Motor and boat question. Mercury 650cc 1970 4 cyl 65hp

[y2jericho]

On my little boat i have this phat phart motor on the back. My boat is a 4.33 meter de havilland f/glass<br /><br />The motor relatively workds fine with 95-100lbs of compression accross all cylinders on cold reading<br /><br />I have a couple of questions though ... My mechanic replaced the gearbox with a 115hp motor's of the same era and he said the ratio would be different so he compensated with another old prop. The old prop is a bronze one and i can't tell what pitch it is it is not written on it.. So i put the boat in the water... warmed her up realising now i can lift the warm idle to 3500rpm instead of the previous 2500 rpm (changed control box) and i put throttle WOT... After 2-3 seconds i was flying but i realised it was at the end of my tacho (7000rpm) so i slowed her down and kept her at no more than 5300 for the whole journey....<br /><br />Could it be that the propellars hub is fawked or do you think it could it be that it is not the correct propellar... For a boat of this size and a motor as such and the gearbox what propellar do you think would be best suited ot reach the 5500 rpm (which i won't be using much as i will try to keep her at a rpm of 4800 or so only want extra bit just incase i take family memebrs on board...<br /><br />With this bronze prop i currently have giving me these way to high rpm's.. If it turns out the hubs alrite do you think this would be a good skiiing prop as the skis would lug the boat down and i could probably reach 3/4 throttle and about 5000 rpm with it with a skier but the lift is tremendous.. .the boat was on plane in 2 seconds<br /><br />.. also just another question.. When running the motor with the muffs should the water coming out of the peehole be warmish and not cold? same as on the water? Its not like warm water but its definately warmer that cold <br /><br />Thanks a bunch guys in advance and hello from Australia where it is in Season all year our winter is basically your spring

 

[RICKRICK1]

Re: Motor and boat question. Mercury 650cc 1970 4 cyl 65hp

y2j-- I would talk to your mechanic and get back your old prop if you can. If not I would start at a 15 or 17 pitch 3 blade prop and see what happens, and you can go from there. I dont think the pro shaft you are using is bad, If it was you would have rpm but no speed in most cases and you do say it is "flying" your boat.<br />hope this helps. Those two blade props really turn some rpm as there is less blade area to push against the water.

 

[y2jericho]

Re: Motor and boat question. Mercury 650cc 1970 4 cyl 65hp

its a 3 blade prop that is the thing <br /><br />I can't get the old propellar off because the thing is fused onto the old LU because the rust and corrossion is killer.. The old prop was bent and wasn't a perfect circle so i would be wary putting it back on