valves looked fine. Both open and closed while turning the flywheel. I have compression while turning the flywheel by hand. I also pulled the intake runner off and its clear. I did notice the valve seal retainer was almost off. I took pics, but my stupid smartphone decided not to save them. I reassembled it, and gave it a try. With no damn luck. Also, when I cleaned the carb. I could see light through the main jet. There is no pump on the thing. It must run off of gravity and engine suction. Is the carb attached to the fuel tank? If so, it indeed has a pump and overflow type bowl. I took some pics of the fuel delivery system. Tank with tube. The silver thing is an extension I shoved in there to keep the gas from spilling everywhere. 
Carb inlet. This leads to the needle and float. 
Other side of the carb. 
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Yep, that is a float type carb, fuel flows by gravity. And yes, junk can plug the bottom of the jet. I've installed a B&S fuel shutoff valve on my mower so the carb can be run dry after each season, this way the gasoline won't clog it up when it dries out over the winter. Or worse, the bowl is aluminum and can corrode. Voice of experience here. |
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Spark, fuel, and compression are what a mower needs to run. spray some ether into the spark plug hole, reinstall spark plug and give it a pull. no fire means your missing either spark or compression you need somebody who can pull the cord for you while you ground the plug and look for a spark ETA: I saw it'll run with ether, so it's probably the carb... |