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Help! 12 hp Briggs stalling problem

Discussion in 'Mechanic and Repair' started by EX20, Jun 20, 2006.

  1. EX20

    EX20 LawnSite Member
    Messages: 7

    I have a 93' Murray rider with a Briggs 12hp motor.
    Model 284707, Type 0135 01, Code 9505154E.
    It has a Walbro carb, 5-4993.
    When cold it always starts up and runs great. After 15-20 min of cutting it starts sputtering and dies, I can start it choked but it runs bad and dies again. If I wait 15 min it starts up and runs great until the same thing happens again. Multiple plugs have been tried (Champion and NGK), Got into the valves and ground off a few thousandths off the valve stems to make sure I had proper clearance between the lifters to valve stem (both valves) for when the motor reached operating temp. Carb looked very clean. Sanded down the carb flange on a tabletop with sandpaper. In case there was some warping of the carb flange where it bolts to the intake elbow. Nothing fixes it. Any ideas?
  2. EX20

    EX20 LawnSite Member
    Messages: 7

    Oh, and I also need to know how many turns out the jet should be on the body of the carb. 1.5 turns, 2.5 turns?
  3. khouse

    khouse LawnSite Bronze Member
    Messages: 1,465

    it could be as simple as a non working (venting) fuel cap or fuel filter plugged.
  4. Restrorob

    Restrorob LawnSite Fanatic
    Messages: 11,029

    When it sputters to a stop check for spark, The coil could be heating up and failing.
  5. EX20

    EX20 LawnSite Member
    Messages: 7

    I forgot to mention that I checked the vent in the fuel cap. It's open. Inline filter is clean. I was suspecting the coil too, but I was under the impression that they rarely, if ever failed. I'll try checking for spark when it starts stalling.

    Thanks for the replies.
  6. EX20

    EX20 LawnSite Member
    Messages: 7

    On the issue of how many turns out the jet should be, any advise?
  7. Restrorob

    Restrorob LawnSite Fanatic
    Messages: 11,029

    That adjuster is for the low speed, The high speed is fixed. Start at 1 1/2 turns, Start the engine and let it warm up if it doesn't quit before then and set the throttle at idle. Turn the adjuster in 1/4 turn at a time until it starts to idle slower then back it back out until it starts to lower then split the difference.
  8. mike lane lawn care

    mike lane lawn care LawnSite Bronze Member
    Messages: 1,707

    i have this SAME problem and same engine and same tractor. it runs but when you put it into drive it just dies.
  9. Restrorob

    Restrorob LawnSite Fanatic
    Messages: 11,029

    I don't think you have the same problem because EX20's runs for 15/20 mins., Your's sounds like a safety switch problem. Possibly seat or PTO.
  10. EX20

    EX20 LawnSite Member
    Messages: 7

    Ok , did more troubleshooting.

    Idle is set. It ran again tonight for awhile. Seemed to run longer. About 10 degrees cooler than last night. 70deg. vs. 80+ yesterday. I don't know if that matters.

    As soon as it died I pulled the spark plug and it had spark. I also pulled it away from the engine while cranking and it had a 3/8"+ long spark from the ground strap of the plug to the engine, until I pulled too far away and it zapped me. That was fun........twice.

    I also discovered I could keep the engine running by putting the choke fully on when it began to stall. As soon as I moved the throttle back to high speed, it would really start stalling. I could keep it going for about 30 seconds going back and forth to the choke position and high speed position, until it just stalled. All I needed to wait was about one minute and it fired right up. I let the thing idle and it seemed to run forever. It runs fairly long at half-throttle, but at full-throttle is when it goes within 15-20 minutes.

    Could I be losing compression as it gets hot due to sticking piston rings? When I took the head off a few weeks ago, the dome was covered with heavy baked on carbon deposits. Could the piston ring seats be so full of carbon that with expansion they are hanging up and causing a loss of compression. Seems far fetched, but I was going to pour some "Seafoam" in the cylinder and then run some thru the carb and also leave a few ounces in the crankcase oil. Hopefully that breaks down any crud in there. I'm not sure what else to look for.

    But at least I got the rest of the lawn done tonight!:cool2:

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