1978 Mercury 900 (90 hp) outboard stalls out when you hit 25 mph

[mrlexmark]

I have a boat with a 1978 Mercury 900 90hp outboard. The motor runs great until you hit 25 mph then it starts to bog down and stall. Any ideas on what the problem could be?

I thought the gas cap wasnt venting so i bought a new cap and it still does it. so I drilled a small hole in the top of the gas tank to see if that would work and it didnt.

 

[michaud500]

Re: 1978 Mercury 900 (90 hp) outboard stalls out when you hit 25 mph

Check all hoses or replace!!! Check primer bulb!! Make sure to use mercury parts!!!!!! Probably an air leak

 

[Texasmark]

Re: 1978 Mercury 900 (90 hp) outboard stalls out when you hit 25 mph

When it does it squeeze the bulb. Does it recover? If so, fuel pump or air leak as mentioned.

Mark

 

[mrlexmark]

Re: 1978 Mercury 900 (90 hp) outboard stalls out when you hit 25 mph

So I pulled the cover off when I was running it and there was fuel squirting out the carb. I circled in red where the fuel is coming from.

 

[mrlexmark]

Re: 1978 Mercury 900 (90 hp) outboard stalls out when you hit 25 mph

also I did replace the fuel line, the primer ball and fuel filter

 

[Maxz695]

Re: 1978 Mercury 900 (90 hp) outboard stalls out when you hit 25 mph

thats the overflow showing your float level is too high or not closing the seat. you might want to take that carb apart and check to see if the float is stuck

 

[Chris1956]

Re: 1978 Mercury 900 (90 hp) outboard stalls out when you hit 25 mph

Actually, that is the backdrag jet. It does mean that the float is not maintaining the correct fuel level in the carb bowl. You likely need to clean the carbs, replace the gaskets, floats and inlet needle and seat. Also set the float height properly.

Rebuild the fuel pump for good measure. Maybe it was part of the problem as well.