I/O

Question
I recently purchased a boat in a box. The motor is a 4.3 v-6 that was just rebuilt and sitting on a stand. The out drive is an older alpha one (87 thru 90 according to the sn) The boat is a 91 wellcraft 17 sport bowrider that orig had a 4 cyl.
OK, I had all accessories rebuilt (starter, alt,4 bl roch carb,) I took it out for the first time today and I could only get 3500 rpm at 35 mph with a 19pitch prop. switched to 17 and still only get 3500 rpm at 30 mph. What do you think the reason I can only turn 3500 rpm is? also I forgot to put in a water temp sender, the man. talks about one and I found the tan wire they talk about but I cant seem to find out where one goes on the engine.  

Answer
First of all what is the gear ratio of the outdrive? Second after you figure whether the gear ratio is correct for your new engine, the next step is make sure the engine goes to the correct rpm out of gear, with out blowing the engine.Next the diameter of the prop can be adjusted for rpm. I would call a prop shop and ask them what is the correct prop for your boat. After you do the following you will either be doing the correct rpm or check back.

                bruce