1. Missed the live Ask the Expert event?
    Not to worry. Check out the archived thread of the Q&A with Ken Hutcheson, President of U.S. Lawns, and the LawnSite community on the Franchising Forum.

    Dismiss Notice

Briggs Engine Sucks Too Much Gas

Discussion in 'Mechanic and Repair' started by taelwind, Oct 24, 2012.

  1. taelwind

    taelwind LawnSite Member
    from Leander
    Posts: 6

    310777 0112-E1 16.5 HP OHV Single Cylinder side draft carb, gravity fed.

    Rebuilt the carb. Mower only starts when I remove the air filter from the mower. It's a little reluctant to start, but it will run. The running condition described as reluctant and not as fast as one would think the engine should. A tug on the governor and it runs faster. I let the engine run full speed under no load. - I filled the gast tank with about an inch of gas in the bottom - man-oh-man does it suck down the gas. As the level in the carb bowl gets low - right before it runs out of gas - the engine speeds up and runs like it should, then of course, due to no gas, it dies.

    I have the deck removed, the mower will drive around, no problems. The engine will turn over by hand with almost no resistance, it feels like compression is being shoved back out the intake. I pulled the OHV cover and all moves like it should. Anybody have any experience with this issue. ?

    :wall:drinkup:
     
  2. dutch1

    dutch1 LawnSite Silver Member
    from Jayhawk
    Posts: 2,231

    Nikki or Walbro carb? If it's a Nikki, the main jet(117A) is held in the fuel transfer tube(135) by a very small oring that is part of the main jet. If it is loose and floating around or you lost it in the rebuild process, the engine will overfuel. Just a quick thought off the top of my head.

    Don't know if this will get you to the diagrams or not but here's a link:

    http://www.wiseequipment.net/pages/...rburetor,_Overhaul_Kits/3107770112E1/55130005

    Did you check the valve clearances? Adjust your valves to spec then do a compression and leakdown test. If you're getting blowback through the carb you may have an intake valve out of spec.
     
    Last edited: Oct 24, 2012
  3. piston slapper

    piston slapper LawnSite Platinum Member
    Posts: 4,240

    Ditto Dutch....
    If that jet gets loose in the carb it will run like junk until it is almost completely out of gas....
    I hate when people clean their carb and they lose the jet when they blow it out with compressed air...
    Posted via Mobile Device
     
  4. dutch1

    dutch1 LawnSite Silver Member
    from Jayhawk
    Posts: 2,231

    Yea, Slapper, I had a guy who had been into his Nikki carb---when he put it back together he put the main jet into the inlet needle port thinking it was the seat.:hammerhead: Terrible design for a carb.
     
  5. taelwind

    taelwind LawnSite Member
    from Leander
    Posts: 6

    Sorry, it's a walbro. I throw those nikki carbs out. Nikkis cause me nothing but trouble. Good to know that about the nikki though.
     
  6. taelwind

    taelwind LawnSite Member
    from Leander
    Posts: 6

    The previous owner cross threaded the spark plug. I was able to run a thread restorer into the opening and get a new spark plug installed, not able to get my compression tester in there, or i would. Thus the reason for for my posting here.
     
  7. herler

    herler LawnSite Fanatic
    Posts: 5,145

    Usually when small engines suck down the fuel it's because there is an air leak between the carburetor and the throat of the engine along the lines of the intake manifold, also it is possible the pcv tube is sucking air, the only other possible explanation is a fuel line leak or the carb float... I am leaning towards the intake manifold air leak due to the carb rebuild or something that didn't get hooked back up right.

    However...
    The air leak scenario usually also results in more than the usual amount of power.

    And it still won't suck gas at more than 1-2 gallons an hour...
    You might have a fuel leak between the fuel tank and the carburetor as well.
     
  8. joe billy

    joe billy LawnSite Member
    Posts: 35

    That's absolute horsehockey. The stupidest post. I've ever read.
    If you had an intake leak it would run lean and use less fuel.
    It would also make less power as a result of starving for gas.
    I surely hope you don't work on other peoples mowers.
    Posted via Mobile Device
     
  9. herler

    herler LawnSite Fanatic
    Posts: 5,145

    Well billy, you're not contributing the solution so let me speak from what happens to the 150cc GY6 engine when it sucks air and you believe what you want but when an engine runs lean it runs harder and stronger and creates even more suction which results in the carburetor feeding a TON of fuel, and maybe your engines lean out but a small enough air leak doesn't and that results in a never-ending cycle so whether you believe me or not an air leak on the intake end can (and will) result in higher fuel consumption.

    How did I come up with this analysis?
    The guy just rebuilt the carburetor, which means he removed, and re-installed it.
    Thus it is possible that a small air leak could have worked itself in, maybe a gasket didn't seat correctly, perhaps somehow the carburetor did not get re-installed the way it should have been, and it is a likely cause of the malfunction, I never said it was the cause of the problem, I said it was a possibility.
    Air leaks DO include vacuum lines!

    The other possibilities are being, will be, or have been covered.
    I am not interested in discussing those, I am discussing the fact that the carburetor rebuild was likely the source of the problem.
    Air leaks DO include vacuum lines!

    On that note, a new carburetor and gasket set might likely fix things as well.
     
    Last edited: Oct 25, 2012
  10. taelwind

    taelwind LawnSite Member
    from Leander
    Posts: 6

    The carb was rebuilt. I have done many of them for briggs walbro. There are no vacuum lines. All new gaskets at all locations. There are no fuel leaks or they would certainly show up. The fuel line is new, the fuel filter is new.

    I'll be pulling the head off shortly and taking a look. before then, I may remove the intake manifold and take a peak inside to see if I can see anything wrong with the intake valve.

    I'll check the float, I did not replace it, nor did I check if for leaks. That could explain a lot. Still have to resolve the compression issue. Does not make sense to be able to turn engine by hand and not have resistance, but yet still be able to run and drive. I may go ahead and reinstall the deck and see if it bogs down.

    thanks to all who have given me there two cents.
     

Share This Page