18 horse briggs carb rebuild issue

Discussion in 'Mechanic and Repair' started by cableman, Apr 22, 2006.

  1. cableman

    cableman LawnSite Member
    Posts: 14

    Everyone I just rebuilt my carb on a 18 horse briggs model 422437 and since my rebuild I have to run almost full choke when I engage the deck. I have to do this for about 2-3 minutes before I can remove full choke. The engine will start up just fine and I can drive the Grasshopper around but as soon as I turn on the deck it will kill the engine if I don't have the choke on. Now once the engine is warmed up, I can engage the deck at anytime without the choke on. Does anybody have an idea what may be wrong? The carb is the one that has no adjustment except for idle mixture.

    Thanks
     
  2. Restrorob

    Restrorob LawnSite Fanatic
    Posts: 11,023

    Sounds like you may have the low speed adjusted a little lean for making the transition to the high speed circuit. Try backing the low speed adjuster out until the engine starts to labor or run rich, Then adjust back in slowly until it just does smooth out a little. If that doesn't do it maybe there is still a restriction in the low speed circuit. What method did you use to clean the carb. out ? Are you sure the two brass springs in the fuel pump didn't move out of place while installing the pump block ?
     
  3. totallawncare912

    totallawncare912 LawnSite Member
    Posts: 80

    there should be another screw in front of the carb right below the fuel pump and that is your adjustment screw and you probably have to run it a little bit rich to get it not to do that i had a similiar issue with a 16hp briggs Twin 2 also did you rebuild the whole carb needle valve and all float etc. ? all gaskets did you get all the old gasket residue off the pieces ?
     
  4. cableman

    cableman LawnSite Member
    Posts: 14

    When I rebuilt the carb I did replace the float needle and the low speed adjustment needle. My kit didn't come with seat for either needles. When I cleaned the carb I used carb cleaner and compressed air(it's all I had). Do you know by chance how many turns out should be a starting point on the low speed needle?
    Cory
     
  5. Restrorob

    Restrorob LawnSite Fanatic
    Posts: 11,023

    1 turn for a starting point then adjust as I mentioned above.
     
  6. cableman

    cableman LawnSite Member
    Posts: 14

    I set the needle so I did have a good idle but when I went to high speed it acted as if it was getting to much fuel. I adjusted the screw to have good high speed and now I have a little rough idle. Is this normal operation or do I have something else I need to look at?
    Thanks
     
  7. Restrorob

    Restrorob LawnSite Fanatic
    Posts: 11,023

    These old L head engines are known to not idle really smooth due to the cylinder configuration, Just adjust until you have the best idle to high speed response and check the plugs after a couple days of running to see how they are burning.
     
  8. cableman

    cableman LawnSite Member
    Posts: 14

    Will do thanks, for your all your help.
    Cory
     
  9. lucforce

    lucforce LawnSite Member
    Posts: 223

    The opposed flat-head Briggs twins have the valve timing set differently for each cylinder. I always assumed that it was to help get the things spinning easier to save the starter. At least that was the only reasonable answer. The condition really causes idle issues for engines that are not in otherwise top shape.
     

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