Briggs carb runs rich!

Discussion in 'Mechanic and Repair' started by Poot, Aug 3, 2007.

  1. Poot

    Poot LawnSite Member
    Messages: 24

    Hello y'all. I have a 17hp Briggs I/C on a Murry LT that will NOT run right. I've soaked the carb for two days in a brand new bucket of carb cleaner, put in a new kit including the needle valve seat, and today replaced the high speed jet with a new one. No matter what I do, it runs rich and yes the choke is full off. It will ALMOST runs smooth but is just short of and spews out small clouds of black smoke. Another thing is the air mixture screw will not kill it if screwed in completely. This has driven me nuts!!!! What in the H___ am I missing??? Someone suggested pulling the choke on to maybe 45 degrees. My reply was it's already running rich so why would I add choke to an already overly rich condition!!! Oh, and I've replaced the plugs too and the spark is great. ANYONE with ANY idea as to why will be GREATLY APPRECIATED!!!!!!!!!
  2. Bill Kapaun

    Bill Kapaun LawnSite Senior Member
    Messages: 964

    "put in a new kit including the needle valve seat"
    Do you mean for the float? If so,how about the needle?
    Was there an "o" ring in the seat that may or may not have been removed?

    Is the float punctured/saturated with fuel so that it doesn't have the proper buoyancy?

    What are the engine #'s?
    That way we can tell exactly which engine/carb it is, instead of guessing.
  3. Restrorob

    Restrorob LawnSite Fanatic
    Messages: 11,029

    There could be other issues, Can't tell without model and type numbers as Bill mentioned.

    Is this a Walbro or Nikki carb ?
  4. Poot

    Poot LawnSite Member
    Messages: 24

    LOL! Thanks for the replies and sorry about that fella's. Guess some numbers would've been a little helpful huh. The model is #42A707, type #2653E1.
    The seat; Yes I meant the float's needle valve seat and replaced the needle valve too. There was no "O" ring in the seat either before or after. The float; it's good, no fluid inside, and is adjusted using as most everyone recommends a #4 bit at the opposite side from the hinge pin. The air filter is new/clean. As for the make of carb, assume it's a Nikki. I say this because on a Walboro I always see their name somewhere on one but this has no name anywhere but as I said, that's an assumption on my part and I could very well be wrong. I bought this mower and the seller said it hadn't been sitting up long. I knew it had because smelling the gas told me it had sat a LONG time. It ran but only if the choke just off of full on. After the rebuild it runs and runs close to right (u can tell it's almost there) with the choke full off but sputters a lot and when it does it lightly black smokes. Every once in a while it'll smooth out for a few seconds then start lightly sputtering again. It's so close to running right it ain't funny....but doesn't. :cry: I forgot to mention this. After letting it sit for a while I can look through the carb and into the intake (straight below the carb) and there's a small puddle of gas standing. First thought was after turning it off MAYBE gas was seeping past the new needle valve seat. Then I remembered it was doing this before I rebuilt the carb, did it after the rebuild, and after taking it off/apart AGAIN and installing a new seat for the float's needle valve, it's still doing this. ARG!!!!!!!!!!!! :hammerhead:
  5. Bill Kapaun

    Bill Kapaun LawnSite Senior Member
    Messages: 964

    Did you replace the fuel pump kit at the same time? Could be a pinhole in the diaphragm allowing excess gas to be sucked in?
    Is this a 3 or 4 screw fuel pump?

    It might be as simple as water in the gas? Did you drain the tank completely? If you think it might be water, put a few oz. of Gas Dri in the tank.
    Alcohol absorbs water. Bad thing about it, it absorbs water from the atmosphere/condensation when just sitting.
  6. tank

    tank LawnSite Member
    Messages: 33

    Air cleaner you said new clean which is it new or cleaned?
  7. Restrorob

    Restrorob LawnSite Fanatic
    Messages: 11,029

    Never used a drill bit to set a float before, With the upper body inverted the float should be parallel to the gasket surface, I adjust about 1/16" higher on the side away from the pin.

    Check the pilot jet (the screw on the lower front of the base). There is supposed to be a small hole in the tip of this pilot jet, Use a bristle out of a hand wire brush to make sure it's open.

    Also, I see you're in Tennessee. Maybe a higher altitude ?
    You could try the high altitude jet part# 693499 with the smaller port and see if that solves the problem.
  8. John Stiles

    John Stiles LawnSite Member
    Messages: 42

    What kind of exhaust[muffler]is on it? Sometimes the wrong back pressure will cause rich/lean conditions....?
  9. Poot

    Poot LawnSite Member
    Messages: 24

    When I said the filter was new/clean, I meant it is BRAND new and clean. Not one that's recently new and has been used a little. Some owners who say new can say "It was new....two months ago" but don't consider they could've used it in very dusty conditions so while "new" in their eyes, it could be dirty/clogged. So, it's new AND clean having never been used other then running it in my garage. Ooooook, the float is about 1/16 off level to the high side, inverted. When u said to check the pilot jet on the front lower base. Do you mean the air/fuel mixture screw? I've ran a thin wire through ALL the openings as far as a wire would go and yes I've done so in that opening as well. Just wanted to see if you and I were talking the same lingo here. As for the muffler, I can't SAY that it's stopped up but putting my hand in front of it it does have a LOT of exhaust pressure. I did this to another mower to compare and the pressure feels fairly equal to me. As for altitude, I live in Southwest Tennessee and it's flat here but a high altitude jet IS a thought. I just bought/installed a new jet but it didn't help so maybe your idea would work. It still doesn't ID the cause/reason for this problem which I'd like to know for future use and is a bandaid but heck, if it worked I'm all for it. This mower was bought from a local Walmart (he said) and did not come from a higher altitude area but that doesn't mean it hadn't been changed by someone at some point. However, the jet I just installed was "standard" and not the high altitude jet which was an option. And I'm not trying to poo-poo anyone's helpful idea's or thoughts, it's just that so far I've tried what's been suggested with no change in the problem which is why I've become so frustrated. But y'all please keep trying and I'll keep doing and maybe between all of us we'll hit upon the cause and a fix!!!!!
    And yeah, ANY/ALL ideas are GREATLY APPRECIATED!!!!!

  10. Bill Kapaun

    Bill Kapaun LawnSite Senior Member
    Messages: 964

    Well, the elevation at your airport is 243', so I doubt you would be considered "high altitude"! (5000') Unless you live on a mighty steep mountain:)

    DID you do anything to the fuel pump?

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