Mercury 125 hp problem

[stremo]

Hi guys hope someone can give me some help
I own a 125 hp merc mid 90s oil injected model
After inspecting the gearbox found out that the main pinion gear was missing teath so i went out on the hunt and found a gear box with the mid section plus the mounts my mounts where pretty much stuffed so i decided to pull the power head off which ive done many times and replace the complete bottom and keep my power head and cover so i did this and like every other time it started first pop so i took it out today started like usuall i was just giving it about 1/4 throttle and went to open it up and she took off then after 30 seconds i got this horrible pinging tapping sound backed of straight away sound went away so i tryed it again and just oppened it up all the way no sound but then it came back once i heard this sound it started losing power straight away i didnt even touch the power head just lifted straight off then back on would a lack off oil do this or does it sound like there is something in the crankcase but from about 1000rpm to 2500rpm its fine if it was something terminal i think you would here it straight away on idle compression is also fine i striiped down power head about six months ago to fix a bodgy mechanics job dont really want to do this again anyhelp would be great ive never had any problem like this before prior to the repairs
Cheers Tim

 

[hamit59]

Re: Mercury 125 hp problem

I think I would run it on a remote tank of premix 50:1 see if it's still hear the noise.
You may be running lean on oil. As for the bearings in your motor who knows for sure. Auto oilers are nice but they will go out or stop up and when they do most folks don't find it until it's too late. I premix it's easy and I know I have oil

reply back tell us what you find

 

[Ed R]

Re: Mercury 125 hp problem

sounds like you lost a pistion, ?? check compression.

 

[stremo]

Re: Mercury 125 hp problem

Hi guys i checked compression on all cylinders all are fine also i took all the old fuel out plus i took off all carbys and blew them out changed filter also changed spark plugs and leads all carbys are getting fuel but i did notice on cylinder 2,3,4 the spark plugs seems with wet with oil,fuel 1 is fine it seems to be burning fuel on that cylinder would a weak spark do this but i dont get how it idles fine and revs up fine when idleing only when i get on the plane above 3000rpm then it loses power then i get this noise really got me confused any suggestions

 

[stremo]

Re: Mercury 125 hp problem

It seems to be using the 2stroke but i will try and run some in the fuel tank anythings worthe a try can i leave the oil tank on and just run the oil in the tank??Motor was stripped down about 6 months ago all bearings where good

 

[CharlieB]

Re: Mercury 125 hp problem

Which water pump are you using?

Did you install a NEW impeller?

You may be running cool enough at lower speeds but as soon as you start to lean on it it is beginning to heat rapidly, to the point it is making noise, you get out of it and it cools.