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20 hp briggs running rich, help

Discussion in 'Mechanic and Repair' started by jandjsales, Jun 26, 2006.

  1. jandjsales

    jandjsales LawnSite Member
    Posts: 8

    Hi guys, i'm new here.
    my mower has a 20hp briggs,approx 2002 model, it started running real rich and no power, i removed carb, cleaned all the passages and never did see anything, i've went through the same process three times, with same results, finaly i bought a gallon of carb cleaner, soaked it for a while and blew out all the passages again. the thing is still blowing black smoke and has no power. plugs have good spark, filters are clean. i work on pressure washers, and other spray equipment, but my own mower has me stumped. what am i overlooking???


    jeff grant
    jandj sales
  2. MowerMedic77

    MowerMedic77 LawnSite Bronze Member
    Posts: 1,164

    "plugs have good spark" but what do the plugs look like, meaning are they fouled? Without your exact model#'s off you motor I will guess you may need a valve adjustment.
  3. jandjsales

    jandjsales LawnSite Member
    Posts: 8

    plugs look good, i don't have model number handy, but its a 20 HP inteck v twin. i would go along with the vlave adjustment, but this was a problem that started suddenly, i've never heard of valves coming unadjusted all of a sudden, but i will check that.

    got any other ideas, let me know.

    thanks, jeff
  4. Jim@MilkyWay

    Jim@MilkyWay LawnSite Senior Member
    Posts: 472

    ... filters are clean...
    Which filters?
    Did you put in a _NEW_ air filter? I had a filter clog even though I washed the foam pre and "tapped" the paper element more than instructed/suggested in owners manual, but it still clogged, and I am home owner, not commercial.
  5. MowerMedic77

    MowerMedic77 LawnSite Bronze Member
    Posts: 1,164

    Valves don't suddenly come unadjusted, the metal surface between the valve and the rocker arm wears over time and with most OHV engines the settings are small in the lower .004"-.010" depending on your model and being off by a few thousands will make a big difference in performance. But you are saying it is running rich(blowing black smoke and loss of power) but not fouling your plugs:confused: Is your choke opening completely run the unit without the air filter installed and see if the butterfly is staying open

    FIXDISS LawnSite Senior Member
    Posts: 445

    Sounds like choke not openning up fully or improper float setting . Did you replace the float ,needle and seat ??
  7. jandjsales

    jandjsales LawnSite Member
    Posts: 8

    OK, you got me on that one, the plugs are fouled when it loses all power and shuts down, i clean them thouroughly and put them back in and they are fine for a few minutes. the plugs are pretty new. I will adjust the valves and go ahead with new plugs, if that doesn't solve it i'll be back.

    Thanks for the input.
    Jeff G
  8. jandjsales

    jandjsales LawnSite Member
    Posts: 8

    who ever said the valves were out of adjustment was right, a push rod was bent and off the rocker. the intake valve had some crud around the stem and in the guide the valve wasn't opening and closing properly, luckily it wasn't bent. it blows my mind, that it wasn't running rough. it would seem to run fine for a minute and then start puffing smoke again. it wasn't noticed to be skipping, popping or anything. i could've sworn it was a carb problem.

    Thanks for the advice,

    Jeff Grant
  9. tkelly

    tkelly LawnSite Member
    Posts: 3

    I have a 20 hp Vanguard (351447) made around 2000 with maybe 50 hours on it. I am having the same problem and I have checked the valves on one side so far and am ready to go out and check the other. I and a friend who is a small engine mechanic are totally stumped but we both feel the next step is the valves. I am going to hope this fixes it.

    Thanks for everyone's input and this forum.

  10. khouse

    khouse LawnSite Bronze Member
    Posts: 1,465

    that would have stumped me because all indications pointed to the carb. good job on all who posted!

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