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1983 2.5L Mid Range Power

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kountzelightdiesel

Contributing Member
I have a 1983 OMC 2.5L sterndrive the boat was a wreck when I got it set up for too many years outside after rebuilding the boat I ran it for one ski season. I have a complaint but not serious enough to do anything about till I'm getting ready for this season.

I have not been into the carb yet and it appears to have original fuel pump I tuned it up before last season.

Ok the problem the hole shot from 120 hp should be a little faster. On plane at WOT is 4400 trimmed down all the way up it will run a little over 4600 so prop pitch should be right where I need to be. At idle if you hit it the engine will rev to around 3000 until the boat is completely on plane.

Is there anyway to increase midrange power on these little engines without killing the top end? And any ideas on how to tell if thats just how it is or if it is low power? Projects this season will be to convert to elec. ign. and rebuild the carb. What about the mech. advance in the distributor? Any thoughts will be appreciated.

Thanks Jeff
 
first and foremost you should never ever run the stringer drive anywhere but fully down.

I'm surprised you have any ball gears left.

What size boat is this in ? Oh keep running this old piece of iron at wot and maybe you will get another year maybe less out of it.

Want a real ski boat get a outboard.

Only way to get more out of this boat is drop in a 3.0 / 140 direct changeout motor.

Good luck
 
He probably has selectrim.


Stainless prop- a Raker with vent holes can work well to lift the bow if a boat is bow heavy
Losing any excess weight in the boat
checking advance weights in the distributor a few suggestions

elec. ign will yield no performance gains - just a maintenance benefit
 
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Yes it is selectrim. I was thinking about the mech. adv. the springs are intact and the weights are free. Can those springs loose their tension and open too early? I used to deal with this some with hot rods but mostly that was missing or broken springs.

Its in a 16.5 ft. four winns When I reglassed the floor and transom I used same thickness material and plywood. so theretically it should weight the same as original.
The boat will run somewhere around 33 mph which is plenty of top end so I would rather not change prop pitch. I'm not familiar with a Raker vent holes = lighter faster to rev? As far as the elec. ign. I was thinking more accurate timing worn point cam lobe.
 
you checked compression ? I had a 120 85' in my 19' it was a dog, motor went cause of my stupidity, so i got my hands on a 140. It's a different boat with that extra 20 hp.

There is nothing you can do with it maybe put smart tabs on it, but i'm surprised you get only 33 in a 16 footer, maybe water in the hull, something is weighing you down ?

Wot is 4200-4600 so you cant go down in pitch even if you wanted to. You could try going up in pitch 2 degrees, will give you more speed get you to 35 maybe.

Thats it !
 
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