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16 HP Briggs Vanguard surging

Discussion in 'Mechanic and Repair' started by Budman, May 24, 2004.

  1. Budman

    Budman LawnSite Member
    Messages: 65

    I have an early 90's model Briggs 16 HP Vanguard that started surging over the weekend. It was running fine all afternoon, but when I dropped it down to idle before putting it away I noticed that it was surging badly. It surges at idle or part throttle, but smooths out at higher RPM's. Applying patial choke seems to smooth it out. My first thought is that I picked up some crud in the fuel. Does anyone have some ideas to try out before I look into removing the carb and going through it? Air filter is clean, fuel filter (clear) does not appear to have anything blocking it.

    Thanls for any suggestions!
  2. Budman

    Budman LawnSite Member
    Messages: 65

    Does anyone have any ideas on this?
  3. sawman65

    sawman65 LawnSite Senior Member
    Messages: 754

    sounds like you have some crud in the fuel pull off the carb and clean it the clean the whole fuel system
  4. Budman

    Budman LawnSite Member
    Messages: 65


    I thought I had found the problem! When I pulled the air cleaner base off, I noticed one of the bolts that retains the carb to the manifold had backed off. I sprayed a little starting fluid around the carb base and it seemed to smooth out. Pulled that carb and found that most of the threads were stripped. I was able to get it just tight enough with the remaining threads - added some Locktite for insurance. While I was at it I pulled the shroud and housings and cleaned the vanes. Put everything back together, and now it is surging worse than before.

    Could this be a governor adjustment issue? I don't understand why it would start acting up all of a sudden. If it was a vacuum leak, it would make sense - could have worked loose from vibration. This has me stumped.

    Does anyone have any ideas on how to determine if it is a governor problem? Would a governor suddenly "go wrong"? Any ideas on things I can try, such as governor adjustments?

    Thanks for any help you can provide. Meanwhile, the grass keeps on growing.... :angry:
  5. mudpie

    mudpie LawnSite Member
    Messages: 45

    it`s probably not a gov unless you didnot get the carb. back on right. i would say its in the carb. pull the air filter off and start the mower then then manually choke the engine a little if it acts like it wants to smooth out the carb is dirty or out of adjustment usually if one will run at high speed but not idle all you need to do is open the low speed adj. more 1/8 turn will usually do it . did you replace the carb. intake gasket when you had it off
  6. Budman

    Budman LawnSite Member
    Messages: 65

    I had the phenolic spacer between the carb and manifold turned around the wrong way. It has a little dowell on one side that is supposed to fit into a hole in the manifold. It is very small, maybe 1/16 of an inch, so it is easy to miss. Turned it around the right way, and it fired right up and ran fine. As Homer would say, "Doh!"

    BTW - regarding carb idle mixture adjustment, how do you typically set these? I turned it in until it started to run rough, then backed it out 1/2 turn. Is this in the ballpark?

    Thanks for all the help!
  7. mudpie

    mudpie LawnSite Member
    Messages: 45

    adj idle mix needle to run smooth and accelerate smoothly

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