Boat Speed Question

cary00silve

Seaman
Joined
Jan 21, 2007
Messages
72
I just got a 1956 Evinrude 15hp motor running and took it out for a test run yesterday evening. The boat is a 14x40 flat bottom, and weighs around 200lbs. The total load in the boat including motor, gear and people was around 500 lbs, for a total weight of 700 lbs. According to my GPS, the top speed was around 12 mph. Does this sound about right? I was expecting a little more out of the motor. Also, I adjusted the fuel mixture for top speed, and adjusted the trim. The boat ran fastest with the trim at the highest setting. I had my wife on the bow, and the fuel and battery at the stern with me.
 

Chinewalker

Fleet Admiral
Joined
Aug 19, 2001
Messages
8,902
Re: Boat Speed Question

Is your motor running on both cylinders? I would expect closer to 20mph. Is the boat even planing off?
- Scott
 

cary00silve

Seaman
Joined
Jan 21, 2007
Messages
72
Re: Boat Speed Question

The boat doesn't seem to be planing off to me, but I'm not sure. I think it's firing on both cylinders because it runs smoothly and idles smoothly but it doesn't seem to rev out as high as my 5 hp. Would distributing more weight to the front make it plane out better? What trim setting should I put the motor on?
 

tashasdaddy

Honorary Moderator Emeritus
Joined
Nov 11, 2005
Messages
51,019
Re: Boat Speed Question

i had a 55 15 you should get atleast 20mph. check spark and compression, is the shaft length right for the boat?
 

Chinewalker

Fleet Admiral
Joined
Aug 19, 2001
Messages
8,902
Re: Boat Speed Question

Simply remove and ground one of the plug wires. If motor runs as it did before - the removed wire wasn't working. If it doesn't start at all, then you know where you're at...
- Scott
 

cary00silve

Seaman
Joined
Jan 21, 2007
Messages
72
Re: Boat Speed Question

I think I solved the problem... A few weeks back, I bent the flywheel when removing it (lesson learned, I now own a harmonic balancer puller). I didn't notice it was bent until I started the motor. When I did, the flywheel made contact with the magneto and it bent the aluminum arm that connects the tiller handle gears to the ignition advance system. This resulted in the throttle not opening all of the way. I bent the arm back to where it should be, and hopefully that will fix things. The spark is good on both cylinders (all new ignition), and the compression reads 75 on both cylinders. Hopefully I can test the motor out tonight and see if this fixed the problem. Is there anything else I should check before heading to the lake?
 

larky

Petty Officer 1st Class
Joined
Aug 23, 2006
Messages
300
Re: Boat Speed Question

the only other thing that comes to mind is the prop. is it the correct pitch and diameter for this application?
 

cary00silve

Seaman
Joined
Jan 21, 2007
Messages
72
Re: Boat Speed Question

I'm not sure what the pitch is on the prop. Is there a way to measure it?
 

cary00silve

Seaman
Joined
Jan 21, 2007
Messages
72
Re: Boat Speed Question

I just took the boat out this afternoon, and it topped out at 16mph. However, it would only run for about a minute or so and then the speed would drop significantly and sometimes shut off. I checked the water jackets, and they were cool so it wasn't overheating. I also checked the tank and it had good pressure with no leaks. I figured it must be the filter in the carburetor float bowl. So, when I got home I took the carb of and removed the float bowl and the filter. When I removed the filter, is was about 30% blocked by some black dirt. I cleaned it out and got everything back together for another test. Is there anything else I should check, or is that pretty much it? Thanks for all of the help!
 
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