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Briggs engine running erratically

Discussion in 'Mechanic and Repair' started by DaveT, Aug 13, 2003.

  1. DaveT

    DaveT LawnSite Member
    Messages: 9

    I have an inexpensive Southland 20" mower with a Briggs & Stratton 3.5hp Classic engine, Model 9D902, Type 2213 B1. This past week the engine suddenly started running erratically. It ran in surges. It would slow down to where it would seem to stop then speed up again, then slow down, and so on. It never stopped and it never ran faster than usual. Oddly enough, to me at least, the engine used much more fuel than usual, and, within a few minutes of running out of gas, it would settle down and run properly.
    I had just gotten a can of new gas and suspected possible bad gas or too much ethanol or water in the gas or water in the mower's gas tank. I pulled out the spark plug and it was filthy with built up deposits. I then drained the gas tank and went to work and cleaned out all of the combustion deposits in the combustion chamber--off the cylinder, cylinder head, piston top, and on and around the valves. I replaced the head gasket and spark plug. I cleaned the air filter. I drained the oil and replaced it with fresh oil. I got new gas and filled the tank. The mower ran more erratically than before, almost stopping entirely at times. I let it run for several minutes thinking that there might be some residue of the older gas still in the system, but to no avail. Smoke would blow out of the muffler when the engine surged. I pulled out the brand new spark plug and it was covered with thick black combustion deposits after only a few minutes of use.

    What's wrong? What can I do? I'm not a mechanic, obviously, but I'm fairly handy and not afraid to dive in if the work's not real advanced. If it's something that I should take to the shop to fix, would it be worth it moneywise to spend money on repairs for a cheap mower ($100) or spring for a better one? The mower's only three-years-old and I can't see spending a lot of money on repairing it. About how much would the repairs cost?


  2. That should be the Pulsa-prime carb.
    2 ideas for a fuel problem
    1st - debris in the pick up tube
    2nd - hole in the carb diaphragm, but don't know why it would smooth out at low fuel if that was it.

    You said you cleaned the filter-sometimes they get wet with fuel or water and don't let enough air through causing engine to run too rich. If there is any question I'd start there for $5.

    the plug fouling sounds more like a ring or valve guide problem to be fouling that quickly but hard to tell w/o seeing

    If you need the schematic on that carb let me know and I'll post.
  3. xpnd

    xpnd LawnSite Senior Member
    Messages: 378

    Depending on how much you value your time, you may have already spent more on it than it is worth. A $100.00 mower is designed to wear out--quickly. Prorated over the last three years it cost you $33.00 a year or $1.00 per mowing. I take on projects all the time. A buddy gave me an OLD reel mower that has been sitting outside for the last three years. If you enjoy tinkering with stuff go for it but having a shop fix it will probably cost you at least half of what you paid for it new.
  4. DaveT

    DaveT LawnSite Member
    Messages: 9

    Yes, Bob, please post a schematic on the carb. Funny thing, at least to me, happened yesterday evening. I took off the air filter and housing and started the engine and it ran much better, though a bit rough. I put the filter back on and it still ran better. So, I'm wondering if some debris got in a tube or passageway somewhere and got loose. It still needs some work, though.
  5. Pick up tube

    Attached Files:

  6. diaphram

    Attached Files:

  7. 3rd pic
    these three pics should be enough to remove and clean. There are three pages of info, if you need it e-mail me and I will send all.
    To clean, I take the body of the carb off, set aside diaphram, spay with carb cleaner and blow out with 20-30 psi on air hose.
  8. :dizzy:
    forgot pic

    Attached Files:

  9. DaveT

    DaveT LawnSite Member
    Messages: 9

    Thanks so much, Bob, for the illustrations. They were a big help.

    Well, I did everything -- cleaned up the carburetor and tubes and filters, and springs, etc., replaced the diaphragm, cleaned out the combustion chamber, changed the sparkplug, changed oil -- and the engine was running pretty good. There was some minor, occassional popping, but otherwise it was running well. Yesterday I mowed for the first time since working on the engine. After about 15 minutes, it died. No slow death, no sputtering, no coughing, no wheezing, no backfiring, nothing. It just stopped cold. Nothing I could do could restart it. I took off the air filter, I filled the gas tank to the top, I poured some gas in the carburetor, I sprayed the carburetor with carburetor cleaner, I checked the sparkplug, I let the mower cool down for an hour. Nothing. What should I look at now?
  10. mower_medic

    mower_medic LawnSite Member
    Messages: 77

    A new mower.

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