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Discussion Starter · #1 ·
I have a briggs 650 series that is backfiring through the exhaust and not idling smoothly. The engine has very low hours. The fuel and carb are clean, the flywheel key was ok and I replaced it as a precaution. The engine also backfires at higher RPM's but not as bad as at idle. The odd thing is (for me), is that the engine always starts on the first pull.:help:
 

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Is there a possibility the fuel in it could be stale?

Another thing to check for is to confirm the choke is disengaging properly.
 

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Discussion Starter · #3 ·
650

The fuel is fresh, though 10% ethanol. I'll have a look at the choke, thanks. I mowed with it today, plenty of power but rough.
 

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I forgot to mention this in my first post, but another possibility could also be the float sticking in the carburetor as well.

It sounds like it's getting flooded with fuel which makes me think it's the choke that's partially closed or the float that's sticking.
 

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Discussion Starter · #5 ·
My 650

Thanks for the tip! I know what I will be doing this afternoon. Cold and rainy here in Bavaria, good day to hide in the garage.
 

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Discussion Starter · #6 ·
My 650

Ok, the d*mn thing still backfires! Here is what has been tried:
Gas is fresh, plug is new, flywheel key has been changed, carb is clean (no choke, just a primer bulb), swapped the coil, carb is tight on flange, no oil or fuel leaks. Engine is two years old, I changed the flywheel back then, from light to heavy. Flywheel was direct from B&S.:mad:
 

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Discussion Starter · #7 ·
My 650

Ok, now that I ranted a bit I can go back to thinking logically about the matter. Still, I am facing a brick wall.:dunno:
 

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... I changed the flywheel back then, from light to heavy. Flywheel was direct from B&S.:mad:
It worked ok after changing the flywheel, correct?

About the only thing left I can think of would be the valves, namely a problem with the exhaust valve or valve spring.

Here's a link to the Briggs FAQ about backfire and afterfire:

http://www.briggsandstratton.com/support/frequently-asked-questions/Backfire-Antifire%20from%20carburetor%20or%20muffler/?body_0$tbKeyword=backfire
 

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Discussion Starter · #9 ·
My 650

Thanks for replying, Mark! Yes, after the flywheel change everything was ok. I noticed that when running, the butterfly on the carb is moving back and forth the whole time when at idle...as if the governor is pushing/pulling rapidly the whole time.:dunno:
 

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.. I noticed that when running, the butterfly on the carb is moving back and forth the whole time when at idle...as if the governor is pushing/pulling rapidly the whole time.:dunno:
What happens if you hold the throttle plate from wiggling? Will it smooth out?
 

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Discussion Starter · #12 ·
My 650

Ok, here is where I am. I pulled the cylinder head and crankcase breather. The head was slightly oily, the breather was very oily at the bottom. I don't see any obvious damage to the valves. This engine is a bit less than two years old and has been very well cared for.:dunno:
 

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Ditto. :dunno:

Did you by chance ever hit anything with the blade hard enough that it could have bent the crankshaft?

I was actually surprised to hear that swapping the coil, plug and shear key did not cure it. Those would have been my strongest bets. :confused:
 

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Discussion Starter · #14 ·
My 650

Hello Mark! I am taking the weekend off from my Briggs. I need to do this before I throw it into the Donau (Danube) down the road from me. I never hit any object larger a twig,the crank can not be bent. I cleaned the carb again and check the valve lash. I also have a new head gasket I will try out. Who knows, maybe it healed itself.:ROFL
 

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Discussion Starter · #15 ·
650 self-healing engine

I am at a loss for words on this one. I left my 650 in the corner of my shop for over a week under an old sheet. I then put everything back together as before and the d*mn thing runs as it should, smooth with no backfiring. Don't get me wrong, I am overjoyed that everything is as it should be. I am just puzzled at this. Briggs makes me crazy. They used to make great small engines over here in Germany. They were simple and almost indestructible (look up Berning DK-6). The companies here could not crank them out in the numbers that Briggs did or as cheaply. As is the case in many industries, cheap won out over quality.:soap:
 

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Hello, there, Hooks. Great to hear that your motor fixed itself! In addition to what you have done, for future preventative maintenance, I would suggest adding just a small amount of carburetor cleaner to your gas. Something along the lines of SeaFoam or similar. Just to keep things clean and open in the passageways.

Hope to see you on the forum regularly. After your problems with this engine, you are now well versed in various troubleshooting processes!
 

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I am at a loss for words on this one. I left my 650 in the corner of my shop for over a week under an old sheet. I then put everything back together as before and the d*mn thing runs as it should, smooth with no backfiring.
The bed rest with the sheet must have done the trick. :ROFL

Briggs makes me crazy. They used to make great small engines over here in Germany. They were simple and almost indestructible (look up Berning DK-6). The companies here could not crank them out in the numbers that Briggs did or as cheaply. As is the case in many industries, cheap won out over quality.:soap:
Unfortunately we are seeing the same thing happening over here with a bit of a twist. Briggs for many years also used to make a great little engine here that would run for many years and put up with a lot of abuse. Anymore not so much. We lost Tecumseh, Briggs and I would also add Kohler are scrambling and have cheapened up the designs on all but the high end models. (I question at times if the high end models are not starting to suffer as well.) The Chinese have now firmly worked their cheaper engines into the lower horsepower lawnmower, tiller, snow blower, and generator market here. I figure it is only a matter of time before they start showing up in riding mowers and tractors. Quality of them seems really hit and miss. One guy reports he has over a 1000 hrs on one with no problems. Next guy reports he's draining the leftover from machining metal shavings out of the sump on the first oil change. :dunno:
 

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Discussion Starter · #18 ·
650

I will be sure to do that with the carb cleaner and gas. I also always fun the tank and carb dry in Fall. I have also stopped using ethanol fuel in my Briggs and and Honda. I am sure it ruins these small engines in the long run. It is hard to feel sorry for Briggs the corporation, this is the same thing they did to crush all of the smaller manufacturers since the 1950's. The ones I feel sorry for are the American workers, fearing the loss of yet another industry, again only through greed and the obsession of (most) consumers to have the prices constantly go down without seeing the true cost. It reminds me of a bumper-sticker I saw many years ago: "Hungry? out of work? Eat your foreign car!". Ok, I'll hop down off the soap box and do something productive. Machts güt, meine Freunde!
 
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