prop change, speed stays the same?

[guido469]

Ive got a 1652 MV lund with a 1985 merc 50horse. I went from a 11 1/4 10p prop to a 10 3/8 13p prop and speed never changed. I used to have a 1977 evin 25horse with a 9 1/4 11p prop and it ran the same speed as my 50 i now have-30mph. Does that make any sense?

 

[steelespike]

Re: prop change, speed stays the same?

To make any kind of judgement we need your max rpm at max speed,a discription of the overall performance would help as well.
A tinytach is about $40 and easy to install.You might tell us about your 1652.
Sounds like a Jon.Were props both al. same brand?Did it make 30 with the 10?
and again we need the rpm.My first guess is something is up with the 50,possibly being further comprimised by a poor setup.

 

[guido469]

Re: prop change, speed stays the same?

Not having a tach is hurting me. There both michigan props, alum.Boat is a mod v and loaded weighs about 1200lbs. The prop shop told me that it call for a 14pitch, so i bought a 13 for when i run more weight. It ran 30mph with the 10 and does with the 13 too. Motor runs very well, boat jumps out of the water in a hurry and has no problems keeping the rpms. The marina i bought the motor set it up for me so i assume that its right( i know you shouldnt assume anything but...)

 

[steelespike]

Re: prop change, speed stays the same?

Does it feel like the same speed?Speedometers can be inaccurate.
The antivent plate just above the prop should be about even with the bottom of the boat.Check that the throttle plates are opening all the way.Observe their action with the motor off and in forward.Be sure its running on all cylinders.
The manual has about 2 pages of instructions and illustrations covering the ignition.
and carb sync.Did you play with the trim?