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Craftsman LT1000 B&S 16.5Hp Backfiring

12 years ago

My lawn tractor is about 7 years old and the last 3 times I started it, it backfired about 2 of them. It starts up OK after the backfire and runs well after but it has never really done this before. My procedure is to choke it, start it and remove the choke. The last time I started it when it backfired the motor had not been run for a week or so but it was quite hot out (maybe 88F).

Is this a big problem started to happen. Is there anything I can check or do to fix the backfiring.

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Comments (3)

mownie
12 years ago
Thank you for including your "start up procedure" in your post.
Good detail! But I still need to ask: Does the "backfire" sound like a loud blast from the muffler? or is it a more subdued noise like a loud "cough" back through the air intake components? And does the noise occur INSTEAD of the engine starting up (when you first turn the key) or does the noise occur after the engine starts........and when you remove the choke?
If the backfire occurs when you remove the choke, you need to try removing the choke gradually over a period of about 15 or 20 seconds instead of removing it in one rapid stroke.

Cold engines need a very rich fuel mix in order to get started. The choke accomplishes this by depriving the engine of most of the air wanting to rush into the intake when the engine begins turning. Because the choke is blocking the air flow, the mixture of fuel & air entering the engine is at this point "mostly fuel"....and that is what the cold combustion chamber needs to sustain combustion.

Removing the choke before the combustion chamber has warmed (and it warms up in about 30 seconds) enough to sustain the combustion process can cause the mix to become very lean because there is a slight delay in the fuel flow out of the carb increasing to match the increased air flow when the choke is thrown open suddenly.
Unless the engine is showing a lot of power loss under heavy load conditions, there is no reason to think this might be due to the carburetor needing to be cleaned or other reasons.
Try gradually removing the choke and see if the engine behaves.
tomplum
12 years ago
Think back about when the fuel was purchased. If it is over a month and a half old, change it out and see what happens.
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optsyeagle
Original Author
12 years ago
I would say it seems like a loud blast from the muffler but it is difficult to pinpoint since it is unexpected and quick. It is the first thing that happens once I turn the key...bang!. Then I turn it again and it seems to start fine. I stop the choke and it works OK.

The gas is maybe a month old and I use seafoam fuel stabilizer (1% by volume) in every tank. This motor does eat about 1oz of oil for every 1 hr of use. Has been for the last 2 or 3 years. Don't know if that makes any difference. Spark plug, air filter and air cleaner are changed at the end of every season.

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