Re: 4500 rpms is all shes do
 

allmost forgot, and this should be the first thing you do before you do any other trouble shooting, is the tach accurate? Check it with a known good tach or a shop tach

Re: 4500 rpms is all shes do
 

labii's got the same CC and motor...hope he'll show up here and tell us what prop he's got ;) ...

Re: 4500 rpms is all shes do
 

thank you for all your effort for me spareparts and everyone else who had ideas , hope i can help someone also pay forward. will let all know the results and what will solve it. thanks again

Re: 4500 rpms is all shes do
 

If the motor is tuned and all else fails try down sizing from the 15 inch prop, it may be too much . Try a 14 1/4 x 17 prop and see if your rpms come up. That should get you over 5000. One other thing may be the motor is too low in the water. Make sure your cavitation plate is even with the keel of you hull before you switch props.
Dennis

Re: 4500 rpms is all shes do
 

A friend of mine had a similiar RPM problem. Finally found out that the fuel line was collapsing. Therefore, restricting the fuel flow. Replaced the fuel line with the correct size,problem solved.

Re: 4500 rpms is all shes do
 

thanks again for all suggestions, bit the bullet and took it to the yamaha service man.....rebuilt all carbs. now 5400rpms and 43 mph. yamaha serviceman said worse he's seen in a while....using a 151/2 x 15 s.s. prop