Zenith 28 228 Troubleshooting

Engine Doesn’t Idle
This assumes the electrical system is up to par. Most idle problems will turn out to be electrical.

Make sure the idle fuel passage is open. Take a look at the illustration to find where the passage are located.

Make sure the idle discharge holes are clear.

Make sure the passage from the air bleed to the adjusting needle is clear.

Check for vacuum leaks.

Are the throttle plates in correctly with any taper going towards the top of the carburetor?


Is gas coming over the top of the carburetor, or out of the throttle shaft?

  • Test the needle & seat
  • Test the float – can you hear gas sloshing around? If the engine has been sitting for a long period of time, then you need to test the float by heating up a pan of water just prior to boiling and immerse the float. Look for any bubbles.
  • Move the float up and down and look for any catching. The float pin may be worn.
  • Test the fuel pump pressure. Should be close to 4 lbs. New pumps are especially suspect because the quality isn’t good these days.
  • The float level would not cause a flooding unless it was way off.
Carburetor Parts

Only Runs With Choke On

This means you have too much air, or not enough gas. Here are some possibilities not in any order.

  • Fuel filter clogged.
  • Fuel link kinked.
  • Fuel pump weak.
  • Carburetor has been coated with varnish which can result from sitting too long.
  • Passages clogged. Spray carb cleaner through each passage to be sure it goes all the way through.
  • Float out of adjustment.

Why Engine Pops When Starting?

Most likely it’s a problem of not enough gas.

1st look down the carburetor (engine off), pump the throttle once. You should see a squirt of gas going into the bore. The accelerator circuit should provide and extra squirt of gas when starting cold. The engine needs this.

Other than that look for reasons the gas is low in the float bowl.

  • Sticking needle & seat
  • Float off adjustment
  • Weak fuel pump
  • Clogged fuel filter.
  • Kink in the fuel line.
Updated on 04/24/2021

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