Mercury Sportjet 120 Carb problem

[industriallift]

Mercury Sportjet 120 Carb problem

I have a Mercury Sportjet120. Recently rebuilt.I have fuel coming out of bottom carb up through the main nozzle and out the front of the carb at cranking speed and continues to about have throttle. Carb has been checked. Float and seat are working properly. Fuel pressure is correct.I had this problem prior to rebuild so it's not something that has occurred since rebuild.Any ideas would be appreciated.

 

[Barnacle_Bill]

Re: Mercury Sportjet 120 Carb problem

Re: Mercury Sportjet 120 Carb problem

Problem has just about got to be with the float or the needle and seat. Has the need and seat been replaced? Is the float adjusted properly? Also, if it is one of those metal hollow type floats, it may have some fuel inside it making it heavier. Had that problem with a 25hp merc.

 

[industriallift]

Re: Mercury Sportjet 120 Carb problem

Re: Mercury Sportjet 120 Carb problem

Took the needle and float out of the top carb an swapped it with the bottom carb. Seat is non replacable. Float is plactic. Floated both in a sink of water. Both float the same. cheack the seat with a flash light. It looks good. Also cranked the engine with the bowl off and hold up on the float. No fuel passing the needle.. This has got me stumped.

 

[dtrout]

Re: Mercury Sportjet 120 Carb problem

Re: Mercury Sportjet 120 Carb problem

I have the same problem with a 1994 sport-jet 90. all three carbs leak as you discribe. I found that according to the service manual they had the wrong floats insalled. I replaced them with the proper part and still have the leak. With the carb upside down the flaot drops and seasls the inlet. hold the carb in its proper position and apply fuel with a primer bulb and it leaks turn it upside down and apply pressure and it seals. Anybody have any thoughts? I have been owner an outboard shop for 25+ years and have never had a problem like this..buffalo@pa.net

 

[LargoDon]

Re: Mercury Sportjet 120 Carb problem

Re: Mercury Sportjet 120 Carb problem

I would check the carb vent tube (yellow hose) and especially the little 'T' and elbows for clogs. my carbs did exaclty the same thing and the vent was clogged up keeping the floats stuck in "air" and not floating in gas- which kept them open and caused gas to flood out of the carbs.