Craftsman

20 up Briggs & str. New motor started running rough. Changed fuel.
Experienced gardeners share their insights in answering this question :
It sounds like the valves are out of adjustment.

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Low fuel pressure can cause a backfire when there`s too much air and not enough fuel in the combustion chamber. This can be rectified on lawn mowers with speed settings by simply increasing the speed and thus increasing the fuel supply. Another possible cause is a failing fuel pump or even an old fuel filter.
The primary cause of a backfire is decelerating too quickly. The simple fix for this is just to lower the engine speed a bit more gradually. If you have a throttle that you use to reduce speed, gradually let it up instead of letting it rebound quickly.
The spark inside the chamber may not burn up all the fuel, allowing a little extra gasoline vapor to enter the exhaust, and lead to a backfire. This can be caused by a faulty mass airflow sensor or a clogged engine air filter “choking” the engine and not allowing enough oxygen to flow into it.
One of the most common causes is a stuck or faulty air intake or gulp valve near the exhaust manifold. Backfiring can also occur with a sudden drop in fuel pressure. This may be due to a faulty fuel pump or a plugged fuel filter. Correcting problems in the fuel system usually resolves these issues.
One of the most common causes of a sputtering engine is an issue with the vehicle`s fuel system—the filter, pump, and injectors. These three critical components work together to ensure fuel flows smoothly from the fuel tank to your engine`s fuel injectors, and then pumps into the engine evenly.
Note: Backfire and afterfire through the carburetor will not harm the engine at all!
Assuming all of your plugs and wires are in the correct locations and you haven`t messed with the timing at all, then the most common cause of backfiring through the carb (spitting or coughing) is in the morning when a carb`s air/fuel mixture is a bit too lean. This usually goes away once the engine warms-up.
You Lose Power in the Middle of Mowing:

Here`s why this happens and what you can do: Dirty Air Filter on Your Lawn Mower: Clean or replace. Dirty Spark Plug: Clean or replace. Build Up of Clippings & Debris: Clean underside of your lawn mower deck as noted above.

Loose, Dirty or Disconnected Spark Plug in Your Lawn Mower: Check it out, clean off debris, re-connect and tighten. Dirty Air Filter: Clean or replace. Fuel Not Reaching the Engine: Tap the side of the carburetor to help the flow of gas. If this doesn`t work, you might need a new fuel filter.
Backfires and afterfires are worth paying attention to since they can cause engine damage, power loss, and decreased fuel efficiency. There`s a variety of factors that can cause your car to backfire, but the most common ones are having a poor air to fuel ratio, a misfiring spark plug, or good old-fashioned bad timing.

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I started my craftsman 21hp 42in deck today it had a rough idle with backfire and when engade mower it seemed to not have enough power
ANSWER : Backfiring is a sign of too rich on gas and not enough air. Not enough gas will cause the mower to bog down when blades are engaged as it isn’t powerful enough to run the motor AND turn the blades. Check your carb and see if you need to clean it and replace diaphgram. Sounds a lot like a carb problem.

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Craftsman riding mower lt-1000 leaks gas – Craftsman 17.5 hp 42 in. Deck Lawn Tractor – CA Model
ANSWER : Need to fix that. it may be a fire hazard.

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12.5 hp craftsman runs fine for only the first 1/2 hour or so
ANSWER : You are so right, the coil has a small crack the opens up as it heats up. You know the old saying as metal heats it expands this causes a open circuit.

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I have a 1987 craftsman riding 17 horse mower. I
ANSWER : Smoke is fine as long as you keep adding oil!!! Rings are worn,,,

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Craftsman riding mower loose belts need tighting
ANSWER : Http://www.disruptit.com/manuals/L0403195.pdf

Here ya go.

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Starts and runs fine for a short time backfires and runs very rou
ANSWER : More info

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What type of oil for 17.5 42 500 cc – Craftsman 17.5 hp 42 in. Deck Lawn Tractor – CA Model
ANSWER : I use straight 30wt.

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Lawn mower cranck but wont start…
ANSWER : Since you already checked for spark and air I would drain all the fuel out of it and check that fuel for water. Over time some lawn mowers end up with contaminated fuel. You can see the water sitting on the bottom of the fuel if you let it stand for a bit in a small plastic bowl.

Be sure to empty and dry out you fuel can as well. Especially if the mower stopped running right after a refuel. Which is a good sign your gas can is contaminated too.

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