Briggs & Stratton Engine Problem

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I have a leaf blower that uses a 5 hp B&S "L" head engine. The carb is pretty simple with a choke butterfly, throttle butterfly, and rubber diaphragm fuel pump. The carb sits on top of the fule tank. The carb has no bowl. The governor linakges are clean and the governor appears to be working fine.
The leaf blower was starting to run poorly last fall. This spring it started right up, but after4-5 seconds after running smoothly at proper speed, it will slowly loose rpms and finally stop after 15-20 seconds.
I have cleaned the pick-up tube, replaced the carburetor diaphragm fuel pump along with the gaskets between the carb and the fuel tank, and the gasket between the carb and the engine. I've also disconnected the engine ground wire that normally kills the engine when the throttle is tuned full off. But after doing all this the engine still will not stay running for more than 30 - 40 seconds.
Thanks in advance for any tips, suggestions, or coments.
Manjo
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Got to be spark or fuel, sounds like fuel. Assuming this is a 2- cycle, how's the fuel mix? I always like to check the simplest thing first.
Other than that, you'll have to hold it up to the interweb so I can hear it. -----
- gpsman
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when was the last time you saw a briggs and stratton TWO-CYCLE!?!
s
wrote:

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"S. Barker" wrote:

Although the original poster's engine is a 4 cycle, B&S certainly has made two cycle engines, and I believe they still do, at least for some snow applications.
http://www.briggsandstratton.com/images/bsshop/100/ec_l_800100.jpg
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Well then i stand corrected. I had no idea they'd try that market. I guess they figgered they failed the four stroke test. (they USED to make the best 4 stroke on the market, now they're junk)
s

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gpsman,
Nope, I wish it were. It's a 4-cycle.
I have unlimited web phone. I could call you, but I think I can describe just as well: It starts normally and revs up fine. The governor is NOT NOT pulling the throttle butterfly closed. After 4-5 seconds of running fine, the rpms start to drop and within 10-15 seconds the rpms drop to zero. When it dies, sometimes there's a small puff of exhaust out the carb, and once I could feel a slight spray-back of fuel out of the carb.
Manjo (see other replies below)
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try it with the gas cap off.
s

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s,
I don't think it's a gas tank vacuum problem. I did remove the cap completely and got the same symptoms with no changes (engine ran for a little while then slowly died).
Manjo
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wrote:

Examine the spark plug or just replace it. Check for fuel /air mixture adjustment. Make sure air filter is clean.
Compare sprak plug to this chart.
http://hawkworks.net/sparkplug-chart /
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The old spark plug was installed last fall. But I did replace the spark plug yesterday just in case, but with no improvement.
I'll check the idle screw. There seem to be no other carb fuel adjustment screws per the parts list and B&S repair manual.
Manjo
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Sorry, forgot to reply to additinal tips:
I get the same engine dying with and without the air filter in place.
As for spark plug color, the new spark plug looks a bit oil covered, but I'm guessing the shiny look is more form unburnt gas, but I'm not sure.
Manjo
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Manjo wrote:

Any chance the choke butterfly is oozing closed somehow?
Last year I had a similar frustrating problem with the vertical shaft Tecumseh on my rotary mower. If I pushed down on the handle to raise the front of the mower the engine would slow down noticably, but not stop.
I tried all the usuals, including draining and cleaning the fuel tank and disassembling, cleaning and reassembling the carb with new caskets, etc.
Nothing changed, the engine still slowed down when tilted slightly back. Not wanting to make a PhD thesis out of it I just bought a new carb online, installed it and "Bob's yer uncle", problem gone.
Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat \'57 EE)
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The engine starts, revs properly and then dies with the choke partially or fully OFF about the same time. Keeping the choke on full kills the engine faster.
GROUP REPLY TO Don, Jeff, jp (might be a duplicate post)
A couple of days ago when I started working on this problem, the fuel intake screen at the bottom of the intake tube in the gas tank had a lot of junk in it. I pulled the intake tube off the brass intake tube and sprayed both with non-residue brake cleaner fluid and blew air through the tubes both ways to clean them out.
Yesterday, I DID take the gas tank completely off the engine and used filtered gasoline to flush the tank. I swirled the gas in the tank and then poured the gas from the tank into a funnel lined with a paper filter. The funnel/filter were feeding into a clean gas container. I did this several times and I DID get A LOT more debris out of the tank. Most of the pieces were about 1/64th to 1/32nd of an inch. Some stuff was black and other pieces were sand in color. Im wondering if stuff is getting TEMPORARILY sucked up against the intake screen killing the engine, then the debris drops back on to the bottom of the tank when the engine dies???
There is no fuel line and no inline fuel filter other than the wire screeen at the bottom of the intake tube. The carb fits directly on top of and is bolted to the fuel tank and then the carb is bolted to the engine. There's no fuel line. There's a nylon or plastic feed tube from the carb into the tank. There's also a small reservoir at the top of the tank that looks like a idle feed tube with an intake jet at the bottom that I believe feeds the carb's idle circuit. I blew compressed air through all the carb circuits yesterday, but TODAY I will also spray Berrymans carb cleaner through all the circuits before putting everything back together.
I have the air filter off the carb and can see the entire choke butterfly. The butterfly arm sits in a slotted nylon detent that holds the arm in place. As far as I can tell, the butterfly is staying firmly in place. I don't have a tilting problem since the carb has no carb bowl or float.
I have gotten the engine to run a second or two longer each time I spray engine-starting fuel into the carb intake (at the choke butterfly). But even constantly spraying starter fluid into the carb wont keep it running. I have not tried spraying gas into the carb because I'm assuming the starter fluid is more condensed and more volatile than regular gas.
I hope it is a fuel starvation problem and this will fix the dying problem. If it doesn't, then I'm going to replace the magneto.
Thanks for all the great tips and replies. Please keep them coming if you see I'm missing anything.
Manjo
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Got it all back together and it ran just a bit better. The engine still runs fine for a few seconds and then start the same decline until it stops.
I watched everything and it all seemed to function correctly. I then tried pressing down and twisting the spark plug cap and the engine "seemed" to run a little longer at proper rpm, but it still died. I crimped the spark plug c0onnector and it ran a few seconds more, but still died.
My current theory is there's a magneto or spark plug cable problem. I'm going to try crimping the spark plug cap tighter and if that helps, but doesnt solve the problem, I'll take the magneto off the engine and check it visually.
Does anyone know how to test a magneto? My magneto is behind the pull starter and cover combination, and to gain access to the magneto requires removing the cover, but no way to hand starts the engine with the recoil starter off the engine. Right now, when I do an ohms test, I get 2,500 ohms with one probe on the spark plug cap and the other probe against the magneto body. Does anyone know what voltage the magneto is creating? Can a standard voltmeter be set-up between the spark plug and spark plug cap for a reading, or will the magneto blow out the meter?
TIA for everyone's help.
Manjo
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When you had the carb apart to change the diaphragm and clean the pick- up tube...did you shoot carb cleaner thru the jets to see if they are clear?
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On Apr 18, 6:22 pm, snipped-for-privacy@gmail.com wrote:

My thought on the mag being bad...it would take minutes not seconds for it to thermally fail.
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On Apr 19, 7:59am, snipped-for-privacy@gmail.com wrote:

I don't know anything about magnetos. I have to ask why would it take minutes? Would it take that long for a winding to heat up and separate (if that's possible)? I get a 2,500 ohm reading through the spark plug cap to the body of the magneto. I did visually check the connections and there are only a couple and they seemed in place when I getnly pushed them with a screw driver tip.
Manjo
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Just asking, but isn't WD-40 kerosene?

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You can safely spray WD-40 to run an engine because its propellant is propane gas...and the oil lubricates the upper cylinder. All mechanics know of this...and most use it!
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On Tue, 22 Apr 2008 04:58:18 -0700 (PDT), snipped-for-privacy@gmail.com wrote:

This thread is the first time I've read about using WD-40. Never observed a mechanic use it, but rather they used carb / starting fluid.
Thanks.
(G)
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