Re: New owner of a 89 Larson with a 3.0L Merc
If you have an OMC Cobra outdrive, then you have an OMC 3.0...... The 3.0 engine is not made by mercury or OMC -- its a Chevy engine actually -- the drive manufacturer simply customizes the engine to fit and propel their drive -- you'll find these in Volvo Penta and other brands of boat drives as well...
In a used boat, it's not uncommon to find (for example) a Mercruiser labeled flame arrestor on a boat with an OMC drive.... Used parts are cheaper sometimes -- as said above, the OMC 3.0 and merc 3.0 are essentially the same engine -- but it's preferable to post the problems you are having in the section marked for your brand of drive since what seems like an engine problem may actually be a drive problem and the people most familiar with those setups usually read that section....
That said, if you just had your drive rebuilt and your problem started at that point, I would agree with the above post -- suspect the drive.... OMC's are VERY touchy about their shims (as mentioned above) -- and need to be shimmed just right...
There are other things that can cause loss of power in the water too.... Fuel mixture wrong (running in the water -- in gear especially -- takes a lot more power then running on a hose), timing off, timing order wrong (this usually causes a rough idle regardless of if its in the water or not -- correct order is 1-3-4-2), water in the fuel, low compression, uneven compression (lowest compression should be at least 75% of the highest compression), burnt or otherwise damaged valves or seats, cylinder face crack (this usually results in water in the oil), fried gimbal bearing, etc......
If I were you, I'd have the place that rebuilt your drive test it to make sure it's right..
Next thing to check is the gimbal bearing -- make sure its installed correctly and turns smoothly
Next thing to check are the U-joints -- they too should be well lubed and move freely and smoothly -- if the shaft wants to stick straight out when the drive is removed from the boat -- thats bad
-- it should fall and point down as soon as you let go of it...
Next thing to check is the shift interrupt switch and the alignment of the shift cable... You did say the problem is in both forward and reverse, right? If its only in one direction, this is probably your cause....
Next thing to check is compression and/or leak down. You can get a compression tester from most autoparts stores.. Pull all the spark plugs and test each cylinder following the directions on or in the package the tester comes in. Some parts stores have these in their loaner tool programs too.
Hope this helps
