1967 Johnson 40hp performance question

This is an awesome forum! Glad I found it.

On to the motor: The performance has deteriorated over the years (as you would expect). It's on 14' Glastron runabout. We used to waterski behind it in the 80's (it's been in the family for a while) but I haven't used it in about 4 years now as it was having a hard time pulling a 3 person tube. Back in the 80's it would run on plane at an indicated 26mph and sound pretty strong. I took it home from the cottage thinking I was just going to sell it. I cleaned the carb, found an air leak in the plug at the top of carb, sealed it and now it idles better than it ever did! Go figure...now I'm wondering if I should fix up the boat and keep it. I still have to test it on the lake. The lower end needs new seals, that's for sure. What should the compression be? Where would I "plug in" to vacuum test the block to ensure the crank seals are good? Is it big $ to rebuild the top end? Any thoughts/comments would be appreciated.

Re: 1967 Johnson 40hp performance question

compression i would want to see atleast 100 psi, but more important is that they are within 10% of each other.

read this http://forums.iboats.com/showthread.php?t=299680

also doing a decarb, would never hurt it, probably has never been done.

Decarb, take a can of seafoam put 3/4 of it in the gas tank, with only 1 gallon of premixed gas. put the rest in a spray bottle. start the engine, and let it come up to temperature. then remove plugs, and them some real good shot of seafoam into the cylinders, replace plugs, let sit 15 minutes. restart, and spray the rest of the seafoam into the carbs, so the the motor almost stalls, wait and repeat until the seafoam is gone.then take for a wide open spin. then put in new plugs, ad premixed gas to the tank, and take it for a wide open throttle spin. it is going to smoke like a house on fire, during this process.

afterwards compression.recheck