50hp force trouble

[amot69]

hello i have a problem with my engine i think i have a 1985 bayliner capri it is a 16 ft boat with a 1987 force 50hp engine i purchaced the boat from a freind this year but have been using it with him many years before i purchaced it he had a problem with the lower end slipping so we changed the forward and reverse gears it did not fix the problem we then found that the center on the prop had been sliping so we changed it with another one that we had and it cured the problem but the pitch was wrong so the boat would only rev to 3500rpms and would not plane out(michigan 072132) so this year i purchaced the original prop from iboats (michigan 072131) and now it will launch fine out of the water but around 3500 rpms it will rev really high like it is cavatating, and this is the same size prop that was originally on the boat for many years and we never had this problem and now i am plum out of ideas on what could be causing this any info would be great thank you

 

[steelespike]

Re: 50hp force trouble

Are you positive the original prop was slipping and not ventilating (cavitating in your words)<br />Are you sure the new prop is really the same?Is it possible the original was cupped?If it is exactly the same prop and not defective it should work.<br />If you removed the motor did you get it back on the boat at the same height?Did you adjust the trim for the temporary prop and not return it to<br />the original setting?Where is the antiventilation plate in relation to the bottom of the boat?<br />Have you tried trimming the motor in a little?<br /> If you are sure the original prop was spun you can have it rehubbed at a reasonable expense and give it a try.

 

[amot69]

Re: 50hp force trouble

spike i have not touched the engine in any other way other than changing the prop and the nubers are the exact same on each of the props as for antivenalation plate i honestly could not tell you its relation to the bottom of the boat i really dont even know the corect way of checking it i do know that the trim has not been touched and do not have a clue one what the setting should be it is my first boat, as for being mechanically inclined to change thing i have been a master automotive tech for 12 years thank you for taking the time to read my post and if you have any more input please let me know thanks

 

[roscoe]

Re: 50hp force trouble

The anti-ventilation plate should be approx 1 inch above the bottom of the hull.<br />See picture below.<br /><br />

<br /><br />Time to start experimenting with the trim settings.<br />Start by lowering the engine all the way down.

 

[amot69]

Re: 50hp force trouble

the cavitation plate is where you said it should be , now the trim on the other hand can you tell me what does what, what i mean is what should i be checking for when i move the pin up or down i know i am checking to see if it changes cavitation. but how do i know the proper setting and one more question is it possible that the boat could be to heavy for that 50hp engine thank you again for all of your help

 

[roscoe]

Re: 50hp force trouble

Yes, it is a little underpowered. Thats the way they sold them though.<br /><br />The lower the engine is trimmed, the better the holeshot, and less chance of ventilating.<br /><br />Raising the engine will allow the boat to get fully up on top of the water, increasing speed a little.<br /><br />The trick is to find the happy medium that allows you to get up on plane and cruise easily.