cavitation issue

Hello everyone, Im brand new to this site and owner of a 1986 procraft 1750v with a Force 150 (1991 i think) my question is this....i put the boat in the water for the first time yesterday and discovered a few gremllins......#1 an alarm went off in my throttle control after about 15 minutes of running time at idle ( it also did this when I hooked it up to a hose at home) is it an overheat alarm? its pissin water #2 , when cruising half throttle and boat plained off its cavitating big time noticed the top of prop is only 8" below bottom of boat what should the proper depth below boat be? #3 when you grab the bottom of the motor (prop,lower unit) I can move the motor out and in(back and forth) about 2 inches, does this mean the mounts are bad in the motor and lower unit thanks in advance

That's an overheat alarm.
If the motor and the transom are moving ANY don't run the boat.It can rip it off the transom.It should be rock hard and not wiggle at all.Is there a capacity sticker on the boat that tells how big a motor should fit on the boat?
Is it just the motor moving?
Sounds like someone has put too big a motor on a small boat.
Look at this site.It explains transom and cavitation plate heights http://www.onlineoutboards.com

If your alarm is going off at idle and on the hose, I would look at the spark plugs after a short run on the hose. You may have a blown head gasket. See if you have any water drops on a plug, and turn the motor over by hand and see if there is any noticable vapor coming from any one cylinder. A compression test would be next.

Then a new water pump. Last run with out the thermostat. First with the cover of the Thermostat off to check for real flow-(it should come out of there like a garden hose), then together and see how the water flow looks from behind.

I think your water temp and cavitation are two different problems.

Those motor mounts did give out and cause the engine to flop around dangerously. So first do the bottom mounts then try the cavitation issue again. It may be with the engine pointing wrong your plowing the front and lifting the back. When correctly mounted, the engines cavitation plate should be even or slightly lower than the bottom of the boat- use a straight edge, and watch the hull for a deformity known as "cupped". Where the bottom is not flat ahead of the engine but dished inward. There is no easy fix for that. Hope this helps

well thanks for all of your replies, I will start doing a process of elimination on this stuff, I did reright some of my findings yesterday but it didnt make it on the list for some reason. I used a straight edge on the bottom of the boat to recheck the prop depth...what I found was the centerline of the prop is 1 inch below the bottom of the boat that seems a little to shallow to me. where is a good place to find the ruber mounts that go on the bottom section about half way up? it seems it is removable through a cover plate. I guess this will stop my motor movement. I called a boat place here local and asked them about my overheat alarm,they said they would check the waterpump and replace it for $260, I said cant we check the thermostats first, they said its not usually the problem, but its alot cheaper to check it first i would think.

Change the impeller yourself.It costs about $20 If it's been ran for any length of time without water it needs to be done.If it's old then change it.
The cavitation plate should be even with the bottom of the boat.Block up a 3ft ruler under the center of the boat and lower the motor till it's staright up and down.See where it hits the plate.
Take a pic and post it.
The mounts don't usually go bad.Take a video of the wiggle and post it.
Taking the thermostat out could cost a lot more.It might strip the screws or break off in the head.
Then it will cost way more to fix the head.
Just change the impeller and save yourself $$$

Hey William, Well Ive started to go down this list and have come across a problem after step two.....step one was easy, i removed the lower unit and took a look at the impeller, nothing bad there I even took it to the boat shop and he said it looks good. it has me baffeled though, #2while I had the lower unit down and put the pump back together I figured I would hook the hose up and turn the prop to see what happens.....well I turned the prop by hand and it would burp water out for every turn of propeller the top of the pump just like I thought it should, just short of a flood though by hand turning. So I put it back together....started the motor up with the hose and .........gues what I cant get any water out of the pisser :-( so the next was #3 uncover the t-stat,,,, which by the way there is none suprise.I started it and there was no water coming out of the t-stat hole...hmmmm this cant be good, so I went back to step #1 remove the lower unit again 3rd time...I looked up in the unit thinking maybe the connection wasnt good at the top of the pump to the pipe, but it was good, so now im really stumped. why dosent water come out of the t-stat whole when runing? I blew air up in the pipe and I got plenty of air out the t-stat whole but no water

You do any thing I suggested? The answers are there.
If the impeller has ANY bends or set in the blades it might not pump enough water.Pics of the impeller?
Since it's off replace it.$15
The bottom of the boat and the cavitation plate should be even when the motor is straight up and down.
Don't worry about the prop shaft.THe shaft moves when you trim the motor.
You have a Jack plate on the transom?
The motor missing the exhaust snout?Pics?

Hey Jerry, Yes I have been trying to figure this stuff out, you have very good advice. This boat motor thing is new to me, im a car motor guy so I try to compare between the two........which dosent work,I went to that web site for transom measuring vs. shaft length and it appears my transom measures 22" and the plate to bottom is 24" and looking at the chart it puts me at the min. shaft length. I had a friend come over and look at the boat and he noticed I had pit marks in the prop (actually alot of them) then he noticed the blades were bent, he said those pit marks were caused by serious cavitation(heat stress) so I need a new prop......as far as pics to you I havnt found out how to post them on this site yet. but I could just send them directly to you it would be easier and less he said she said answers, my email [email protected]. Where is a good place to buy the impeller or complete kit from? I dont think I need the whole kit because the case is all that hard plastic. but let me know I have pics

The bottom of the reply box.There is a tab that says GO ADVANCED hit that and it opens up a new window.It will have a block about half way down that says(I think) manage attachments.That will allow you to upload pics.
I sent you a PM with my e-mail.J

The bottom of the reply box.There is a tab that says GO ADVANCED hit that and it opens up a new window.It will have a block about half way down that says(I think) manage attachments.That will allow you to upload pics.<BR>I sent you a PM with my e-mail.J