Weber Marine Troubleshooting

Weber marine runs rich or Floods

  • The first thing you want to do is test the needle & seat for leaks.
  • Make sure the ignition system is up to par. Plugs, wires & distributor.
  • Check float level – while you are at it test the float for leaks.
  • Make sure the float isn’t rubbing anywhere.
  • Move the float up and down by hand to see if you feel any catching.
  • Do you see any dirt particles on the bottom of the bowl – this indicates a dirty situation and a rebuild would be in order.
    • How did the dirt get there? Is there a fuel filter and has it been changed.
  • Test the fuel pump pressure and compare with the specification in the motors manual.
  • Viton tip on the needle & seat may be damaged by ethanol, or has dirt in it keeping it open too much. When adjusting floats do not put any pressure on the needle. It’s a sure way of damaging the Viton tip.
  • I would suspect main jets size, but only if they were changed for some reason, or you are above 5,000 feet in altitude.
  • Same thing goes for the metering rods. They might be a problem if someone has changed them. They won’t cause flooding, but can cause richness.
  • Look down the carburetor at idle. Do you see gas dribbling from the venturi?

After Shutting Down When Hot The Boat is Hard Starting

  • Percolation can be a problem especially if the engine is running hotter than normal. Percolation is when you shut down the engine, gas starts to boil and excess gas gets into the intake. If you suspect this try starting with the throttle wide open to give the engine more air. Aside from that you need to find ways to cools the engine. Also be sure any vent to the carburetor is open.
  • After turning off the hot engine, look down the carburetor to see if gas is dribbling out of the venturi. That would indicate a vent problem, or a leaking main discharge. The check ball may need to be seated, or cleaned.
  • To determine if the engine is getting excess gas after turning off the hot engine, start the engine with the throttle wide open. If that helps starting then you are probably flooding the engine when hot. Don’t determine that is the way to start because too much fuel will damage the engine over time. You need to find the problem.

Adjusting Idle Mixture Doesn’t Change Anything
Be sure the idle RPM is correct. If the RPM is too high, then the idle circuit is bypassed.This is indicative of either a vacuum leak, or something is not right in the idle circuit.Unless the screws are scored that would not be the problem. Changing the screws will not change anything.Check for a vacuum leak around the mounting gasket, intake and any vacuum line coming from the intake, or carburetor.Follow all passages, blow through them to see if they are open.Look closely at the small holes in the venturi. Some are idle vents and get plugged easily.Make sure gaskets are not covering a vacuum passage.
After a rebuild and on the bench turn the idle mixture screws all the way in gently. The screws will get scored if you turn them in too hard.Turn the screws out 1 1/2 to 2 turns which is a good place to start.After the engine is warmed up and at idle RPM:

  • Alternating between screws, turn them in 1/4 of a turn, and wait for the engine to catch up.
  • Once the RPM starts to drop, turn the screw back out 1/4 turn.
  • The ultimate goal here is to get the engine to run smoothly at idle so turning the screws in and out a bit to get the best idle is OK.

I have a 9600 Weber for my 95 stingray with a 4.3. Vortec mercruiser. The boat is originally from Ocala Florida. It is going to be used in Syracuse area at 1400’. At that elevation change do I need new jets? I don’t want the new engine to run lean.

Your current jets are good up to 5000 feet.

It is important to watch your plugs. They should burn tan, or brown. White is too lean, increase the jets by .002. Black, or sooty means too rich, reduce the jets by .002.

Be very careful with the jets in your carburetor. They may not be like most carburetor. The left and right sides could be different sizes.

Why Does My Carburetor Empty Overnight?

  • The main discharge may be leaking – look down the carburetor after turning it off. You should not see gas dribbling out of the venturi. If you do reseat the main discharge checkball. Here is an article explaining how to fix this.
  • The float bowl vent is plugged somehow. This will cause gas to be siphoned from the bowl.
  • The gas tank isn’t vented causing a vacuum. Remove the fuel inlet to eliminate the tank and let site overnight.
  • Percolation – After shutting down a hot engine, the gas boils out of the carburetor. Look for ways to cool the engine.

Updated on 03/21/2022

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