Correct motor height and weight

jakepart

Cadet
Joined
Jan 26, 2014
Messages
9
Okay guys, its been a while since I've needed info but here I am again. I recently purchased a '94 Stratos 284 dual console bass boat. It has a '94 Evinrude 120hp. I recently fished a tournament and had 2 days worth of practice prior to. I ran through 2 tanks of fuel, which I thought was a lot considering my buddy running a 115hp on a nitro only ran through one and we pretty much fished and ran the lake the same amount. I originally thought that my motor was sitting too low since the water comes almost to the where the upper part of the motor begins to widen from the shaft when trimmed all the way down and I read that having your motor too low would produce a lot of drag and burn fuel faster. So I was able to check it over the weekend and while running at almost WOT it appeared the cavitation plate was a little high out of the water leading me to believe the motor is too high. I don't feel that I can get up on plane as well as I should but if I trim up more, I'll start sucking air. My stern seems as if it sits too low as if its too heavy but there is nothing out of the ordinary that would cause it to be overweight. I am lost and looking for some input. The boat is rated for up to a 150hp so I don't think the motor is too big. Let me know if there is any other info that would be helpful.

Thanks,

Jake
 

jbcurt00

Moderator
Staff member
Joined
Oct 25, 2011
Messages
24,829
What year 115hp is your buddy running, on how long a bass boat, and are you positive your motor is running 100% as it should?

If your hitting the upper rpm limit of the motor at WOT, I dont know what that is for a 94 120hp Evinrude, but the specs are available online, you might have to look around to find it, you are probably running the correct prop.

I'd start w running right: timing, plugs, wires, impeller and etc

Then confirm you are running the correct prop size/pitch to hit rom range for WOT.

That plate should be just above/below water when running, so it sounds to me like its height is correct, if the motor wont trim and do much, it does sound stern heavy, which might be water weight..

Its a 20yr old boat, it might be heavier then it was when it left the Stratos factory. Thats a whole different set of problems.
 

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
If it seems heavy in the stern check if the foam under the floor has absorbed water.
If the boat has been refurbished sometimes the hull can be distorted or uneven.
How long to go from 0 to planing speed?
If you have venting issues the motor may be too high though there are props that resist venting.
What is the prop size (probably under the prop nut) wot rpm and gps speed?
Is the bottom clean and smooth?
 

jakepart

Cadet
Joined
Jan 26, 2014
Messages
9
Thanks for the quick replies. My buddy has a 99 Nitro 17.5ft and I believe the motor is a 97 Merc. I know there are differences but was just using it as a comparison. It usually takes about 5-7 seconds to get on plane, not very long. I tried locating the prop size and all the info but didn't see anything directly on it so I guess I will have to pull it to get the info for sure. It is a 3 blade stainless but I don't know the pitch. It does trim pretty well up to a certain point while running then stops as if it can't handle the pressure being put on it. Sitting, it will trim all the way up with no problem. WOT rpm is right at 5000 if not a little more. I had it up to 50 on gps with about 1/4 tank and no gear by myself. During the tourney, best I got was 42, 2 people all our gear and a full tank. Is there any real easy way to see if the foam as has been water logged?? I thought that at first, but not sure how to really check or even know where to begin to try and fix it. Everything is fiberglass and sure hate to cut into it. Maybe it is running fine and I am just expecting too much out of it. I am also comparing it to my last rig that was only a 15 1/2 ft tidecraft with a 75hp on it and I was running 40mph also. Just figured a bigger motor should run a little faster. I know the boat weighs more, but who knows...... trying to figure it out.
 

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
My info indicates the 120 is rated at 5500 rpm so at 5000 your not even in the max hp range.
I wouldn't get carried away but I think an rpm closer to 5500 would be more productive.
At wot your motor will burn at least 15 gph.
If your hole shot is around 5 sec. it's not likely you have wet foam.
Some times if its water logged if you store it with the bow up and the plug out you may have a constant drip.
Is the bottom clean and smooth?No paint?
If your not getting full trim then you may have too much boat in the water especially with a full load.
You may be able to gain some rpm just by maximizing trim.
I checked todays Etec 115 On 4 Bass boats 3 glass 18 footers1400 dry weight, averaged about43-44 mph.
with ss props 17" rpm about 5700.
One al 17 ft 1017 dry weight 20"ss prop 52 @ 5725.
These very efficient direct injection motors averaged about 10 gph at wot.
Unfortunately your 21 year old "oldtec" will be lucky to make the 15 gph I suggested.
Sometimes if a fuel pump diaphram gets a hole in it it will leak fuel into the motor increasing fuel use.
 
Last edited:

jakepart

Cadet
Joined
Jan 26, 2014
Messages
9
I suppose based on your test results, I am not too far off of spec other than max rpm's. Since i know for sure that I cannot trim up all the way, my trim motor/pump may be going bad. I did change the plugs and clean the carbs, so maybe it just needs a full tune up and get the timing checked. It does shake a bit but isn't that expected for an older 2 stroke??
 
Top