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#12247751 - 05/16/17 08:35 AM Merc Carb Flooding
DanH Offline
Pro Angler

Registered: 04/28/05
Posts: 531
Loc: Justin, TX
I'm about at my wits end... I've been reading posts on this for days, still haven't found my culprit.

1988 Merc 35hp, oil injected (no longer in use, I premix)

The boat was running ok for the first few trips out this spring but I had two problems pop up. Starter wasn't turning the boat over and I found the carb was puking gas. The gas actually got into the starter and turned it into a mess, 2 of the wires to two of the brushes were broken off. So now I have a new starter on the boat. I've cleaned the cab bowl out, attempted to get the float height adjusted properly, but the carb will still bubble fuel out of the main nozzle when you prime or start it. If I turn it over a few times it's a fairly steady stream of gas dripping off the bottom of the carb.

Diagram for those of you not familiar with this pressure style carb:

When I took the carb out the first time I did all the fuel lines because I discovered the liner of my atwood fuel hose had come completely apart. So all filters and lines have been replaced. I have a water separator canister style filter out on the back by the tank, before the primer bulb. I've had it setup this way for a few years, no issues. However I did noticed that there was an inline filter between the fuel pump and the carb, this didn't make much sense to me, I figured you'd want it before the fuel pump so I bought a new one and put it there. So we have Tank->Water Sep->Primer->outboard connector->Inline Filter->Fuel Pump->Carb. Could have moving that inline to pre pump instead of post made a difference?

When adjusting the float tangs there was a larger gap that spec's (1/4"), it was about 1/16" more. So I bent the tab putting it back to 1/4". However in my mind this allows the float to come up higher, maybe making the problem worse. Pic attached to show this.

Float is ok, no leaks.

Pump could potentially have too much pressure? So I got a kit to do that next.

Seems to me this keeps going back to a float issue, but the tangs are spec I believe. The needle valve was replaced, and it moves freely in the housing for the most part, I have noticed sometimes it doesn't freely fall when dry after working on it for a little while. When blowing in the fuel hose it does block air when you flip it over, and open when you turn it back upright.

The paper notch is 1/4", I've bent the tang end to meet this.

One other item I read about was something in the jet, so its'bubbling fuel out instead of spraying it. I'm not quite sure yet what to try to disassemble to check that. I don't know what screws I can just take out and which ones I need to count rotations.

What else am I missing here?

Here is a rather poor video of the carb when I turn it over. You can see all the fuel sloshing around in there when the starter is disengaged. if I can get a buddy over to hold the camera instead of strapping it to the outboard I'll try to get a better video.

Edited by DanH (05/16/17 08:41 AM)

#12248666 - 05/16/17 06:04 PM Re: Merc Carb Flooding [Re: DanH]
opus Online   content
TFF Celebrity

Registered: 07/15/07
Posts: 7050
Loc: West Tx no. of waco
Sounds like needle & seat bad

#12249395 - 05/17/17 08:12 AM Re: Merc Carb Flooding [Re: DanH]
boatman025 Offline
Pro Angler

Registered: 07/16/10
Posts: 548
Loc: Wylie
Float may have gas in it buy new float
Hughes Marine Service
Wylie ,Texas


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