1978 Mercury 900 Carb problem Please Help

[mrlexmark]

I have a 1978 Mercury 900 6 Cyl 90 hp outboard. The top carb sprays fuel out the overflow spot so I removed the carb and rebuilt it. I reinstalled it and it still does it. Even when you squeeze the primer ball it sprays the fuel out the overflow spot. Any ideas on what the problem is?

 

[IamCanadian]

Re: 1978 Mercury 900 Carb problem Please Help

either the float is set wrong, or not floating at all, their may be some dirt in the needle/seat area. Should be a simple fix but it forsure has to do with the float/needle/seat.

 

[mrlexmark]

Re: 1978 Mercury 900 Carb problem Please Help

either the float is set wrong, or not floating at all, their may be some dirt in the needle/seat area. Should be a simple fix but it forsure has to do with the float/needle/seat.

I replaced the needle/seat when I rebuilt it. I sprayed it alld own with carb cleaner. The only thing I did not mess with was the float and the little spring on the float.

This would all cause fuel to spray out of the over flow valve even when you are primeing it?

 

[Maxz695]

Re: 1978 Mercury 900 Carb problem Please Help

If the float level is above the proper setting it will allow fuel to exit the overflow spewing fuel. I find it best to remove the line fiiting and the needle seat to bhe sure there is not a piece of fuel line or other gunk in there. I would also ask if you changed the little copper washer where the seat for the needle rests. If it is nicked oblonged crushed etc, it will not properly seal.

 

[mrlexmark]

Re: 1978 Mercury 900 Carb problem Please Help

If the float level is above the proper setting it will allow fuel to exit the overflow spewing fuel. I find it best to remove the line fiiting and the needle seat to bhe sure there is not a piece of fuel line or other gunk in there. I would also ask if you changed the little copper washer where the seat for the needle rests. If it is nicked oblonged crushed etc, it will not properly seal.

I went to the marina and ordered a carb rebuild kit and replaced everything. Took every screw out and sprayed it clean with carb cleaner to get all the junk out.

When i first had the problem it would only do it when you throttled it high. Then I took it out and cleaned it and rebuilt it and now right when you start it up it starts spraying out of there. even when you prime it with the ball it squirts it right out. It is the top carb and the middle and bottom one dont do it.

 

[Maxz695]

Re: 1978 Mercury 900 Carb problem Please Help

take the top carb back off the float is not closing the needle and fuel is forced out of the overflow. I would hook a line form the fuel pump to the crab after repair and assure it when held level does not leak fuel before reinstalling it

 

[Chris1956]

Re: 1978 Mercury 900 Carb problem Please Help

You are setting the carb float height to spec? BTW - the brass jet in the carb cover is the Backdraft vent Jet, not an overflow. Carbs are not meant to overflow, hence no need for an overflow