Briggs 18.5 42A707 runs rough after getting hot

Discussion in 'Mechanic and Repair' started by tminnie, Jul 4, 2006.

  1. tminnie

    tminnie LawnSite Member
    Messages: 3

    I have a Briggs 42a707 that is driving me crazy!:hammerhead:
    It is mounted on a lawn tractor.
    Now the meat of the problem:
    After running at full RPM (while cutting), after about 30-mins. it acts like it is starving for fuel. Sometimes by pulling the chock out, I can get it running somewhat. But after letting it cool down, I can restart it, runs great at low/high RPM. I've let this thing run at idol for almost an hour, and it will run fine. I've totally cleaned the engine, checked/replaced all filters, flushed fuel system, new gas. checked carb inside and out (floats, needle/seat). It seems like it is vapor locking. My next move is to get a fuel pump repair kit, but I'm on an limited budget. HELP!!! I have lawns to cut, and at this rate, I'd be better off with a push mower.:laugh:
  2. newz7151

    newz7151 LawnSite Silver Member
    from Tejas
    Messages: 2,419

    Taking into account what you have already done, is your fuel cap venting properly?
  3. Restrorob

    Restrorob LawnSite Fanatic
    Messages: 11,029

    Same thing I was thinking newz.....
  4. tminnie

    tminnie LawnSite Member
    Messages: 3

    Yep, checked that too.. even took it apart to see if there was something "living" in it. Could blow air through it. This problem just started a few weeks ago. If's been running fine up until than. At first I thought it was a bad tank of gas, but I emptied it out, and did a flush. Now I checked the fuel tank and it's 1/4 full.
  5. tminnie

    tminnie LawnSite Member
    Messages: 3

    First off, I'd like to say Thank You! for a fast reply to my post. I have done the following, and as of now, I think you guys where on to something. I took apart the gas cap and removed the check-valve seal. I didn't find anything living in it, checked the foam button to make sure it was clean. Filled the take to full and ran it full tilt for over 30-mins. and it ran perfect. Guess it was the gas cap.....I have a large job to do tomorrow, and we'll see what happens. Thanks again!!! You guys are great. ----- Tom
  6. Jim@MilkyWay

    Jim@MilkyWay LawnSite Senior Member
    Messages: 472

    If it does it again, snatch the cap off the tank, put it back on and see if it runs OK at WOT for another 30 min. You _are_ most likely 'running out of gas' for one reason or another; and I do not mean because of an empty tank.
  7. Jim@MilkyWay

    Jim@MilkyWay LawnSite Senior Member
    Messages: 472

    Forgot to mention; is it possible you have a fuel line collapsing after the engine compartment heats up?
    I don't know, it sounds good to me.

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