Carburetor flooding on '57 Johnson 18 hp

mud dr · Jan 10, 2011

I just finished re-building my carb on a '57 Johnson 18 hp, but it floods out when I squeeze the primer bulb.(2-3 squeezes) This engine has been retro-fitted with a fuel pump. I have tried all of the obvious fixes, leveling the float, checking for trash in the needle valve,

JKTrevecca · Jan 10, 2011

Re: Carburetor flooding on '57 Johnson 18 hp

If you hold the carb upside down (while it is off of your motor of course...) and blow into the fuel line nipple, you shouldn't be able to blow any air. Have you tried that? If you try this test and you are able to blow air, then your needle isn't seating correctly which is causing the fuel to pour straight into the engine regardless of how high your float is rising.

Joe Reeves · Jan 10, 2011

Re: Carburetor flooding on '57 Johnson 18 hp

Did you rerplace the float needle valve? If not, do so.

(Carburetor Float Setting)
(J. Reeves)

With the carburetor body held upside down, the float being viewed from the side, adjust the float so that the free end of the float (the end opposite the hinge pin) is ever so slightly higher (just ever so slightly off level) than the other end. And when viewed from the end, make sure it is not cocked.

samo_ott · Jan 10, 2011

Re: Carburetor flooding on '57 Johnson 18 hp

I agree. It sounds like the needle was not replaced and is still leaking. It's pretty much the only way that can happen.

F_R · Jan 11, 2011

Re: Carburetor flooding on '57 Johnson 18 hp

It will flood big time if the bowl vent is plugged up. But they pretty much wont plug up unless somebody deliberatly does it. Or dirt daubers!

Joe Reeves · Jan 11, 2011

Re: Carburetor flooding on '57 Johnson 18 hp

Yep, clogged bowl vent.... that slipped my mind. There was a fellow on one of these sites that had a old V4 75hp with a downdraft carburetor that would flood no matter what he did. He shipped it to me and what did I find? Clogged bowl vent.

For those that may not comprehend the term Bowl Vent, it is simply a open passageway in the upper carburetor body that leads to the atmosphere. Air that exists in the carburetor float chamber requires this exit so that the incoming fuel can enter the float chamber. If the vent is clogged, the fuel immediately flows out (floods) any other exit available.

1946Zephyr · Jan 11, 2011

Re: Carburetor flooding on '57 Johnson 18 hp

Yep, I had a clogged bowl vent stump me for a while on a 6hp Johnson once. It ran like it was flooding out bad, when I tried to rev it up. After letting it sit on the rack for a few months, I started messin around with it and saw the clog. I unclogged it, and it ran like a dream. Sold it a couple days later for $300.

mud dr · Jan 11, 2011

Re: Carburetor flooding on '57 Johnson 18 hp

A plugged up vent hole! That is something I haven't checked. I will do so first thing in the morning. I have re-built plenty of lawn mower carbs, but I don't ever remember seeing vent holes. Is this something unique to outboards?

Steve

samo_ott · Jan 11, 2011

Re: Carburetor flooding on '57 Johnson 18 hp

Joe Reeves said:
For those that may not comprehend the term Bowl Vent, it is simply a open passageway in the upper carburetor body that leads to the atmosphere. Air that exists in the carburetor float chamber requires this exit so that the incoming fuel can enter the float chamber. If the vent is clogged, the fuel immediately flows out (floods) any other exit available.

While I don't want to argue this doesn't make sense to me. Is there more to it than this? If the vent from float chamber is sealed then fuel will not go into the chamber as it will be pressurized. Thus is should act the same as if the needle valve was closed and fuel should simply stop flowing? If it starts leaking fuel, how and where does it come out? This concept has always troubled me so maybe you could explain it for me please? thx.

Joe Reeves · Jan 12, 2011

Re: Carburetor flooding on '57 Johnson 18 hp

Steve.... Can't explain it any simpler really other than there are other exits beside the float chamber vent and of course the fuel flow follows that route. Hold your finger over the exit vent hole, then pump the fuel primer bulb and observe where the fuel exits the carburetor.

The laws of physics that govern that action is over my head but it can't be argued.

samo_ott · Jan 12, 2011

Re: Carburetor flooding on '57 Johnson 18 hp

There are other exits? That would explain it. I thought there was only one exit/vent otherwise it was a sealed chamber.

mud dr · Jan 12, 2011

Re: Carburetor flooding on '57 Johnson 18 hp

Joe Reeves said:
Did you rerplace the float needle valve? If not, do so.

(Carburetor Float Setting)
(J. Reeves)

With the carburetor body held upside down, the float being viewed from the side, adjust the float so that the free end of the float (the end opposite the hinge pin) is ever so slightly higher (just ever so slightly off level) than the other end. And when viewed from the end, make sure it is not cocked.

Well, today I pulled the carb down again ( I'm way better at it than I want to be) and decided to replace the float, needle valve and seat again and adjust the float. Looks like that did the trick, so far. I will continue to test over the next few days. The real test will come when I finish my boat build and I can test it on the boat. Thanks for all the help.

Steve

kbait · Jan 13, 2011

Re: Carburetor flooding on '57 Johnson 18 hp

Missing nozzle seal between bowl and carb body will flood it too.. for future searchers. Easy one to forget

boobie · Jan 13, 2011

Re: Carburetor flooding on '57 Johnson 18 hp

Missing nozzle seal will also cause it to run lean at high speed.

Carburetor flooding on '57 Johnson 18 hp

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