Briggs & Stratton Rough Idle & Backfire

Model 28N707-1036-E1 Briggs & Stratton Cast Iron Cylinder. Backfire through exhaust, and rough idle. Acts like it wants to stall at low idle.

Rebuilt and painted the engine, cleaned piston, rings, grooves, and head (Gaps Were Good) rebuilt the carb with a kit & cleaned thoroughly. All new gaskets, and seals. New air, fuel filter, and fuel line. Cam, lobes, and crank looked good. Triple checked timing marks. Checked compression release, and that was good. I also took the flywheel off again, to check the key and that checked out just fine. (I’m stumped)!

Gaps are
.30 for spark plug
.003 for intake
.005 for exhaust

Just received the new B&S magneto, and plug, going to install that Monday. 7/8/13. I will post updates.

(Update) The problem was the Magneto. Runs like new now!

(Click on the link below to find a Briggs dealer in your area. Most of them will only charge $30 bucks to come out and do a good tuneup)

Any help, or advice would be appreciated.



29 thoughts on “Briggs & Stratton Rough Idle & Backfire

  1. Update 7/12/13 Turns out it was the MAGNETO! It runs beautiful now! Now I just got to get my low speed, and mixture tuned right. At full throttle it wants to go to 3600-3650RPM I think this is because I adjusted the governor before assembly. I might call a briggs tech out. They only charge $30.00 to come out for a house call tuneup. I just wanted to say I really appreciate your time, and all your help. Thanks so much George! Have a blessed day!

  2. I had the same problem with a Honda HRU196 lawn mower,it was caused by an air leak between the carby & the inlet port on the cylinder head,so I made some gaskets up for it & it runs fine now !!!!
    I've got another push mower with other problems, it is hard to start,blows a fair bit of smoke when cold & Lacks power,its got a 1988 B&S motor on it which has a compression pressure of 97 PSI dry & 120 PSI on a wet test,so the piston rings are worn & need replacing !!!!

  3. I have the same problem when I try to rev it up to high throttle it does not want to run right seems like it's surging and little backfire out of the carburetor please help was this problem ever solved on this kids video oh one more thing it will run find at low throttle but soon as I raise the throttle she starts surging

  4. I just did an oil change. I used an inch short oil filter. rode in down the rode.. had on 6 speed. turn throttle down and it shut off.. tried to turn on later and it back fires every second. I'm a rookie can anyone help

  5. Just got the flywheel keys, and metal flywheel gear in yesterday. Have had major storm weather for over a week. Hope to get everything installed this weekend. Will keep updates!

  6. I will replace the magneto, and plug Monday, and hopefully that will clear it up. I am going to replace the fuel to just to make sure. I added some dry gas but that didn't help at all. Really appreciate your time, and help.

  7. Let me know how things do after the new plug and magneto are installed with some fresh gas.. I have rebuilt many briggs engines as well as modified them to run on ethanol for gokart applications, I'm sure we can figure something out. Double check that choke tho.

  8. Alot of folks mistake a spark with "good spark".. Removing the plug and spinning the engine over to visibly see a spark is a good way to ensure its there, but quality of the spark is a far different element. Weak spark is very misleading in that: the owner thinks because it's present means its good… Not always the case and weak spark can also cause the condition you are experiencing.

  9. Appreciate the help. This video is the engine after I just rebuilt it. I rebuilt the carb, cleaned piston, and rings. Gaps were good. I just ordered a new B&S plug to make sure it didn't foul out. I am going to replace the fuel as well to make sure that was not the issue. Spark Plug gap is .30, and for the valves .003 for intake gap, and .005 for exhaust gap.

    I also am trying a new magneto, as the old one had a contact that came loose, and wouldn't start unless I bent it to contact the magneto.

  10. If your engine was stored over the winter, with fuel in the carb bowl, there is a high possibility it is gummed up. a simple carburetor cleaning can remedy this, but in some cases a rebuild is warranted. Secondly if your choke is gummed up and not opening properly, it will give the engine too much gas and not enough air, sending un-burnt fuel into the exhaust, at which point it will ignite "post cycle" and create an exhaust backfire

  11. Your engine appears to be fairly new. A backfire out of the exhaust could be a few simple things.. Gas quality: I would recommend draining the tank and ensuring quality fuel is present. Spark Quality: check the spark plug gap and ensure good spark.. Air filter quality: make sure the engine can breath.. then once the above are eliminated you can move on to more complex diagnosis.. With what little info we have to go on at this point, it acts like Carb/fuel/choke issues tho.

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