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Briggs lawnmower cutting out

Discussion in 'Mechanic and Repair' started by adameid, Oct 30, 2006.

  1. adameid

    adameid LawnSite Member
    from sydney
    Posts: 16

    Hi all,
    I have a briggs lawnmower which Ive had for 2 years. Recently its cutting out at all speeds. I ve replaced the spark plug and air filter but still the same..
    I also noticed when I removed the air filter/hosing and started the engine a lever on carbby moves back and forward causing the engine rev high then low.
  2. khouse

    khouse LawnSite Bronze Member
    Posts: 1,465

    remove carb and dissasemble,spray out with Brakleen,blow out with compressed air,reassemble,drain fuel cell,spray out with brakleen,blow out with compressed air,add fresh fuel and pull the rope.
  3. adameid

    adameid LawnSite Member
    from sydney
    Posts: 16

    i removed the carbby and cleaned it out but still having the same problem.
    The mower is running like an airfilter blocked.
    I replaced the spark plug recently so its new. I pulled out the plug again and noticed it was black so the mower is running rich. I suspect there must air restriction but dont know where can anyone help pls

    Thank you
  4. Restrorob

    Restrorob LawnSite Fanatic
    Posts: 11,023

  5. adameid

    adameid LawnSite Member
    from sydney
    Posts: 16

    hi restrorob,
    Sorry about that The mower is Briggs and Stratton 35 Classic
    Model type Code
    98902 2210 B2 03061751

    I hope that helps.
    I started it again today its backfiring,cutting out and running rich.
    As described earlier Ive cleaned the carbby replaced the plug cleaned the air filter still no go. Can you pls help
  6. Restrorob

    Restrorob LawnSite Fanatic
    Posts: 11,023

    There is really nothing to this plastic carb., Hunting (running high and low) is a sign of running lean. Possibly trash in the main jet or air leak somewhere.
    Since you have already cleaned the carb. with no better results but now say it's running rich I would suggest checking the flywheel key. A partly sheared key will throw ignition timing out and could cause one to run as you describe now.

    You stated you replaced the air filter then later said you cleaned it ?

    Food for thought; I have seen used air filters that looked good but did indeed have a air flow restriction.
  7. adameid

    adameid LawnSite Member
    from sydney
    Posts: 16

    hi restrorob,
    Can you pls tell what is the purpose of a carbby Diaphragm and how can one tell if it needs replacing. The diaphragm on the mower isnt damaged at all but could it cause the mower to starve for air even with the air filter off. Im no expect but it appears its starving for air. Even the sparkplug is coloured black soot.

    what is the gap between the coil and flywheel??

    Thanks again
  8. Restrorob

    Restrorob LawnSite Fanatic
    Posts: 11,023

    Your engine is not actually starving for air but getting too much fuel for the amount of air the engine requires to operate properly.
    The diaphragm is nothing more than a fuel pump. It's action is to pull the fuel up the long tube sticking down in the tank and transfer it to the small cup in the top of the fuel tank. This is where the main jet is submerged below the fuel level in this cup, Then the engine vacuum pulls the fuel up from this cup into the carb. being atomized then enters the combustion chamber via the intake valve.

    The fact that it is running rich shows the diaphragm is pumping the fuel.

    The coil to flywheel gap is .006" -.010" or any standard business card thickness.

    It may be possible the primer bulb check valve could be causing the problem, But it's a hard call without seeing the unit and what it's doing.

    I no longer do much work on the small mowers due to labor rates and the price of a new units from the big box stores. But when I do and the unit has carb. issues it's cheaper in the long run to replace it than waste time repairing. For instance a new carb. including diaphragm for your unit is only $ 22.80 US dollars.

    Below is the check valve I'm speaking of, It's behind the primer bulb.....

    Briggs 98902 Carb.jpg
  9. shopteacher

    shopteacher LawnSite Member
    Posts: 60

    Clean the carb again, and again if needed. Those carbs can be finicky if you don't do it right.

    I'll bet you still have dirt lodged somewhere.

    I'm not an expert, but have solved alot of these types of problems with a very thorough cleaning, sometimes more than once or twice.
  10. adameid

    adameid LawnSite Member
    from sydney
    Posts: 16

    hi restrorob,

    Thanks for your advice again. I dismantled the carrby and cleaned it now the mower is working like new one.
    Thank you I should buy u a beer.
    Iam going to ask you question in a new thread.

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