115 hp Mercury losing power.

[smhj]

It acts like it's running out of gas then clears up. It started end of season last year. I changed gas and the bulb this year also cleaned pick up screen in the gas tanks. I have 2 6ga tanks. I can sit at dock for 10 min WOT then go out and run around then slugs right down and stalls at times. Will start right up but real low idle then clears up. Forgot put a new filter on also. TIA

 

[jimmbo]

Which 115 is this? Inline six, 4 cylinder, 3 cylinder, or V6 Optimax?

 

[smhj]

Inline 6.

 

[444]

Rebuild the fuel pump? 6000rpm in neutral with no load consumes much less fuel than 6000rpm in gear under load.

 

[smhj]

No I haven't rebuilt the fuel pump. When it's under load or neutral it does the same thing. I had wide open for 10 minutes under load then it goes sluggish. I start feathering the throttle and ends up dying. Starting it again it can be full throttle and revs real low then start building up.

 

[smhj]

No I haven't done fuel pump. I can run it under load (wide open) for 15 or 5 minutes then it starts to die. Restart it and it won't stay started unless it's throttle is all the way down then she will finally start coming alive.Then it will happen again. When I think it blow carbon or whatever out of it it will start to die again. I also use the quicksilver additive in the gas.

 

[old evin]

iF YOU CHANGED THE PRIME BULB DID YOU CHANGE THE FUEL LINE? IF YOU USING THE GRAY ATTWOOD FUEL LINE IT HAS A PLASTIC LINER INSIDE OF IT AND WHEN YOU PUSH OLD FUEL HOSE ON TO THE PRIME BULB SOMETIMES THE LINER WILL BUNCH UP AND CAUSE A FUEL FLOW ISSUE. SO, IF YOU USED OLD LINE AND A NEW BULB PULL THE LINE OFF AND MAKE SURE IS ITS NOT RESTRICTED.

 

[smhj]

Update changed the gas connectors on both tanks put seafoam in gas runs them same. Bulb doesn't really get hard. I disconnected the fuel line from the motor and it gets hard. Could the fuel pump allow fuel to go by it? Like I said I can have it wide open in neutral and only rev at 1200 then it slowly go up to 3600. Does the same thing under load. It's a 79 serial # 5240946 can't find rebuild kit for fuel pump. Any ideas? TIA

 

[jimmbo]

Why do people insist on revving the engine in neutral????? WOT in neutral is even dumber, if the motor can survive it, it can be damaged.

Are the vents in the tanks open? Have you tried running with the fuel cap loose? You say the primer bulb never gets firm when connected to the engine? Have you looked at the engine, with the cowl off, to see if fuel is leaking or a line is bulging? A ruptured diaphram in the fuel pumpcan cause all sorts of issues. Pump kits should be available from iboats.

 

[smhj]

Revving in neutral is the only way it stays started until it acts normal. The only thing I saw was today where it is leaking fuel out of the bottom carb when I pump the bulb. Can't find the right part # with my serial # for the pump kit.

 

[jimmbo]

. The only thing I saw was today where it is leaking fuel out of the bottom carb when I pump the bulb. Can't find the right part # with my serial # for the pump kit.

Leaking fuel out of a brass orifice? Dirt in the float needle, misadjusted float setting, or a stuck float can cause that. Try tapping the fuel bowl moderately gently with a screwdriver handle, if the float is stuck that might free it. It did on my 115. Otherwise you are going to have to remove the fuel bowl covers. I remember doing that(30 yrs ago) without having to remove the carbs, but the front of the cowl support had to moved out of the way. My engine didn't have a choke system so once the support was out of the way I had a clear view of the carbs.

 

[smhj]

Update had a little help yesterday while looking for the problem. While pumping the bulb and watching fuel leaking out the bottom carb my helper had fuel dipping on his foot. Looks like the pump was also pushing gas thru the one of the vacuum lines. Ordered a gasket wish me luck.

 

[racerone]

Best to have a look at the fuel pump diaphragm.

 

[DJ_Allatoona]

Best to have a look at the fuel pump diaphragm.

Hey racerone, would you take a minute and look at the post I made at the top of this Mercury/Mariner page? It's called "Very Frustrated". I read your comments on this board and I'd be interested in the ideas of someone with your knowledge. Thanks.