[Solved!] New motor, first run... issue with.. ventilation?
Posted: Tue May 22, 2018 6:02 am
Old Landau pontoon. Swapped out an almost 23 year old 30hp 2-stroke for a brand new 40hp 4-stroke. Tohatsu with power trim/tilt
This boat has U-shaped pontoons filled with foam.
Motor mounts on a "transom pod" ... no center pontoon. Just a basically triangular... well you guys know what I mean...
We're on the Erie Canal. Speed limit generally 6mph, no wake. But we have access to a river and there are some undeveloped area where I can open it up a bit. So we launched yesterday to take it to the marina where our slip is, about a half hour boat ride.
Break-in for the motor says to keep it below 3,000 RPMs for the first 2 hours. Then below 4,000 until it has 10 hours on it. 1 to 2 minutes of full throttle permitted with 10 minutes between full throttle runs. I want to follow the break-in.
So we're on the canal headed for the marina. Motor sounds great. Very quiet. Running 6mph has it at about 600 RPM on the tach.
Our old 2-stroke... wide open... would give us about 12mph (this is all GPS) if we were lucky.
I advanced throttle on this one and at about 10 or 12 mph it starts... either cavitating or ventilating. I'm not totally sure which, but lots of air entrained. You can hear it happen. Here's the weird part though (to me)... the RPMs didn't run up when this happened. Couple times I heard it run up a bit. But I never got it over 2,000 RPMs.
The cav plate on this motor is where the old one was. I can not lower the motor on the transom. It's down as far as it goes.
I positioned the trust rod on this one such that the cav plate is not quite parallel to the bottom of the pontoons. By that I mean, when it's down-trimmed all the way, it is just slightly negative trimmed (tucked under... prop pointing very slightly down as opposed to being in a straight line with the line of the pontoons.) VERY slightly.
My wife likes to ride up front on one of the "fishing chairs" so I had weight on the bow.
It ALMOST seemed like it was sucking the back of the boat down and causing drag? Would that be why the RPMs didn't get over 2,000?
Here is what I want to try...
#1, put the thrust rod back in its lowest position so the motor has full range of trim. My transom is not straight vertical. It's angled. I had thought that letting the motor go that far negative would be bad. Maybe I was wrong. I had thought that letting it go that far negative would cause "plowing". Maybe I was wrong.
This motor also weighs 200 pounds where the old one was 100 pounds.
Appreciate any and all thoughts on this.
This boat has U-shaped pontoons filled with foam.
Motor mounts on a "transom pod" ... no center pontoon. Just a basically triangular... well you guys know what I mean...
We're on the Erie Canal. Speed limit generally 6mph, no wake. But we have access to a river and there are some undeveloped area where I can open it up a bit. So we launched yesterday to take it to the marina where our slip is, about a half hour boat ride.
Break-in for the motor says to keep it below 3,000 RPMs for the first 2 hours. Then below 4,000 until it has 10 hours on it. 1 to 2 minutes of full throttle permitted with 10 minutes between full throttle runs. I want to follow the break-in.
So we're on the canal headed for the marina. Motor sounds great. Very quiet. Running 6mph has it at about 600 RPM on the tach.
Our old 2-stroke... wide open... would give us about 12mph (this is all GPS) if we were lucky.
I advanced throttle on this one and at about 10 or 12 mph it starts... either cavitating or ventilating. I'm not totally sure which, but lots of air entrained. You can hear it happen. Here's the weird part though (to me)... the RPMs didn't run up when this happened. Couple times I heard it run up a bit. But I never got it over 2,000 RPMs.
The cav plate on this motor is where the old one was. I can not lower the motor on the transom. It's down as far as it goes.
I positioned the trust rod on this one such that the cav plate is not quite parallel to the bottom of the pontoons. By that I mean, when it's down-trimmed all the way, it is just slightly negative trimmed (tucked under... prop pointing very slightly down as opposed to being in a straight line with the line of the pontoons.) VERY slightly.
My wife likes to ride up front on one of the "fishing chairs" so I had weight on the bow.
It ALMOST seemed like it was sucking the back of the boat down and causing drag? Would that be why the RPMs didn't get over 2,000?
Here is what I want to try...
#1, put the thrust rod back in its lowest position so the motor has full range of trim. My transom is not straight vertical. It's angled. I had thought that letting the motor go that far negative would be bad. Maybe I was wrong. I had thought that letting it go that far negative would cause "plowing". Maybe I was wrong.
This motor also weighs 200 pounds where the old one was 100 pounds.
Appreciate any and all thoughts on this.