No power

I have a 1972 IMP 21foot with a mercruser (ford) 302 and a 888 drive. it runs like a bat out of hell out of the water. when I put it in the water it seems like it only has 1/3 the power. I did a tune up and rebuilt the holly double pumper. I know nothing about out drives. could that be the problem? it goes into gears fine and the prop spins without making bad noises. Please help.

 

Out of the water, with no torque applied, it doesn't mean much that it revs up. Do a compression and leakdown test to start with. Also, check the timing and advance response.

 

Check to make sure the exhaust is not clogged. Back pressure from a clogged exhaust can really reduce power under load. Doing a leak down test is good idea too.

 

Are we firing on all cylinders ? If there is any starting difficulty when cold, could be the problem. It sounds like a fairly easy job for an experienced mechanic to troubleshoot, given it is an old engine from the days when things were pretty simple.

 

Welcome to the forum.

By the appropriate manual for the engine/drive and run through the diagnostics section in the beginning of the book. I doubt it's the exhaust and will suspect it's the distributor advance, since you've just rebuilt the carb. Distributor function easy enough to check while in the driveway, with some basic tools and some understanding. I'll bet on a hanging/stuck weight, broken advance spring, etc. being the actual issue. This is a common problem on older engines. It's just one of those places that doesn't see any maintenance and is out of sight, without some disassembly. The first thing to do is put a timing light on it and see if it's advancing properly.