115hp Mercury

Hi All !

My friend had 1970 mercury with 115hp , I went fishing with him another day . First the boat speed seem to go real fast . About a mile then it shut of itself , then he restart the engine next thing the boat can't speed at all .

every time he try the idle or speed it would kill the engine . Someone was mention to him that he may be lost the compression on one of the cylinder. And my question is how to get a compression back to 125 psi ?

What do i need to do to fix the compression problem ?

Thanks

Chris

Re: 115hp Mercury

Well with a questions like "what do i need to do to fix compression" you clearly have no clue about boat engines...or really any engine in general. SO assuming that is correct you should bring it to a boat mechanic. That is why no one has responded to your question.

But I will tell you a few reasons why you lost power...one could be compression which is a loss piston crown from detonation, ring failure, cylinder scuffing, or carbon build up. You can do a decarb if it's carbon build up . Most likely it's not that and if you don't have compression you need a full rebuild. It could also be you lost spark on a piston or two. This is what i would guess, it could be your startor, trigger, switch box(s), or coils.

This is where you're friend needs to go buy a OEM factor manual from e-bay and start reading to understand what i just wrote or bring it to a mechanic. GOOD LUCK!

Re: 115hp Mercury

sounds to me like its the switch box, they are 350$ new, or you can find them online for about 70$ used.

Re: 115hp Mercury

Chris, The issues could be fuel, compression, or even spark. The only way to figure it out is to remove the spark plugs, jumper the starter solenoid and test the compression on each cylinder. If they are 100PSI + and even, the motor is not too ill. Next is a spark test. Since that motor is a distributor igniton, check the spark plug leads for arcing to ground. Replace any wires that arc. Next clean up all three carbs and rebuild them with new gasket sets. Inspect the floats for deteriation. Replace all that have started to disolve.