I have a friend of mine who just had to put in a new long block as the prior owner of his boat did not winterize. The motor is back in and all is put back together....here's the catch. The 4.3 is in a 18.5' Mariah open bow and he's running a 19P 3 blade Stiletto prop and he can only get about 4300RPM and is rather sluggish throughout the RPM range. The plugs, dist. cap and rotor, and fuel filters are all new and look to be in great shape. The motor runs ok and doesn't miss or sound "funny" but it just doesn't have a whole lot of power. My guess is the timing is not set properly or that the carb (2-barrel) has some issues. Could engine/drive alignment be part of it as well? Any other ideas?

check the ign timing.

Try a 17P 3 blade. I had a 21' Maxum with a 5.0L and didn't have any power with a 19P, so I always ran a 17Pwith 50MPH and 4800RPM. I don't know what the gear ratio was in the drive. As it is a new boat I would say it just has the wrong prop on it.

28Elim,
The boat is a few years old and the motor is new. I've been in plenty of boats that size and it should pop right out of the water and pull all the way up to top speed and top RPM without any hesitation as the hull/engine combo is light enough and powerful enough (should be!). I had a friend of mine with a 3.0L 4 cylinder who had more power and acceleration with the same size boat...that's what makes me hesitant that there is something wrong with the setup. Sounds like it could be a timing issue!

Thanks for the replies...keep them coming.

Dave: It sounds like a timing issue. I have a 18' donzi with a 4.3LX motor. When I first got it, it was sluggish and for a couple of months I thought that was the way it was. One day, it started to run on after the key was turned off and I knew the timming must be off. When I put the timing light on it, it was way off and I adjusted it to spec. What I could not beleive was the difference afterwards. the speed of the boat went from 42 mph to 48mph with a 19" pitch prop. Plus, the response and acceleration was so much different. Check that timming!

I have a little 17 runabout with an Alpha/3.0 4cyl running a 19' 3 blade, and it is under propped- A friend had the same setup and ran a 21' prop.

I think you need to look at engine timing, both at idle and at full advance. I would then check carb/fuel items.

Bulldog aka Ronnie