Trouble getting on Plane

[Bill Smith4]

I have a 2004 Nitro 750 dual consuel with a 115 hp Mercury. Every time I put the boat in the water after it sits for 3 or 4 weeks after starting motor and letting it warm up I have to idle about 1/2 mile to the lake where it is safe to put boat on plane. When I take off the motor will only turn about 2000 rpm and the back of boat sit down and front up adjust tilt and still will not plane. after 3 or 4 tries it will then go on plane. I trim it out and run it about 4000 to 4500 rpm's after it is on plane. Then when I stop for more than a minute or two and it will not get on plane so I repeat the process of starting motor and trying again. I had the motor tuned up after about 50 hours it helped for about 5 to 10 hours of use then started doing it again. The motor was tuned up by a mercury dealer. I only have about 100 hours on the motor.



Any suggestions as to what is causing this problem and how I can correct the problem. Thank you for any help you can provide.

 

[Bob Bourget2]

Couple things.....

Are you getting ONLY 4000-4500rpm at wot? If so, we need to look at your prop or possible motor isses. Need more accurate data. Can you tell me what prop you are running?

 

[Bill Smith4]

I am running the same ss prop that was purchased with the boat and motor it ran well at first. No the motor will run 5500+ rpm's when on plane and trimed out. Some time I will have a full fuel tank and other4s 1/4 tank of fuel. When the boat is on plane on smooth water with a full fuel tank and 2 people in boat with all gear it will run about 50 mph by gps reading and also using a radar gun I get about the same speed reading and yes the radar gun is certified to meet mfg standard for accuary and I have taught radar operation classes.



If you need additional information please advise as I would like to get this problem fixed. It would be nice to fis it during this hot weather so the boat is ready to go when the weather cool off. Thank you for your assistance in this matter.

 

[Bob Bourget2]

Your motor is designed with a "concept 2+2", which means it runs on the top two carbs below 1800+/- rpm, then will transition to all four, above that rpm. Link and synch are CRUCIAL to the correct timing of the accelerator pump, base and primary timing pick-up points. It sounds as though it is not set-up properly, especially seeing you are getting more or less peak rpm and boat speed. I would re-visit the accelerator pump set-up....

 

[Bill Smith4]

Thank you Bob B. When I get back to Lake Fork to pick up the boat I will take it to another repair shop. Any suggestions for repair shops in the Lake Fork area in Texas or in Tulsa, OK. I have printed out your response and will take it with me to the repair shop.