QuestionQUESTION: this is a 2001 model & it has a new spark plug. The oil has been changed regularly & the air filter has been serviced. It seems to start backfiring after it warms up, & loses speed & maybe power. I am wondering if it could be the fuel & if it is, how can I get around it if all the fuel I buy has ethanol. Thanks in advance for any help.
ANSWER: Is it backfiring through the carburetor or the exhaust?
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QUESTION: I believe it is through the carburetor. If it matters the model number on the valve cover is 446777.
AnswerThere are two likely possiblities. One is that the carburetor needs to be gone through as it may be running too lean. The other is that you have a valve not closing.
If it's the carburetor, you may be able to improve it with spray cleaner. I'd try that first, but wouldn't be surprised if it doesn't help. The kit for your carb runs around $30 so it's worth a shot. If it doesn't help, then I'd go ahead with the carb rebuild. You'll need to soak it for an hour or more in carb cleaner and chase all the holes with some fine wire.
If you have a valve problem, the easiest way to diagnose it is with a leakdown test. Most shops can do this. We charge $50 on twins, which is about average I think. Some of the Briggs engines have valve seat problems, hopefully this isn't the case with yours.
Ethanol blended fuel is a lot of trouble, but it doesn't really cause problems with operation. It causes all it's troubles by having a very short shelf-life and by absorbing water from the air at a very fas rate. It also evaporates quickly, leaving behind dirt and varnish. Hopefully all that's happened with yours is that you have a gummed up carb from that action. We now use SeaFoam or Techron in all the gas cans in the shop and recommend all our commercial cutters do the same. I think it's a good idea for residential mowers too as they tend to sit unused for longer periods of time. Thanks, PK.
