Prop? Motor height? Or both?

[komatsu200]

I just purchased a 1988 Blazer Drifter X-17 (17') boat with a 1982 90hp Evinrude. The plate on the motor says (operating range 4500 to 5500 rpm). Using the power tilt and trim I can get the boat to plane out nicely but no matter what I try I can't get over 3000 rpm. The prop that is on it is a (13-1/4 x 17) and is in pretty rough shape so I'm planning to replace it. After reading a few of the post on here I think the motor height may be a little high too. I've taken a straight edge and placed it along the bottom of the boat and measured from it to what I think is the ventilation plate. The plate is 3" above the straight edge. Would lowering the motor help me get above 3000 rpm? Would I need to go with a different pitch prop? Or should I try a combination of both? And if so which should I try first?

 

[V153]

Re: Prop? Motor height? Or both?

With the amount of backset you have the height is probly okay. What speed(s) are you obtaining?

If the tach is accurate it sounds to me like you're not getting wide open throttle. Remove the motor cover and air box cover then shove the control to full throttle. Are the carbs opening all the way?

 

[komatsu200]

Re: Prop? Motor height? Or both?

I'm not sure what speeds I'm getting because the speedometer doesn't work right now. I just took the covers off and checked the carbs and they seem to be opening all the way.

 

[steelespike]

Re: Prop? Motor height? Or both?

Most boats are barely on plane 18-20 mph at 2500 to3,000 rpm So if your up and running at speeds around 25-30 or more your over 3000.
Unfortunately without rpm"and" Speed you can't really evaluate your setup.

 

[komatsu200]

Re: Prop? Motor height? Or both?

Thanks for your replies. It looks like my step is to get my speedometer fixed. Is there anyway that I can test the tack to see if it's accurate?

 

[steelespike]

Re: Prop? Motor height? Or both?

You could compare it to another tach.Perhaps borrow a shop tach or use one of the aftermarket tachs like the tinytach.As far as speed perhaps a friend with a gps could help you out.As far as the speedo check the pickup and the tube for damage and or water intrusion.The gps would be much more accurate.