kbrown5897
Recruit
- Joined
- Apr 13, 2012
- Messages
- 3
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Advice needed!!
The motor was originally mounted in the very top hole, placing the motor the furthest in the water as possible. I moved it up one at a time, now being one the 3rd hole down, one hole from it being mounted at the highest spot (4 hole mounts). My 1990 16.5 ft boat has a 90 hp evinrude VRO on it (which is max) with a 13 3/4 x 15 pitch prop. It originally before I moved it would reach 5500 rpms and about 35 mph which the 5500 I understand is right near the max rpms for that motor. I was having real problems trimming the motor up at all without bouncing all over (porpoising). I also thought that boat should be going a little faster than that and was told that a 15 pitch prop on that boat should be spinning 6500 to 7000 rpms. Compression is about 110 or so on all cylinders.
After I moved it the first hole up, I couldn't really notice a huge difference. The rpms seemed to stay right at 5500, but I could trim it at least some...getting another 100 or so. Porpoising maybe wasn't as bad.
After I tried another hole putting the motor up even higher, I took it out and noticed that it would still only hit 5500 rpms, but it seemed as if it would get up to 4500 and 5000 rpms quite a bit quicker and with a little less effort on the throttle. I hit 5500 rpms and was about only 3/4 throttle. The last 1/4 of it didn't change the tach or didn't have any effect on motor. I looked back and took a picture of the cav plate, not sure if I was fully on plane...definitely wasn't wide open. Water seemed to spray to the left and right of the motor, probably from hitting that cavitation plate??
View attachment 144471
Any opinions on what could be going on? Could it be hitting that 5500 rpms and governing..not allowing it to go any higher?? I would of thought moving it up as high as I did would of raised the rpms some... Should I just try a 17 pitch prop and see what happens? Could the prop just have some issues?
Any help appreciated. Thanks!!
Advice needed!!
The motor was originally mounted in the very top hole, placing the motor the furthest in the water as possible. I moved it up one at a time, now being one the 3rd hole down, one hole from it being mounted at the highest spot (4 hole mounts). My 1990 16.5 ft boat has a 90 hp evinrude VRO on it (which is max) with a 13 3/4 x 15 pitch prop. It originally before I moved it would reach 5500 rpms and about 35 mph which the 5500 I understand is right near the max rpms for that motor. I was having real problems trimming the motor up at all without bouncing all over (porpoising). I also thought that boat should be going a little faster than that and was told that a 15 pitch prop on that boat should be spinning 6500 to 7000 rpms. Compression is about 110 or so on all cylinders.
After I moved it the first hole up, I couldn't really notice a huge difference. The rpms seemed to stay right at 5500, but I could trim it at least some...getting another 100 or so. Porpoising maybe wasn't as bad.
After I tried another hole putting the motor up even higher, I took it out and noticed that it would still only hit 5500 rpms, but it seemed as if it would get up to 4500 and 5000 rpms quite a bit quicker and with a little less effort on the throttle. I hit 5500 rpms and was about only 3/4 throttle. The last 1/4 of it didn't change the tach or didn't have any effect on motor. I looked back and took a picture of the cav plate, not sure if I was fully on plane...definitely wasn't wide open. Water seemed to spray to the left and right of the motor, probably from hitting that cavitation plate??
View attachment 144471
Any opinions on what could be going on? Could it be hitting that 5500 rpms and governing..not allowing it to go any higher?? I would of thought moving it up as high as I did would of raised the rpms some... Should I just try a 17 pitch prop and see what happens? Could the prop just have some issues?
Any help appreciated. Thanks!!