Yamaha 784cc into welded mod-v hull

86tuning
Posts: 59
2
Location: BC Canada

Yamaha 784cc into welded mod-v hull

Post by 86tuning »

CedarRiverScooter wrote:
31 Aug 2019, 19:30
The latest addition to my boat is a winch mounted at the bow - the last 2 times we went out we ran up on gravel beds (obviously not paying enough attention). Fortunately we were able to lift it off, but next time I am better prepared!
Can't wait to get stuck on gravel bars. Hoping that a slick bottom coating makes life easier. But that will be after the boat gets in the water. And I'm still a long ways from that yet. Still figuring out how to put it together at this point.

Getting some arc time in with the TIG welder has been fun so far. So much more control, but I haven't figured out how to smoothy add filler rod yet. I've got both machines plugged in to separate circuits, so I can use both MIG and TIG at the same time. Both grounds connected to my table. Just farting around at this point with the machines and the process.

The Lincoln MIGPAK 180 has a ptfe liner now, and feeds smoother than ever before. With proper prep work, it's much faster, but the welds don't hold a candle to the TIG welds. Now if I could only see better with my old set of eyes, and dab filler smoother, I might just get this boat together.
the two 220v units
the two 220v units
TIG vs MIG welds, no pre-cleaning
TIG vs MIG welds, no pre-cleaning
I'm excited that I'm finally getting back at working on the boat.

See you on the water,

Brian

86tuning
Posts: 59
2
Location: BC Canada

Yamaha 784cc into welded mod-v hull

Post by 86tuning »

Well I'm slowly plodding away at the water inlet. In the meantime, I did find the service manual for the waverunner here:

https://www.manualslib.com/manual/10588 ... e=1#manual

And it's been quite useful so far. I'm trying to put the engine as far back as I can, to increase cockpit space in the boat. The plan is to shorten the driveshaft and the intermediate shaft. And intermediate shaft shortening requires disassembly. The service manual is helpful for that. Short story is that the shaft is pressed into the bearing, and the coupler is threaded in place, and retained with pipe sealant.

Also found the parts catalog for the waverunner here:

https://www.yamahapartshouse.com/oempar ... 800z-parts

Apparently the 1100 waverunners use a shorter intermediate shaft. Make sense, as the triple cylinder engine is longer. But the couplers are the same, so I could use the 3-cyl shaft to move the engine back, and not have to shorten my 2-cyl shaft. If I can find a used one. But I may be able to shorten the 2-cyl shaft even further to move the engine further back by an inch or two. But that's a tomorrow problem.

Cheers.

-Brian

CedarRiverScooter
Posts: 973
5

Yamaha 784cc into welded mod-v hull

Post by CedarRiverScooter »

Sounds like you are enjoying the analytical phase of the project.
Maximizing cockpit room is a worthy goal.
Keep the pictures coming!

turbotodd
Posts: 1179
8
Location: 72032

Yamaha 784cc into welded mod-v hull

Post by turbotodd »

A couple musings of that engine (XA800).

They are kind of peaky even with the power valve system. In other words, kinda hard to vary the power, beginning at about 1/4 throttle. From there, you are at maybe 25% power, but at half throttle you may be at 75% power, kind of like an old 2 stroke dirt bike. I always liked them but they weren't real smooth in power delivery in the factory installed application.

Secondly-if you decide to test run out of the water, you get about 10 seconds. Once the spark plugs begin to glow (and they will), it will literally diesel, you can't shut it down. The first time this happened to me on a ski what was started without water in it, I about pooped my pants...brand new unit, couldn't get it shut down, was sitting there running. I pushed the stop button. Then removed the lanyard. Then both plug wires pulled off,still running about 6000 RPM. I had no idea what to do. After maybe a minute, during the time I was trying to get to the air intake to starve it, I reached over and pulled the choke knob out, which then killed the motor. No telling how hot it got. To my knowledge it never did show back up for any engine troubles so maybe it was ok. I mentioned the issue to our then yamaha rep, he said that the 800's and 1200's were susceptible to this from time to time. They also said that the 800's especially were really "peaky" in their design and that some folks would probably complain about it-and they did. But they were fast.

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