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Briggs and Stratton 17.5 HP back fires


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05-30-10, 02:01 PM   #1  
Briggs and Stratton 17.5 HP back fires

The Sears lawn tractor was running fine until I went to shut it off. As I was parking it it started backfiring and now won't start. I checked and it has spark, pulled the nut off the fly wheel and could see the key was in place. Checked the valves they looked okay as well as the push rods. Sprayed starting fluid into the cylinder but it still wouldn't start. My compression tester wouldn't fit the spark plug hole so I don't know about the compression although putting my finger over the hole and turning the engine over there didn't seem to be a lot of compression but I could be wrong. It's a Briggs 17.5 model 31c707 type 0230E1

 
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05-30-10, 02:25 PM   #2  
Did you adjust the valves?

 
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05-31-10, 12:28 AM   #3  
If it has compression, try a new spark plug. If it doesn't, put a straw in the spark plug hole and turn the engine by hand to see if the piston is moving.


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05-31-10, 04:19 PM   #4  
No I didn't adjust the valves I didn't think they would have suddenly gone out of adjustment. As far a the straw test I can feel the piston moving up and down.

 
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05-31-10, 11:12 PM   #5  
Then I suggest replacing the spark plug just to eliminate it as a cause. If no go, remove the valve cover and look at the valves/rocker arms...you may have a stuck valve.


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06-01-10, 05:38 AM   #6  
i just rebuilt 31c707 i would chk the valve adjustment and check the key in fly wheel agin by removing the wheel

the speck on the valves are
.003 -.005 on intake
.005-.007 on ex
and you want to adjust the valves after top dead center about 1/4" down from tdc
flywheel 65 foot pounds (if you don't tork to speck you will be replaceing the key)

 
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06-03-10, 04:54 AM   #7  
I tried a new plug but it still wouldn't spark. I looked at the valves and they seemed tyo be working at least the push rods were moving. Is there anything else that would cause it top back fire and not start? As mentioned earlier it was working fine until I parked it and turned it turned the gas down that's when it started back firing and then wouldn't start.

 
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06-03-10, 06:21 AM   #8  
maybe you'll need to check the flywheel key

 
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06-04-10, 05:16 AM   #9  
I pulled the nut off and the key was in place. I didn't remove the flywheel because I could see the key in it's slot.

 
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06-04-10, 06:02 AM   #10  
Have you checked the fuel solenoid on the bottom of the carb?

 
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06-05-10, 05:49 AM   #11  
No but it is getting gas to the carb. Is there a way to check the solenoid?

 
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06-05-10, 05:58 AM   #12  
You should be able to hear and feel it click when you turn the key to Run. Best to remove it and verify the plunger pulls down as well.

 
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06-05-10, 02:49 PM   #13  
There is no clicking sound. I tried to pull the electrical connection apart but it didn't want to separate. Is there anything special or should I just pull it harder? What does this solenoid do? When I shot either into the air filter and spark plug hole it still wouldn't fire. One other observation it turns over when I'm not sitting on the seat should this happen? I know it shuts off when you get off the seat.

 
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06-06-10, 04:05 AM   #14  
Check to be sure all your safety switches are working properly. If you tried to start it with either and nothing, are you sure you have spark? Pull the plug and check. A bad safety switch will cause loss of spark. I spent several hours on a John Deere with no spark to discover that the neutral safety switch was bad. Good luck!

 
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06-06-10, 05:40 AM   #15  
It has spark, I had someone sit on the seat and turn it over as I checked

 
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06-13-10, 05:24 AM   #16  
Did the owner ever get this straightened out. I had a similar situation about a month ago along with what appeared to be a bad cam. Same backfire scenario -- key was in place, would not start, fuel solenoid working.

 
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06-17-10, 04:52 AM   #17  
No I never got it straightened out. It's sitting under a tarp I ended up buying a new Cub Cadet.

 
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06-17-10, 05:12 AM   #18  
Thank you for the reply -- I am sorry you could not straighten it out.

 
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06-18-10, 04:40 AM   #19  
If you get yours running please post your answer.

 
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06-18-10, 05:17 AM   #20  
This was a customer unit and the customer decided to purchase a new unit. I am in the process of trying to purchase it. If I can buy it and get it running, I will post the info.

 
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06-01-11, 06:01 PM   #21  
i have a ten year old sears tractor with the 17hp briggs.
the mower hasnt been used much at all over the years.
today while mowing, all the sudden the engine started running rough and losing power.
i determined the engine is backfiring on every stroke. if i run the engine with the air filter off, it sounds like firecrackers.
i unbolted the carb and just cranked the motor, and could hear what sounded like air rushing back out through the intake valve. i'm guessing the intake valve is sticking or cam is messed up.

 
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06-01-11, 08:37 PM   #22  
Posted By: searstractor i have a ten year old sears tractor with the 17hp briggs.
the mower hasnt been used much at all over the years.
today while mowing, all the sudden the engine started running rough and losing power.
i determined the engine is backfiring on every stroke. if i run the engine with the air filter off, it sounds like firecrackers.
i unbolted the carb and just cranked the motor, and could hear what sounded like air rushing back out through the intake valve. i'm guessing the intake valve is sticking or cam is messed up.
any oil in the air cleaner, could be head gasket if it's OHV .

 
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06-02-11, 04:38 AM   #23  
Posted By: mgmine If you get yours running please post your answer.
I was able to buy the tractor. The problem was a stuck intake valve causing the backfire. There was a lot of carbon buildup around the top of the valve causing it not to close completely. It also needed a new starter. It runs fine now.

 
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06-02-11, 10:31 PM   #24  
Posted By: 38racing any oil in the air cleaner, could be head gasket if it's OHV .
very little....probably from the crankcase recirculation tube.
i unbolted the carb, and the intake chamber looked very dry.
i may have to look at the valves and head.

 
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06-05-11, 04:47 PM   #25  
ok, took valve cover off and found the intake rocker stud had backed out. tightened it up and she ran good. i'm thinking of putting some red loctite on the threads. good idea?

 
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06-05-11, 06:04 PM   #26  
Yep, good idea, just make sure you clean all oil residue from the stud and the hole. Carb or brake cleaner works well.


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04-29-12, 07:50 AM   #27  
broke intake rocker arm

i have a 2004 pony troybilt mower with a 17.5 briggs and sratton motor was running fine until other day i went to crank it and the intake rocker arm broke, could this be from a stuck intake valve or out of timing?

 
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04-29-12, 10:32 AM   #28  
It could be from a stuck valve, but you can check that by simply pushing both valves in and see if they each travel about the same amount. It might have just been a malfunction.


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