pitch please help

[ernie36564]

Can Some one help me as well. I have a 1989 thundercraft with 3.0l mercrusier inboard. It currently has a 19 p 3 blade prop. the boat turns only about 3700-3900 rpm wot. go around corners and it slows down. top speed about 36mph with two ppl. today we tried pulling a tube with 3 adults and 2 small kids in boat and 1 adult on tube. took forever for boat to plain out and then go around a corner it would slow down alot. with all 4 adults and two small adults boat turn about 3500-3700 rpm at wot. speed 30mph. just bought the boat and had a new head put on. the boat sat for about 2 years. any help with pitch of a prop because i don't think its good for the boat to run such low rpms and has no speed. the label on valve cover state top rpms 42-4600.

 

[ernie36564]

Re: pitch please help

it also has a alpha one outdrive.

 

[watermellonI]

Re: pitch please help

Welcome Aboard Ernie
Gonna need a little more input as to the size and type of boat, the weight of the boat itself is a factor.
First things first though, is the motor tuned and the carb and timing set?
Sometimes you start chasin a problem with speed and power thinkin its the prop when the motor s not right, make sure your motor is right first.

 

[steelespike]

Re: pitch please help

Yes, be sure the motor is properly tuned and healthy. If its turning only 3,700
w 2 aboard you would need to drop to about a 15 to get about 4,500 that seems really small to me unless you have a really heavy boat.

 

[jerryjerry05]

Re: pitch please help

Sounds like you have too small a motor for that boat.It only has 120-140 max.
The pitch on your prop should be 17c.Check the label on capacity and weight.6 people in a small boat might be overloading it. If your gonna load it with that many people you need to make sure your drive is down on take off and if you have trim tabs,use them.
Sometimes going around corners you have to lower your drive some. Jerry

 

[ernie36564]

Re: pitch please help

as far as timing, it is set and i know it has new plugs cause head was replaced with brand new one. it has points and i am not sure how to check them. i think the carb must be off some because it has a miss or surge at mid throttle when wot its smooth and idle is smooth choke is opening fully. it had 2 year old gas in it so i put new in it and today i put a 16p pitch prop on it with a plastic gas tank never used before with about 5 gal of prem. gas in it instead of using the tank on board and at half throttle still had a surge to it. with the 16p it turned about 42-4400 30-31 mph with 3 adults and small child. boat states it will hold 1400 lbs or 7 ppl. oh i checked the fuel pump bowl and it had alot of debris in it with a rock filter that was somewhat clean. filter in carb was clean as well.

 

[Silvertip]

Re: pitch please help

Checking points is a matter of looking at them for evidence of pitting and burning. You can set them with a feeler gauge (mechanically) or with a dwell meter (electronically). If you change the setting you need to retime the engine. I also feel this engine is not making full power. Since you had two year old gas in it, chances are the carb is in need of a rebuild which is why it has the mid-range stumble and probably why it is not making full power on the top end. While you said it has new spark plugs, wires, distributor cap and rotor are also parts of the ignition system that need attention as well.

 

[steelespike]

Re: pitch please help

as far as timing, it is set and i know it has new plugs cause head was replaced with brand new one. it has points and i am not sure how to check them. i think the carb must be off some because it has a miss or surge at mid throttle when wot its smooth and idle is smooth choke is opening fully. it had 2 year old gas in it so i put new in it and today i put a 16p pitch prop on it with a plastic gas tank never used before with about 5 gal of prem. gas in it instead of using the tank on board and at half throttle still had a surge to it. with the 16p it turned about 42-4400 30-31 mph with 3 adults and small child. boat states it will hold 1400 lbs or 7 ppl. oh i checked the fuel pump bowl and it had alot of debris in it with a rock filter that was somewhat clean. filter in carb was clean as well.

Premium gas is a waste of money on your engine and may actually be more difficult to burn.Don't worry about it just blend it in your tank or use it up.
As we have said give your motor a checkup something is up.You may want
to weigh your boat to see if it has absorbed water.