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Little Briggs Runs out of Fuel


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05-16-09, 07:01 PM   #1  
Little Briggs Runs out of Fuel

Hi guys,, Hope we can figure this out, as I'm sure I'm missing something simple. (not the first time for me!!) I have a Mod 96902 Typ 3148 01 Code 92051151 Briggs that runs great for 3 to 5 mins & quits.. I replaced the plug & verified I have spark right to the last turn of the crank. It starts with several primes, runs 3 to 4 mins & quits. I replaced the diaghragm in the carb & cleaned everything, Same.. Removed the primer & cleaned the check ball & seat under it.. Same.. The Owner brought a used replacement carb /tank that I put on,, Same,, Put the new diaghragm in the used replacement,, Still the same. The "O" ring @ the intake is new, The primer will pump fuel & the engine runs like a top for a few mins & quits.. I am verifing spark with an air gap tester & it's there till the flywheel stops... I'm Beat now unless anyone has any Ideas.. Thanks again for all the help,, Sorry for the long post...Roger

 
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05-16-09, 07:09 PM   #2  
So you're watching spark as it runs, correct? If it's not losing spark, then it's losing fuel or the flow of or compression of air. Does it start right back up? You have to prime several times to start it back up? How much of an air gap is the spark jumping across?

I believe I have seen a coil fail in such a way that it still fired, but it fired at the wrong time, but this would be very uncommon. I speculated it was due to semiconductors in the triggering device that heated up and got delayed somehow.


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05-16-09, 07:38 PM   #3  
Yes, I'm watching the spark as it runs & the air gap on the tester is about .020 inline with the plug gapped @ .030.Nice steady blue spark, Right to the Bitter End. 5 or 6 primes will start it back up again & the run time will be about the same.. It won't start after it quits unless it's primed,, almost as it has to fill the little "well " the main jet sits in in the fuel tank assy. This carb seems so simple, but it has me Baffled (but that's not hard to do either, LOL..) The engine seems solid & runs well when it does run,, no smoke, noises, etc..Thanks Cheese,

 
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05-16-09, 07:44 PM   #4  
Strange. Are you certain the diaphragm and gasket are in the right order? (tank, then diaphragm, then gasket, then carb). I believe it is a fuel problem and is related to the carb assy, even though this is the second one with the same symptom. That's the kicker.


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05-16-09, 07:56 PM   #5  
I definetly have them in the order of Tank,, Diaghragm,, Gasket,, then Carb.. I have ran it with a carb cleaner kinda stuff in the fuel thinking it may wash something out,, & blew out (both) carbs with a spray cleaner & compressed air, making sure I didn't get anywhere near the checkball under the primer, except to clean it with the spray cleaner.. I'm at a loss here, but I can answer lots of questions,, I'm on my way to Compression test it now as a last grasp @ the straw..LOL... Many Thanks,, Roger

 
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05-16-09, 08:13 PM   #6  
After 5 or 6 good pulls I'm getting about 100~105 psi compression on a cold engine. I forgot to mention that I have checked the flywheel key at the start of this,, just in case something hapened to it, but it was as new,,, Thanks,,, Roger

 
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05-16-09, 09:23 PM   #7  
That should be enough compression for it to run ok.

I don't know why I didn't think of this earlier, but loosen the gas cap. I've seen several of these with clogged vents in the cap and it will do exactly as you've described.


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05-16-09, 10:41 PM   #8  
Thanks Cheese, the gas cap dribbles fuel out when the tank is full & the engine is running,, I'm thinking if the fuel can get out, air can get in,,BUT maybe not?? now that you mention it... I'll try it again tomorrow & let you know if it's better with the cap really loose... Thanks for the tip 'cus the replacement tank/carb didn't come with a cap,, I used the one that was origional to the mower. This may be the common part between everything?? (Like I said,,Probably something simple, just I can't see it in front of me..LOL)... Lets hope ,,I'll let you know tomorrow 'cus the neighbours have no sence of houmor when I run lawnmowers @ 1:00 in the morning.. Go figure... Thanks,, Roger

 
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05-17-09, 06:36 AM   #9  
I was going to say the gas cap, too. Also, have you checked the gas for water? I know it is something stoopid & simple, but I have had a few mowers in the shop this year that had just enough water in the gas to run for 1- 2 minutes before sucking up a bubble of straight water that killed it. It would start up immediatly after then die again in a minute. We have been running E-10 here since Jan. 1 2007 and this crap has been causing tons of problems. Marinas had an exclusion, but that ened this year and now they, too will be using E-10.

 
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05-17-09, 08:54 AM   #10  
I checked the gas cap & if I get the right angle I can actually see daylight right thru it.. The gas is fresh as in less than a week old & I had cleaned the tank before I put it on.. I haven't seen any sign of water up 'till now, But just to be safe, I'll put some of the water remover stuff in that I keep for snowblowers..... Roger

 
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05-17-09, 03:20 PM   #11  
Since the problem has gotten to the head scratching stage I will suggest something I have only seen once on a new mower, on the main jet(under the thimble) the upper holes had little bits of plastic still clinging to the inner part of the tube on one side and was working as a flap, it would run until the debris blocked the jet, I caught it by pure accident, light reflection. Something to check. Have a good one. Geo

 
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05-17-09, 06:17 PM   #12  
Thanks, Geo... Are you saying I should remove the Main jet that sits in the "thimble"?? I've never pulled this out of this type of carb,, but maybe I'll find out how tonight.... Thanks,, I'll look into it & experiment with the old carb before I fly into the serviceable one... Thanks again, Roger

 
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05-17-09, 07:08 PM   #13  
Here we go, pry the jet out with a small screwdriver, I use the rounded end of the screwdreive handle to re-insert, some times it can be a little stubborn to snap into place. Here are the pics. Have a good one. Geo





 
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05-17-09, 09:09 PM   #14  
Geo, the pics are awesom & help a lot.. I didn't get a chance to tear into it yet... hope to tomorrow,,, Is there another 'O' ring @ the top of that jet??? Just so I know when I pull it out to look for it.... (or not) I Thank you again & I will let you know what I find tomorrow night,,, Roger

 
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05-18-09, 09:48 AM   #15  
The only "O" ring is at the bottom. Have a good one. Geo

 
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05-18-09, 08:42 PM   #16  
No Luck??? I tore into it again tonight & as Geo showed me,, I pulled the main jet out to clean it.. it looked clean, But I did give it a blast of spray carb cleaner followed with compressed air.. The"O" ring looked as new as well... I'm thinking it's about time to throw in the towel as I have way more time into it than I could ever get out of it... I just really HATE to let a piece of machenery beat me.. NOW I'm getting Stubborn,,,, LOL.... Thanks Again guys,,, Roger

 
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05-18-09, 09:04 PM   #17  
This sounds stoopid, but the B&S sites says " Why does my engine start and then shut down? The most common cause for this failure is old/stale untreated fuel or perhaps a sheared flywheel key (ignition timing)."
Everything else was the usual suspects (heated up coil, vapor locking, stale gas) and the engine is not runnig long enough to heat up the coil and with that carb set up it rules out vapor lock and fresh gas has been used.
So what's it going to hurt to check the keyway?

 
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05-18-09, 09:27 PM   #18  
It won't hurt to check, but I don't feel the flywheel key is the problem if it's running flawlessly when it runs and does not attempt to kick back when starting. Still won't hurt to look.

Something else to check: Look at the intake pipe from the carb to the engine, where it bolts to the engine. See if it's loose, or the pipe is cracked anywhere. I know what you mean about letting something beat you. It's something simple... it has to be. Maybe a valve is sticking open just long enough to kill the engine, then popping shut so you can re-start it?


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05-18-09, 09:30 PM   #19  
Thanks for the suggestion Indy, I had thought about the flywheel key long ago, & I did pull the flywheel to check it & it looked as new... I torqued the starter clutch to what the manual calls for (I do have the Briggs tool & manuals,, best money ever spent) & adjusted the air gap on the coil to .010, so I'm hoping it hasen't slipped since... It really would only take a few minits to verify that,tho.. Tomorrows project,, I'll let you know... Thanks... Roger

 
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05-18-09, 11:39 PM   #20  
May be sucking air around the primer bulb. Make sure it is not cracked or sucking air in.

 
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05-19-09, 04:54 PM   #21  
I pulled the Flywheel again today & the key looks good... I also checked the intake pipe while I had the fan shroud off & the pipe looks good.. No cracks & it's tight.. I have noticed that there seems to be fuel on the top side of the pump part of the new diagraghm.. Just for a goof I tried another but the same results... When I pull the carb off the tank,,, The little well the Main jet sits in is empty... A few pumps with the primer fills it & It'll run for several mins again.. It won't pump fuel @ a fast enough rate to keep the little well full,,, I have replaced the primer with a new one & cleaned the little ball & seat under it... The primer is the only thing that will pump fuel & I'm thinking it relys on the valves of the fuel pump part to do this?? AmI right??? I'm Stumped again, (STILL!!) Thanks for all the Great help!!! Roger

 
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05-19-09, 05:20 PM   #22  
I think you're on the right track. Is the pickup tube a little loose maybe, allowing air to suck past it when the diaphragm is trying to pump fuel up into the cup? Are the sealing surfaces on the tank where the flaps from the diaphragm seal in good shape and do they have a smooth surface?


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05-20-09, 04:42 PM   #23  
I put the edge of my vernier caliaper along the bottom of the carb & the top of the tank & the best I can tell they are both flat & the ridges are still in the carb.... The Pick-up tube is tight,, @ least I can't turn it by hand... The first carb felt tight too, but I thought it may have leaked & put a bit of epoxy around the stem,,, But that didn't help it,,thats why I'm here with a second carb with the same trouble... Thanks guys,, I appreciate you're patience... Roger

 
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05-20-09, 06:49 PM   #24  
hopkinsr2;
If you will look at the pictures in my previous post you can tell by the change in color of the plastic as to where the carb/diaphram/gasket has failed and let fuel to the outside edges of the carb for a leak. Have a good one. Geo

 
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07-03-09, 10:44 AM   #25  
Hi Guys, I finally had time to re-visit the little briggs & FINALLY got it to run!!! Valve Clearance... The exhaust valve had .003" clearance cold.. Pulled the valves & ground them both ( I'm running .008" both. Little much, but works) & it sounds like the best running little Briggs I'v seen in ages!!! Thanks to all for the help.. All top notch!!! Roger


Last edited by hopkinsr2; 07-03-09 at 10:46 AM. Reason: Missed something
 
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07-03-09, 08:50 PM   #26  
Strange. I've never seen valve clearances let one run fine for 3 or 4 minutes, then shut off. In fact, I don't think I've seen one of those particular little engines even last long enough to need a valve adjustment. Thanks for the update, and maybe it will help any of us who run into this same problem in the future!


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