messing about in boats

Last fall, Ian and Mark and I bought a boat from a co-worker of mine. The way he talked about the motor -- a little old, but barely used; it just hung on the wall -- made me think we were getting a good deal on a great boat. The guy is a real dealer -- he said once he doesn't own anything he wouldn't sell for the right price -- and while I don't feel cheated at all, I did admire his salesmanship. Maybe the motor was barely used. I just know when I first saw it, it was older than I'd imagined, and there were a lot of leaves under the cowling, and grease, and pieces broken off the cast aluminum frame. 
My co-worker motored down from the other shore and took us for a ride. He opened the throttle and leaned the gunnel deep into a turn. It made us children again, so we bought the boat, for $233 each.
We took it out exactly twice last fall. On the first outing, I broke the tiller. For a while, we weren't sure how it happened. Then I remembered my co-worker's warning about catching the tiller on the stern seat when you tip the propeller into the water, words that must have meant little to me before I knew how to clamp the motor to the transom. By pushing the tiller to one side (to engage the throttle rods) and steering with the other hand, Ian and I were able to joyride, but it was bittersweet. A welder tried to reattach the broken ring, but the aluminum had too much molybdenum to weld, so we braced it with a thick washer, some tiny screws, and epoxy. On the second trip, the gas we thought we had in the tank turned out to be mostly ice and water, although it took us a while to figure that out, too. Luckily, we had motored upstream. We paddled back. We debated whether or not a floating boat moves the same speed as the current.
A note about our boat: She's 12 feet long, three feet at the beam, and flat-bottomed. The freeboard is maybe 17 inches, and the rated capacity is about 500 pounds (although we hope to hunt moose with her). The boat is designed for a motor up to 7 hp.
Our motor is a 1969, 25-horse Evinrude, which apparently was the go-to motor on the Yukon in its day. Although it's known for its power-to-weight ratio, the motor weighs nearly as much as our boat. To support it, we beefed up the transom with steel plate and all-weather plywood.
The boat was made by Monark, so we named her the Ark.
We took her out again last night. Ian and I tried to go Sunday, but spent a few hours yanking the pull cord, futzing with the choke and fuel mix, and watching her sputter to life and die out over and over again. An old guy from the Lower 48 tried to help, and while we figured out later he didn't know a damn thing -- what he thought was a priming pump was actually the kill switch -- his poking around helped us learn a few things, like how the cam works the throttle. We had to move when some guys wanted to shoot golf balls off the deck of the bar whose dock we were using.
That night, I read about old Evinrudes in online chat forums. On Monday, I went to the boat shop and got some advice and carb cleaner, and after work, Mark and Ian and I took apart the motor -- part of it, anyway. We checked the fuel pump for leaks and a fuel line for cracks. We disconnected the fuel mix linkage, choke, throttle, and fuel line, removed the carburetor, and unscrewed the bowl from the lid. Our experience with carburetors was mixed. Ian had once been shown how to disassemble and clean the carburetor of a VW bug. I've always been too scared of the delicate pins and calibrated floats to open my motorcycle carburetor. Mark had cleaned the carb on a lawnmower once -- he spit in it and wiped it with his t-shirt.
The second we opened the carburetor, our problem was clear. Waxy gum filled a whole section of the bowl and lid. It was the most likely problem -- the Occam's razor of boat motors -- and with hindsight, completely predictable given how we'd left the motor over winter. I think it was a combination of frustration and forgetting that led us, after trying to run the motor on ice water, to put it away without running fuel stabilizer through it or even running it dry to get the water out of the shaft. (Nor did we grease the drive parts, before or after winter.) 
We scrubbed the carburetor with Ian's toothbrush, cleaned the choke lever, and wiped out some leaves and grease, then tested her with the prop in a tote of water. She ran! We experimented with fuel mix (the numbers on the knob don't make any sense), then shifted into gear and churned water into froth with the prop. When we shut it off, Mark realized there wasn't any cooling water getting to the motor -- we didn't have the prop deep enough. There was smoke coming out a hole in the shaft. We figured it was fine. I thought about filing smooth the dents in the prop, but didn't.
Last night, Ian and I slid the Ark into the Chena. The motor started on the third pull, rough at first, then smoother. We powered upstream, carving turns in the water, high-fiving, squinting into the sun. We slowed to tame our wake for floaters. I scanned the water for hints of shallow ground and hugged the outside around bends. And then we hit. The prop must have been pushed to the side, because the boat curved sharply, once and back, and for a second I thought we were going in. The prop ground against the bottom. I knew from canoeing it was shallow there, but had forgotten, or let it go when I couldn't see signs on the surface. (We saw them later.) Something sounded bad, so we cut the motor and went to shore. We couldn't figure out how to get the prop off, so we pulled the boat to deeper water and tried again. It sounded okay. We hit bottom a few more times. The prop was chipped and chewed, but still moved us along. It occurs to me now that learning to read the river will be harder than learning to fix the motor. As it should be.
We probably draw a foot of water on step. At low speed, the boat stays flat. Add some gas and it tilts up, plowing through the water and pushing the prop a few inches lower. Add more gas and it starts to plane again. We met up with Mark, and he hit bottom. He pegged the throttle. We debated whether or not the Ark could tow a waterskier.
On the way back downstream, Ian wanted to try the extreme setting for the angle of the prop, a few degrees off where we had it. I said I couldn't remember, but thought it might have been where it was for a reason. I drove. The boat seemed less willing to plane, and the steering seemed slower. Ian tried it. At full throttle, the boat began to level out. It rocked, and then the bow started to jump and crash on imaginary swells. We couldn't steer, and for a second I thought we might crash into a much-nicer boat docked on shore. Ian cut the gas and steered away. We switched back to the old setting. He didn't have sunglasses, so I drove. When trees blocked the sun, goosebumps covered my arms. I went fast. The boat steered effortlessly, and the motor ran smooth.