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I've got an old (1988) 8HP Briggs & Stratton engine (195422-0751-01) on a leaf blower with some problems.

Symptoms:

After ~10 minutes of running okay, (choke open, 1/3 to 1/2 throttle), it starts to die, almost always due to being angled in any direction on a hill. The only way to keep it from dying is to close the choke. After this period, I can try adjusting the carb mixture only to get it running another 3 minutes with 1/2 choke and 1/3 throttle. Letting it sit ~1 hr is the only guarantee it'll work for another 10 min.

What I've tried or replaced:

  • Carb replaced with new from ebay. Adjusted mixture screws (per engine user manual's instructions -- 1.5 turns on main, 1 turn on idle) and readjusted for hours in order to get a mixture that lets it run for a few minutes.
  • Removed fuel tank, outlet nozzle, and hose to clean and inspect. They're fine.
  • Used new gas.
  • Replaced gas cap.
  • Inspected air filter and oiled pre-filter (per manual's instructions). They're fine.
  • Tested compression. Results consistently ~137 psi.
  • Changed oil.
  • Seafoamed gas.

Additional notes:

  • When it's dying and I close the choke (to revive it), exhaust spits black smoke.
  • When main jet is opened more than 2 turns (which the engine seems to need at the time to run), there's sometimes a few drops of fuel coming from the bottom of the carb.

What am I missing?

  • 1
    Sounds like it has a vacuum leak which opens up after it gets warm, like the metal is warped but only when hot. Dunno, just a thought. – Pᴀᴜʟsᴛᴇʀ2 Oct 25 '14 at 1:46
2

If my memory serves me properly that's an old 'flat head' briggs motor.

  1. Set your float. There is a tab on the floats. When you remove the carburetor float bowl set the floats to set parallel to the edge of the float bowl mating surface of the carb. This is common with new carbs oddly enough, I think briggs calls it a tang. It's metal and the floats should be plastic. Bend the metal to adjust.
  2. This is old, so your gaskets are probably shot. If you don't have new ones, use some RTV on either side between the carb and the engine. If you have any air leaks it will run lean and you will be turning out your mainjet, when it gets hot, it won't run, you will choke it to get it richer and start blowing black smoke. When it dies the built up fuel from the choke will run out of the cracks in the gasket and make you think you have a fuel leak.
  3. Check the primer bulb. IF it has cracks, replace it. You could have a leak from that but I doubt it.

I truly believe this a float issue and an air leak on the gasket between the motor and the carb.

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