Briggs Engine Help

rugaryApril 28, 2013

I have a 12.5 hp Briggs 289707 which had not run for a couple of years. After replacing the starter I put a small amount of gas in the tank and the engine started right up and ran at full engine speed for a few seconds and I then shut it off. I started it again and it ran for a 10 seconds or so and if I recall it stalled. My suspicion was that the gas ran out so I put in a quart or so this time. Now the engine barely idles (very slow and it seems it is missing more than firing). I am also getting what seems to me to be a lot of back pressure through the carb and I also get a bit of a backfire when it dies. Engine speed does not change if the throttle is wide open or when I close the throttle with my finger on the governor (just the sound changes a bit).

I pulled the carb off and cleaned it up as best I could and I also adjusted the intake valve lash (it was a bit tight so I filed it down). Valves were working fine and were moving freely.

Still no change; barely idles with throttle wide open.

I gave it a spray of starter fluid while it was running and nothing happened (actually it stalled out when I sprayed a big dose), no increase in engine speed.

Does the fact that the engine doesn't run any faster with the starter fluid rule out carburetor?

I am thinking ignition, either bad coil or timing is off (flywheel key).

Thing is it ran just fine for the first 20 seconds or so and I did not even try to go anywhere; could the flywheel have jumped???

My bet is coil, anybody seen this before?

Thanks.

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the_0utsider

grab a sheet of paper.
remove the air filter. When the motor is running hold the paper over the air intake. Does the paper bounce or is it just pulled down? Do u see a little "puddle" of gas at the bottom of the intake right before going into the carb?

If bounce\puddle then it is doing what mine have done.
Behind the carb is a plate with a rubber hose in the middle of it. Remove this, turn the motor to top dead center of the compression stroke and measure the gap of the top (intake) valve. Not definite but i think the gap is .05" or .06" the exhaust valve gap is bigger. (just do a search to confirm the gap)

Don't know why but whenever i found those briggs 12hp, they were sitting for a long time. Upon fixing, almost always i would cut my yard fine but this would happen on the second round.

    Bookmark   April 29, 2013 at 12:31AM
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rugary

Outsider, thanks for the reply.

I had already adjusted the intake valve clearence, it was a little tight so I filled it down a bit and got within specs. However, it is still bouncing a piece of paper and I defintely have gas pooling in the intake in front of the carb.

I attributed the back pressure and the pooling gas to the fact that this engine barely run at a slow idle; although it starts quite readily, it will not run any faster than a low idle whether the throttle is closed or wide open.

    Bookmark   April 29, 2013 at 9:32AM
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