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17hp Briggs revving up and down and Backfiring


nyptukdoc's Avatar
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09-02-09, 02:24 PM   #1  
17hp Briggs revving up and down and Backfiring

I'm back with another issue with my Briggs 17 HP (Mod.#42A707, Type 2653E1) on a Murray Select 42" mower. Last month I cleaned the carb and needle valve due to gas getting into the oil.
Now it cranks right up but when I have the throttle in the slow(turtle) position the engine revs up and down constantly. It sounds like it is about to quit, then it revs back up. If I move the throttle to fast it smooths out. When I turn the mower off, it backfires. Any ideas on what is going on.

 
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09-02-09, 03:03 PM   #2  
The rest of the carb needs cleaned and serviced. Most times "surging" is caused by a fuel restriction.
If you cleaned trash from the needle valve then it is very likely some trash got past and is now clogging other jets and or ports in the carb.

 
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09-02-09, 05:40 PM   #3  
When you cleaned the carb the first time did you clean the fuel tank and flush the fuel line along with replacing the fuel filter ?

 
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09-02-09, 06:06 PM   #4  
I did not clean the tank, flush the lines nor change the filter. I will break the carb down re-clean it and do the other stuff you guys suggested tomorrow. Could these things also be what causes the backfire when I turn the engine off?
I'll post my results when I finish.

 
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09-02-09, 06:20 PM   #5  
Posted By: nyptukdoc Could these things also be what causes the backfire when I turn the engine off?
It's very possible, Perform as stated and see how it does, If it still backfires shout back.


Good Luck

 
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09-03-09, 12:59 AM   #6  
Still something in the carb. Did you remove the main jet and clean it out and the area behind it (it is accessible through the drain plug opening)? Does it have a mixture screw on it in front under the bowl area? If so, try backing it out 1/4 to 1/2 turn.


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

God bless!

 
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09-03-09, 09:04 PM   #7  
I did not remove the main jet and clean that area on the first carb cleaning.
Also, in the area you describe, the carb does have what the owners manual calls a "non-adjsutable idle mixture jet". Should I back that out a 1/4 to 1/2 turn?

 
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09-04-09, 12:07 AM   #8  
No, but you can unscrew it and clean it out as well.


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

God bless!

 
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09-04-09, 09:27 PM   #9  
I'm back running smooth!!!
I cleaned everything up and it works fine. No more surging and it did not backfire.
My number one culprit was the main jet. When I removed it, I could see a small piece of gunk hanging out of the end.
Once again great call and excellent advice!
Thanks guys.

 
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