18.5' Starcraft Starchief with 140hp Mercruiser prop question

[tcooke]

So my boat is a 18.5' Stracraft Starchief, I dropped in a rebuilt 1978 Mercruiser 140hp with a pre-alpha 1.98 leg on it. My question is I am currently running a Rubex 14.5" 19p prop and my WOT is 3600 rpm, pushing at about 33-35mph, hasn't changed no matter what. I have rebuilt the carb, replaced the exhaust shutter and checked the fuel pump. I was looking for some info from other starcraft guys out there to see what they are runnig in thier boats. Or would be willing to hear some suggestions on props in order to get my rpm back up. Is it as simple as dropping down to a 15p? What about the diameter size? Also would dropping to a 15p lower my speed and raise my rpm or would the speed stay the same while increasing the rpm.

Thanks

 

[steelespike]

Re: 18.5' Starcraft Starchief with 140hp Mercruiser prop question

Your about 1000 rpm low. Usually it takes about 5" of pitch to make that up.
Seems extreme to me.
You might check the antivent plate is about even with the bottom of the boat maybe that pre alfa leg requires a different height. Isn't likely to cause 1000 rpm drag but may contribute to it.
The boat should run about 40 at 4600 to 4800 rpm.
You might varify the tach is accurate; roughly speaking it seems about right in relation to your speed.Be sure the throttle opens all the way,that the timing is set right and advancing as it should,all plug wires hooked up and firing.Don't assume all is right just because it is a recent install.
There is a Starcraft forum right here at iboats.