Vibration under partial throttle?

Took my Ski Tique out for its first big day of my ownership yesterday. I had some observations on its performance that I needed clarified. When I take it out alone the boat flies, but if I get two or three more people in the boat it becomes very slow when accelerating, and has a vibration that rattles the windshield when I'm accelerating up to speed, it goes away mostly at higher speed. Plus, if I'm towing a tube with a few people in the boat the prop will make a cavitating noise and the motor will have a surging sensation when turning. With a few people in the boat and I try to accelerate out of a corner it doesn't matter how hard I push the throttle, the motor has no real response and just takes a while to get up to speed. Is this just a weight issue? Another thing I noticed was at part throttle just cruising I can feel the motor surging a bit...Any ideas? (I know its a lot of things at once)

Adam, Keep in mind that the Tique is a small boat and even the addition of 1 person will make a difference. Also, there are lots of harmonics at certain speeds. The hulls can act as a giant speaker. Do check the engine as it sounds like you do have issues. Check the driveline too as Eric stated. A cupped prop will sometimes help will cavitation but what you are experiencing on turns may be normal. I had my 77 Tique out Saturday and they do hum quite a bit!!

one small ding will do it, that ding may have bent the blade a touch which can be naked to the eye. a good example to compare things to is a tire on your car, it is spinning a tenth slower and you wouldnt think those little lead weights would make a differeence but they do.
Your prop is spinning engine speed or close to it and if not perfect you will get a intermittant vibration. Send it to the prop shop and see what they say, I too was a victom of hitting some sand and thought that little ding wouldnt hurt a thing and behold the prop was bent along with the shaft, so dont rule out the prop

could pulling a heavy load from the skylon make the prop bite at weird angles causing problems...?? just a thought I had

With a load it acts a lot differently. With a few people in the boat and towing a tube, when you take a turn sometimes it sounds like the prop is cavitating and there's a surging feeling. With a few people in the boat it just acts different all around. It becomes very un responsive. If I try to power out of a turn it feels like it only has like 30hp, and the motor wont put out any power no matter how hard I open the throttle, but this is along with that cavitation noise so I think it might be the prop. I have a whole list of things I'm going to check starting with the plugs, timing, everything in between and ending at having the prop checked.

This is my first boat, however I have driven many other ski boats with V-8's and not experienced what I have with mine. The weight suggestion is well taken, I did learn my lesson with that. I still will be going through everything though. I have learned a lot from this site so far and will be making sure everything is perfect in the driveline.

Adam, Good luck with checking the engine and driveline. Hope you find something obvious and simple. Keep in mind that the "back ring" is a lifting ring and not really designed to pull with. There has been some discussions on it in other threads.

acpskitique- What size/ pitch prop are you running? An incorrectly sized/ pitched prop could explain the cavitation issues.
I'd suggest having the prop checked and replacing the strut bushing (cutlass bearing?).

Also, how are your stringers at the rear mounts (tranny mounts)? Are the rear mounts tight? If for any reason they are loose or your stringers are rotted, then you could be binding up in the turns. When going straight that would not be noticable. Just another thing to check on.

Stringers, sound right to me. Have a 78 Tique, with wood stringer you have to check them often. Not like to stringers and engine mounts of today. Check for stripped lags or cracks.