Low Compression in top cylinder

My 82 Mercury 50 only has 40 lbs compression in the top cylinder and 125 in the other three. The motor has only enough power to troll slowly along and when I try to give it more gas it stalls out and kills the battery. Is the lack of compression in the top cylinder giving me all the problems? What should I do here? Engine will start and idle but is not idling smoothly. Wondering what I can do to try to get the power back in this engine.

Re: Low Compression in top cylinder

Sorry but it wont run long like that. You need to find out why number one is so low. Remove the head and take a look at the cylinder walls. Any deep cuts or worn slots in the wall= new powerhead and money . If the pug in number one is extra clean compared to the others it means you are pumping water into the cylinder which also means a major issue. How much do you think the engine was worth before it started giving this trouble?

Re: Low Compression in top cylinder

How long has it been like this ? if not long try to decarb.....
good luck
arcrat

Re: Low Compression in top cylinder

1. A 4-cyl Merc doesn't have a cylinder head. The cover at the back is only a cover for the block's water passages.

2. Decarb ain't gonna bring back a cyl with only 40 psi. The powerhead needs a rebuild.

If you you wanna try and see how much damage there is before you tear it all apart, remove the transfer port cover on the intake side of the motor (Stbd side), and look in thru the intake ports. You'll be able to see the exhaust side of the cylinder and most times that's where the worst of the damage will be. Look for signs of cylinder scoring.

You can also pull the exhaust manifold covers and look in thru the exhaust ports. Watch out, though, if the bolts don't turn easily, they're probably stuck and you'll need some heat applied to get them loose without breaking.

You can try the decarbonization routine if you like, it's not gonna hurt anything. Just don't get your hopes up too high!

Here's info on doing the decarb:

http://forums.iboats.com/showthread.php?t=158076&highlight=seafoam

HTH & G'luck..........ed