Mercury 150 runs rough

[reelchief]

So i was on my way to a dive site and my low oil alarm sounded. instead of stopping the boat and adding oil i decided to do it on the move and ended up spilling oil down the front of the engine block. I know dumb mistake. so after that the motor is noticably slugish. after completeing the dive i am having a hard time gettin the motor to start. it will start and idle but when i go to put it in gear and go it dies. i finally get it to limp home and i end up rebuilding carbs and now the boat idles like a champ but when i ran it the motor did great for about 20 minutes then died out and went back to running rough. now i am thinking fuel pump. the spark plugs looked good and the compression checked out. does anyone have another idea of what it could be

 

[SparkieBoat]

Re: Mercury 150 runs rough

check you spark on each cylinder with a spark gap tester..check compression..check all fuel lines/connections and filters...if cleaning the carbs fixed it for a short time maybe you got more trash in carbs again..just a guess..check your timing and linkages..i am not sure what spilling oil would have done to harm your motor..unless maybe it got into a wire connection...

 

[reelchief]

Re: Mercury 150 runs rough

well turns out the gauge i used for the comp test is bad so i redid the test and one of the cylinders is dead. when i tore the head off i saw black oil in the cylinder and the cylinder walls are rough. i was also able to slide a spacer between the piston and the wall so i now the rings are done. does anyone have advice on what to do next. i figure i have 3 options 1. smooth the cylinder and replace the rings 2. bore all the cylinders and put in the .015 rings and new pistons or buy a new motor. please give me some feedback on what i should do next

 

[SparkieBoat]

Re: Mercury 150 runs rough

what year is the motor??? I would go find myself a good used motor and either keep or sell that one for parts..but I do not do engine rebuilds because there are too many good used motors out there at less cost than rebuilding. some people like to rebuild motors so it depends on what type of person you are..I am all about the quickest way to get going again for the least money/effort..

 

[reelchief]

Re: Mercury 150 runs rough

So i broke it down and found that the piston fused with the rings at one spot. I honed out the cylinder and smoothed it out with a few grooves that i couldnt get out. its still within specs. I just ordered and new piston and rings for that one cylinder. I will post back what the new pressure readings are when i put the new piston in. The reason i dont want to buy another used motor is because i dont want to deal with a new set of issues. I am also leaving for afghanistan in 2 months so i jsut need something to get me to the dive sites and short fishing trips. I'm really hoping my wife will let me buy a new 4 stroke. its either goign to be new motor or bore the cylinder out .015 on all the cylinder. Has anyone done that and what was the outcome? Did the motor perform better bored out or did it cause more problems? just want to know.

 

[SparkieBoat]

Re: Mercury 150 runs rough

you need to figure out why that cylinder piston was damaged...My guess is a clogged carb...I have decided to stay with the Carbbed motors as opposed to EFI/HPDI, because I can trouble shoot/fix them myself..I have taken the time to learn what I need to know to test a used motor before buying, so I am not fearful of used motor purchases.

 

[j_martin]

Re: Mercury 150 runs rough

Like sparkie said. You roasted one, now find out why or you'll just roast it again.

If the bore is reasonable, a new piston will put you back in business.

my 02
John

 

[reelchief]

Re: Mercury 150 runs rough

The cost of boring a motor is not an issue. i have access to a machine shop so any work i need done is no problem. Wat i am wondering is what people who have bored out their engine think about its perforance after it was reassembled.

 

[reelchief]

Re: Mercury 150 runs rough

So i got the new piston and rings in. I honed out the cylinder to make it as smooth as possible. there is still some minor grooves but deffianly alot better then before. I put the motor back together and did a compression test and got 125 on the 5 cylinders and 90 on the one i just redid. I am assuming this is because of the small grooves still in the cylinder. well i guess 90 is better then 0. I still think i need to strip down the block and have it bored out and install oversize piston and rings. I would like to talk to someone who have bored out and rebuilt a motor to find out soem common mistakes and things that i should make sure i do/replace.