77 Merc 1400 140hp very low power and does not like to idle

[AaronIROCZ]

I have a 1977 mercury 140 hp outboard inline 6 that all of a sudden lost power and seems like to have picked up a vibration, just seems to shake a bit more than normal. I had the carbs rebuilt last year and had the timing adjusted, and a new diaphragm in the fuel pump as well, after that it ran great last year. I put it away last year and drained all of the gas out of the carbs and put fuel stabilizer in the tank. When I got it out this year it ran great at first then started to bog down and would not climb any higher that 2500 rpms, and also would stall quite a bit when trying to take off at part throttle or full throttle. I noticed fuel running out of the carbs while it was running so I tore the carbs apart again and lowered the float level and cleaned them all up again. I took it back to the lake and the engine ran great again, just does not like to run at low rpms, just stalls after about 2 min "trolling" around, it mostly starts right back up after it stalls. We sat at the beach for a few hours and had to go pick u a friend at the dock and while on the way back the engine ran awsome, got 40 mph out of it, best it has ever did!!! I slowed down as I got closer to the docks and then I noticed the rpms falling pretty fast from 3000 rpm down to 12-1500 rpm and then noticed a little shaking coming from the motor. I double checked for the tell tale stream of water to make sure the water was flowing and it was. I limped it back to the beach to pick up the rest of the friends and came back to the dock and pulled it out of the lake and checked the plugs Champion L76v and noticed the top one looked a little grey compared to the others, the others were tanish to black. I looked inside the cylinders and all the pistons looked fine, no holes or broken sections. I plan on changing the plugs out to maybe NGK's???? Any other ideas I should try??? Sorry for the novel just trying to explain how everything happened.

 

[achris]

Re: 77 Merc 1400 140hp very low power and does not like to idle

A gray looking plug is a sign of water getting into the cylinder, and that was my first thought even before you mentioned the plug... When were the exhaust cover gaskets and lower crankcase seal last changed out? For those engines it should be done about every 5-7 years.... and it's a pain.

Chris..........

 

[AaronIROCZ]

Re: 77 Merc 1400 140hp very low power and does not like to idle

As far as I know it has never been changed, at least I have not done it in the 2 years I have owned it. How hard would it be to replace the gaskets. I can work on cars all day long but when it comes to these outboards they seem like a different animal to me. Should I get a complete gasket kit for the motor??

 

[Chris1956]

Re: 77 Merc 1400 140hp very low power and does not like to idle

Aaron, First get the correct year on that motor. I do not think Merc made a 140HP in 1977. Not that it matters too much with parts, since they are all pretty close.

To change the exhaust gaskets requires that you remove the gearcase and the powerhead. To remove the powerhead, you also need to remove the cowling supports, starter, distributor, and disconnect much of the wiring. Put the block on the bench and use some heat and penetrating oil, as well as an impact driver to remove the bolts on the exhaust cover and inner exhaust cover. They like to break so be careful.

 

[AaronIROCZ]

Re: 77 Merc 1400 140hp very low power and does not like to idle

It does say 1978 on the motor and the boat is a 1977 Sea Ray, so it would be a 1978. Do you think it could be done in a weekend as long as no other problems exist?? I am looking to sell this boat this fall or next spring and need to get the engine running good in order to upgrade boats. By thw way thanks for your help!!!

 

[Chris1956]

Re: 77 Merc 1400 140hp very low power and does not like to idle

OK if the motor is a 1978, it will be labeled as a 1400. It is identical to a '77 Merc 1500.

You should not need a whole weekend to replace the exhaust gaskets, unless you break some bolts...

 

[achris]

Re: 77 Merc 1400 140hp very low power and does not like to idle

OK if the motor is a 1978, it will be labeled as a 1400. It is identical to a '77 Merc 1500.

You should not need a whole weekend to replace the exhaust gaskets, unless you break some bolts...

And you will break bolts....