85 Mercruiser I/O will barely move past idle speed at full throttle

OK so I have an 85 17' Chris Craft with a 85 (I believe) MerCruiser I/O 140 (serial 06920736) with alpha 1 outdrive.. here's the issue bought the boat 2 years ago took it out on the water it would run and idle great come up to plane fine and the speedometer would say 50-55mph top speed, but while going between idle to full throttle sometimes it would stall out and take a few times to fire back up (thought it was just the carb needed to be cleaned but didn't get around to it)... ok that was the beginning delt with it a few more trips everything was ok... Now present day the boat sat for lets say a year and a half (winterized of course) so did massive cleaning job bought new battery, then installed new spark plugs,new wires, new points, new starter, new fuel filter, rebuilt the carb to specs cleaned it well with gallon can carb cleaner (soaked all parts) and blew out with compressed air. started it in the driveway with muffs fired up after a 2 pumps on the throttle idled very well in the driveway when it felt like it sometimes the motor would shake the boat violently but would calm down, adjusted the idle screw then it ran fine at idle 500-600 rpms. took the boat out today took a few tries but started up and idled good in the water, then stalled when tried to put in gear... finally got it to run in gear after playing with the throttle a bit and adjusting the idle screw... so now I am idling through the no wake zone and its fine burning a little lean and sometimes violently shaking the boat but going.... now out of the no wake zone go to give throttle it stalls and backfires... play with the throttle and I can start to gain speed but it will not go above 2000 rpm even at full throttle and the boat will not gain any speed maybe a few mph over idle speed. the prop is a little dinged up but the same way it was when it would plane fine and get up to speed fine.

so after that novel my issue is that on the water with the prop spinning the boat will not gain any speed maybe a few mph over idle and not go above 2000 RPMs....

any ideas hopefully I can fix this and get back on the water next weekend....

Re: 85 Mercruiser I/O will barely move past idle speed at full throttle

Sounds like you have a couple of issues....

Regarding not being able to get to speed - From the description, it sounds like your prop hub has slipped. Try a spare prop and see if it makes a difference. If you don't have a spare prop (and you should) - then make a mark of some kind on the outside of the prop and the inner hub - see if they are still aligned after running the boat.

On the rough running issue. Did you get rid of the old gas?

Re: 85 Mercruiser I/O will barely move past idle speed at full throttle

Good point about the hub come to think of it the last time I had it out I tried to drive it up on the trailer...( I'm a jet ski and wave runner guy) and went right over the side of the trailer and believe the prop may have hit....

As for the gas I did take out Most of it then refilled with premium that may just need to burn the rest of the old I guess?

Also could this be a timing issue as well ( a friend suggested) I am going to get that done this week

Re: 85 Mercruiser I/O will barely move past idle speed at full throttle

I did not take the boat out yet but I did put it in gear (without the boat running of course) and try to turn the prop by hand and it would not budge. could this be another way to prove the prop is ok or is that not enough load compared to being in the water?

Re: 85 Mercruiser I/O will barely move past idle speed at full throttle

Trying to do that by hand really isn`t enough force to make the prop slip even if it is bad. Might but I don`t think so. (been there!)

Re: 85 Mercruiser I/O will barely move past idle speed at full throttle

ok makes sense I will just have to bring the other prop with me when I go on the water after I fix the other issue I found (started a new thread for) and see how things go. Thanks