Just purchased this model 200 mercury and the lower part of motor on top of housing there is a round opening.The problem is when this whole is just above water it sprays water upward.It appears the exhaust is coming out this opening.Just wondering if there is supposed to be some type of plug for this?
This is the opening to access the allen head bolt that is one of the three that holds the lower unit on. I don't think it creates any problems not being plugged, but you can stick something in it if you want to. I put a red wire nut, upside down, in mine. It works but it looks dumb. I'm sure you can do better, it's just what I had handy at the moment. By the way, this should be under water if your motor is mounted properly (or if you have enough water in your test tank).
About electric starting, possible, yes, but there are some hurdles. The big problem is that these starters are hard to find, no longer available new. If you watch eBay carefully you will see four or five a year, and they will sell for around $60-$120. Two of these sold in the last couple weeks, for about $65 each, within a few days of each other, a coincidence. Look up Item number: 250132190358 and Item number: 250132247269 if you want to see them, a good example of each type.
Also, you need to have the toothed flywheel for the starter. And the other parts (solenoid, wiring harness, etc.). I converted my 1976 to electric start and love it, but I did spend a good bit of time and money to do it.
The starter is 50-47216 but the later replacement 50-97949 will also fit and has some advantages (permanent magnets instead of field windings, so it draws less juice) but I'd say if you find either one grab it. You can also have a non-working starter rebuilt more easily than you can find another one.
Clarification on my earlier post about the hole in the LU housing: the allen head bolt actually holds on the anode plate below it. Removing the anode plate allows access to one of the nuts that holds the LU on. Trying to find that third to remove the LU nut has driven many people crazy...