If you are "very mechanically inclined" then i'm pretty sure you can handle removing a nut, sliding off the old prop, sliding on the new prop then reinstalling the nut.
Lets start with a
basic primer on props. Note the following comments are general information only and there are always exceptions to the rules but for the most part this should guide you in choosing the correct prop.
Aluminum props are good all-round props that are reasonably cheap to buy and relatively easy to repair if damaged. I would recommend them if you are boating in waters that tend to have debris, rock shelves, tree stumps etc just for those reasons. SS props tend to perform better than aluminum props due to their stiffness but that performance improvement comes at a much higher initial purchase cost and if damaged, a higher repair cost. My personal opinion (& a couple of members here will disagree with me) is to avoid composite props like the plague. They are good as backups only.
As for diameter, most will be somewhere between 14" and 14.5" in this range. Usable pitch will range from 17" to 23" with probably 98% of these boats using a 19" - 21" pitch prop. The general rules are: when you reduce prop pitch your rpms increase at WOT, you get improved low end grunt but your top speed decreases. The opposites are true when you increase your prop pitch. Going too far in either direction causes performance issues and significant extra wear & tear on your engine/outdrive.
A 3 blade prop provides the lowest amount of drag & balance while in the water. It is the 'standard' when it comes to props. A 4 blade prop provides a little more "bite" which works well for wakeboarding/skiing etc & tends to run slightly smoother but due to the extra drag (more blade surface in the water) takes 1-2mph off your top end and generally runs at a slightly higher rpm than a similar sized 3 blade. There is a 5 blade (Hi-Five) prop out there that some members here use and are very happy with the performance but again at a significantly higher price. I wont try to get into prop dynamics & blade shaping/venting etc cuz it will only get confusing....
As for your tach i suspect it isn't reading correctly if it says you are running at 3000 rpm while doing 40mph with the 4.3. There should be a small dial on the back of the tachometer. If you can access it, give the dial a spin a few times then reset it to "6 cyl". Sometimes a bit of corrosion or wear causes them to misread.
All that said, your 4.3 is designed to run most efficiently between 4400 - 4800 rpms at WOT and your boat should hit the high 40's with the correct prop. Generally speaking the 14.25" x 19" pitch 3 blade aluminum prop will give you just what you are looking for. I've always liked the Quiksilver Black Diamond or the Michigan Wheel Vortex as good props for the price. Here's a link to
iboats.com and their selection of 19" props for your particular boat/motor/outdrive.
Personally i have 3 props for my 180 with the 4.3LX: a 19" 3 blade Black Diamond, a 21" 3 blade Vortex and a 20" 4 blade SS Michigan Wheel 'Apollo'. I rarely use the 21" as on my boat, it sacrifices too much low end grunt just to gain 1-2mph at top end. I probably use my 20" most of the time as for me, its an excellent compromise and has me sitting right on 4800rpm at WOT with a top GPS speed of 47-48mph. MOST people dont run their boats at WOT for long. It causes too much wear & tear and uses far too much fuel. I've found that the compromise props (19" or 20") gives that low end grunt with decent mid range acceleration & a reasonable top speed.
Best of luck & let us know what you decide to do!
confusion & questions
