Too much fuel too fast

[robotmark]

I have a 1974 Johnson 40 hp 40E71G. It starts up and runs right away, and then immediately floods. If I disconnect the fuel line the engine will run perfectly until it’s out of fuel. If I reattach the fuel line it immediately floods again. The carburetor and fuel pump seem to be operating normally so I’m thinking it’s an issue with the fuel line. Has anyone experienced this previously and have any tips on where I should start my troubleshooting?

Thanks!

[aquasonic]

Is the float assembly working properly? Wonder if it’s getting stuck down intermittently.

• This reply was modified 4 years, 2 months ago by aquasonic.

[robotmark]

It appears to be because the engine will run through all its onboard fuel. This carb has been rebuilt within the last year so I’d not like to do it again, but I’m worried it may ultimately be the culprit.

[Mumbles]

I think it’s an issue with the float valve in the carburetor. It could be worn or dirty allowing the fuel to flow right thru it when hooked up to the hose. The problem could also be caused by the float being heavy and soaked with fuel, stuck, or not set properly. These motors used a cork float and using gas containing ethanol will destroy the coating on the float which will then soak up fuel. Ethanol gas will also damage the fuel lines causing small pieces to break off which can get caught in the float valve and cause flooding. It might be time to take the carb off and install a new carb kit after cleaning it really good.

[aquasonic]

When you disconnect the fuel line the source of the flooding fuel is cutoff. No more pressurized fuel supply. The flooding stops.

[fleetwin]

How do you know the carb is OK? Just because you have cleaned/rebuilt it, doesn’t mean it isn’t flooding over…But, I would think you would be able to see fuel dribbling out of the carb throat if it was flooding. Trying trimming the engine up just slightly from its vertical running position, then connect the fuel and pump the fuel bulb. You will see fuel dribbling out of the carb throat if the carb is flooding over.
The fuel pump could be damaged causing it to flood one cylinder. Remove the fuel pump, then pull the thick gasket off the powerhead. Now reattach the fuel pump to the crankcase without the gasket in place, snug the attaching screws, don’t over tighten them. Now pump the fuel bulb, you should not see any fuel spilling out of the back of the fuel pump. If fuel is spilling out, the fuel pump diaphragm is damaged. Don’t forget to reinstall the gasket afterwards, and don’t pull that fuel pump apart unless you have confirmed it is to blame. Not all fuel pumps are rebuildable, and you surely don’t want to pull it apart if it is OK…

[crosbyman]

have you done a blow test on the carb…. yes no ??

air can go in holding the carb upright air MUST not go in when the carb held upside down

if air does go in when the carb held upside down then the float/needle point is not properly adusted or the needle is not doing its job of closing fuel entry when pushed up by the floating ” float” when the carb fills up…resulting in flooding .

toilet bowl floats and carb floats work the same way 🙂

Joining AOMCI has priviledges 🙂

• This reply was modified 4 years, 2 months ago by crosbyman.

[robotmark]

I think you all have convinced me. I was hesitant to take take off the carb again because on this model it also means removing the starter motor and some other stuff in the way, so it’s fairly involved, but seems like it’s what I need to do. Thanks everyone!

[fleetwin]

Once again, is fuel dribbling out of the front of the carb? Pump the gas and have a look… Yes, removing the electric starter is a pain, but only takes a few minutes. But, please confirm that the carb is actually flooding over prior to ripping into it again…

[DAN UMBARGER]

Heed what Fleetwin says before you go thru all the labor of pulling the carb. Check the fuel pump first…the way I check them is to pull the fuel pump and reinstall the bolts thru the pump with a couple of nuts on the back side then pump the fuel bulb..if the diaphragm is bad you’ll get fuel leaking out of the pulse hole. By what you have said initially this is probably your problem but as Mumbles and the others have said it’s more than likely the float, needle and seat or fuel pump diaphragm.

[Author]

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