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Tractor Talk Discussion Forum

Briggs 11 hp won't run

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Jerry Seilhamer

04-27-2004 12:19:44




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Last fall I was using my tractor and it was running fine. While it was just sitting at an idle, it started backfiring through the carb and then shut off. I haven't been able to start it since. I checked the compression, tore apart the carb and blew out all the ports, checked the flywheel key, cleaned and gapped the points and even pulled the head to look at the valves. I can't find anything wrong but it will only backfire through the carb and refuses to start. Anyone got an idea?

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Is It running yet!!!!

05-02-2004 16:06:37




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 Re: Briggs 11 hp won't run in reply to Jerry Seilhamer, 04-27-2004 12:19:44  
I sent you an email to see if you have it running,still no answer, would you let me know how you made out Thanks



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Jerry Seilhamer

05-03-2004 04:24:28




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 Re: Re: Briggs 11 hp won't run in reply to Is It running yet!!!!, 05-02-2004 16:06:37  
Well after rechecking everything and finding nothing really wrong, I decided to try another new spark plug. Wam bam it fired off in less then one rotation of the flywheel. Go figure. Runs like a champ again.



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Clary

04-29-2004 05:49:03




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 Re: Briggs 11 hp won't run in reply to Jerry Seilhamer, 04-27-2004 12:19:44  
I work on small engines all of the time & know for a fact that you have to have fuel, Compression and a spark to get things running plus everything has to happen at the right time. 1st run a compression test - It needs to be around 125 psi - You say you checked the flywheel key - Was it just a visual inspection w/o pulling the flywheel? If so the flywheel has to come off because the key can be sheared even the smallest amount & cause the ignition to be out of time.
Is this an eng.w/points or electronic ignition made onto the coil? If it is electronic it will fire even w/a sheared key. My bet is that the intake valve is not seating off & causing the blow back thru the carburetor.
The valve will need to come out & the valve face & seat will need to be cleaned then laped in & the valve face may also ne to be refaced in a machine shop then lapped in w/lapping compound.
If you do this then check the valve clearence between the valve stem & lifter - W/the engine on the compression stroke & piston @ top dead center and both valves closed it should be around .011 thousandths. Try this and let me know if things work out

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Nor. Al

04-28-2004 05:31:17




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 Re: Briggs 11 hp won't run in reply to Jerry Seilhamer, 04-27-2004 12:19:44  
Jerry I had one that didn't have points or condenser it had the electronic coil on top of the flywheel. Mine did the same way and it had a bad flywheel key, if thats not the problem then its a bad valve. I would try a new flywheel key 1st. good luck



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Robert

04-27-2004 15:58:50




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 Re: Briggs 11 hp won't run in reply to Jerry Seilhamer, 04-27-2004 12:19:44  
I have some limited experience with Briggs, and, it sounds as if your problem is fuel related. You said it was running, then quit, now only backfires through the carburetor. With that information, if it were mine, I'd begin by carefully pulling the carburetor, dismantiling, then try to see what the fuel level is in the bowl. While there, I'd check to make sure the float hasn't developed a pin hole, allowing it to become "heavy", thereby not shutting fuel off---essentially flooding the engine. Depending on the type carburetor you have, there's probably a mixture adjustment screw. On my 8 hp Briggs, there's a nozzle located beneath the screw---you have to remove the screw, then screw out the nozzle, to clean passages.
There's also a fuel "pump" of sorts on these things, that works off the valve pulses somehow, and to find if there's a problem in this area, look to where the rubber tube goes (I'm talking about the tube that's on the air cleaner)follow the routing, and take the cover off, make sure the little diaphragm isn't cracked, or has trash behind it.
I don't think your problem is major, just frustrating. The fuel is most likely okay. I haven't found fuel to deteriorate over the course of a winter, but it would be easy enough to drain and refill. I hope this is of some help. Good luck!

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Red Tail Hawk

04-27-2004 15:45:50




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 Re: Briggs 11 hp won't run in reply to Jerry Seilhamer, 04-27-2004 12:19:44  
When an engine back fires thru the carb, 9 times out of ten your timeing is off. I know what you have told us but if it is still not running go out buy a new key and replace the old one. My rototiller use to drive me nuts.Please keep us posted before I go any deeper. Good Luck



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Dick2

04-27-2004 15:35:49




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 Re: Briggs 11 hp won't run in reply to Jerry Seilhamer, 04-27-2004 12:19:44  
It's a Briggs: they weren't really meant to run very long anyway.



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Dan

04-27-2004 15:35:19




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 Re: Briggs 11 hp won't run in reply to Jerry Seilhamer, 04-27-2004 12:19:44  
Long shot but are you sure your fuel line does not have a hair line crack and is sucking air by the off chance.



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pasbon

04-27-2004 13:04:09




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 Re: Briggs 11 hp won't run in reply to Jerry Seilhamer, 04-27-2004 12:19:44  
you might check the gap between the lifter and the valves , they have a tendency to close that gap and cause it to pop back. just a thought...



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Hal/WA

04-27-2004 22:19:56




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 Re: Re: Briggs 11 hp won't run in reply to pasbon, 04-27-2004 13:04:09  
I have also had the gap on the intake valve become too tight or non-existant and the symptoms my engine had were hard starting and spitting back through the carb while the engine was being cranked. When I dug into the engine, I found that the intake valve was not making a good seal on the seat when the valve was at the lowered position.

I removed the intake valve and ground a small amount off the end of the stem. I also hand lapped the valve to the seat with valve grinding compound. Before I put it all back together, I verified that the clearance between the valve stem and lifter was within specifications. The engine then would start and run fairly well and I used it another year.

For awhile before I was forced to do the repair because it just wouldn't start anymore, the engine could be started with ether, and once it was running, ran OK. I suspect that over time the valve and seat wear, causing the valve to be further into the engine block and reducing the clearance between the stem and lifter. I did compression tests as part of my diagnosis and did not get extremely low readings like I would have expected from a burned valve or bad rings. Confusing.....

I suspect that the leaking intake valve caused a totally wrong mixture for the engine to start, with the air leaking back into the carb/intake manifold, and that was why the engine would start for awhile with ether, until the leaking valve got too bad.

Good luck!

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Hal/WA

04-28-2004 22:48:04




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 Re: Re: Re: Briggs 11 hp won't run in reply to Hal/WA, 04-27-2004 22:19:56  
I thought a little more about this. Since the engine was running fine, but then started spitting back thru the carb, I would suspect that some carbon or other gook is holding the intake valve open a little bit. I would pull the head and try blowing into the carb by sealing the air intake with my lips when the intake valve looks closed. If the carb/intake will not hold pressure and is leaking around the valve, the problem would be found. I suppose a valve could also get bent somehow, but I really don't know how on a flathead??

I had a real hard time getting the flywheel off my engine. 20+ years makes parts bond to eachother pretty well. I had suspected a sheared key, but it was fine. I could see why an engine would not run if the ignition timing is wrong, but don't see how wrong ignition timing would make an engine spit back through the carb. But I sure could be wrong.....

Always lots to learn!

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Allan

04-27-2004 12:42:00




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 Re: Briggs 11 hp won't run in reply to Jerry Seilhamer, 04-27-2004 12:19:44  
Jerry,

While you had the head off, did you inspect the valve seats? They have a nasty habit of coming loose.

Just a thought,

Allan



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Jerry Seilhamer

04-27-2004 12:47:17




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 Re: Re: Briggs 11 hp won't run in reply to Allan, 04-27-2004 12:42:00  
I looked at them and they appeared to be tight.



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bo

04-27-2004 12:22:03




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 Re: Briggs 11 hp won't run in reply to Jerry Seilhamer, 04-27-2004 12:19:44  
Didja try a tablespoon of gas straight into the cylinder to see if it attempts to start?



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bo

04-27-2004 12:23:13




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 Re: Re: Briggs 11 hp won't run in reply to bo, 04-27-2004 12:22:03  
You also didn't say it had spark...does it?



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Jerry Seilhamer

04-27-2004 12:29:55




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 Re: Re: Re: Briggs 11 hp won't run in reply to bo, 04-27-2004 12:23:13  
Yes it has spark and it gets gas because it will puddle up in the bottom of the carb if you choke it too much.



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don

04-27-2004 15:41:42




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 Re: Re: Re: Re: Briggs 11 hp won't run in reply to Jerry Seilhamer, 04-27-2004 12:29:55  
Maybe I can be a little bit of help and I'm not much on single cylinder engines my field is diesels but my son just had this problem last week and I was checking to see if he sheared a flywheel key because he said when he hit something with his blade it killed the engine and he couldn't start it again so naturally I checked his soft flywheel key and it was ok but I noticed the gap on his relucter was very wide so I repositioned it closer to the flywheel and it took off and ran ok I really don't know what the gap is for it but I'm sure you can find out from one of your local Briggs dealers or the Briggs website. One thing is make sure you have new gas in the tank with this new gas it does not hold up well over the winter unless you use Stabill because it sounds like you have everything you need to make an infernal combustion engine run especially when you have plenty of gas running out the intake it should at least act like it is choked which is an air mix adjustment which is the screw underneath the air cleaner.Good Luck, Don

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