My 1969 Sea Doo 372

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One fancy and expensive paint job!

The 1969 372 Sea Doo adventures began unexpectedly.....
It had been years since I'd given a thought to our old Sea Doos, and even longer since I'd ridden them.
Then early one Sunday morning in the Spring of 2004 my brother Tori and I stumbled across two 1977 Dynafoils at the local Swap Meet.  Dynafoils are quite possibly the rarest vintage watercraft in the world with only about 530 ever built.  But that's a whole other story that you can enjoy on my sister website:
Fast forward to a couple of months later and Tori had purchased the two Dynafoils along with their trailer and a third one as well.   I took one, rebuilt it and started riding it.  Or as we say in the hydrofoil world..."flying" it. 
Once the Dynafoil was completed I started reminiscing about the good ol' days and our 1969 Sea Doos.  I posted a few ads on the internet and one day got an email from a seller who turned out to be about 4 hours away in Sacramento, California.
A deal was struck after I received the above photo of the Sea Doo sitting in his shop, and I picked it up on November 5, 2004.
That Wild Paint Job:
You're probably thinking; 'what's with the paint job?'   Well, I was thinking the same thing until I saw it in person.  That is a very custom paint job done by the previous owner who has a high-end bodyshop in the east bay are of San Fransisco.  All of the graphics are hand done and there is a mile of hand drawn pin striping.  He even put his son and daughter's names up in the cowling in front of the handle bars.  The blue and pink are candied metallic and the whole thing is done in a clear coat, so it's all smooth as silk.  Pretty amazing!
The Rebuilding Begins:
The Sea Doo's hull was in very nice condition, and needed nothing.  However, the engine was another story.  It was rusted solid and after numerous attempts, I finally broke the pistons out of it.  During this final bit of butchery, I broke a connecting rod on the much for that engine! 
On to the jet pump.  The first thing that sold me on this Sea Doo, other than it being here in California, and the nice hull, was the super nice jet pump.  It spun and looked brand new.  When I located the previous owner, he told me that he'd had the pump completely rebuilt by a form Berkeley Jet Drive employee who owned a jet pump shop in the San Fransisco Bay Area.  That was certainly a nice surprise.
The Parts Search:
Once again, the internet and eBay to the rescue.  I stumbled across a seller who had a "Berkeley Jet Pump from a 60's vintage boat" for sale.  I immediately recognized it as the unique 6JA pump used on the 1969 372 Sea Doos.  I emailed and asked if he still had the engine that powered the pump.  Sure enough, not only did he have the engine, but he also had the muffler and a few front and rear storage compartment doors.  I wound up buying everything from him!
His engine had a bad crank and a cracked lower crankcase half.  So I sent the crank away to be rebuilt and used the good crankcase halves from my own boat's engine. 
In the meantime, I found a lady who's Dad used to have a ski-doo dealership and had a numbe of Sea Doos, plus parts.  I bought quite a few engine parts from her and her sister sold me copies of an original parts manual, the owner's manual, a couple of dealer brochures, and a video with about 15min of original Sea Doo demonstration riding footage.
The First Ride:
By January 2005 I had the engine finished and running, and the Sea Doo went on it's maiden voyage.  Unfortunately, this ended in a tow back to the marina behind the Dynafoil.
It turns out that the previous owner (the one who'd given it the fancy paint job and restored it mechanically) had put the engine coolant hoses on backwards.  I didn't have any photos of how they were attached originally, so I just put them back the way he had them.  The correct orientation of the coolant hoses coming off the jet pump housing is to have the right side one feeding the watercooled exhaust pipe.  The left side one goes to the side of the cylinder block, just above the starter flywheel.  (I'd put this one going up to the top of the head)  The engine outlet hose comes off the top of the cylinder head and goes out the back of the boat.
So, with the hoses backward the engine overheated and shut down.  It wouldn't restart and that's probably a good thing.  Fortunately, I use Torco Synthetic 2 stroke oil, so no damage was done.  By the time we got it towed in, it would fire right up.
Exhaust System Problems:
My next trip to the lake was mostly a success.  But after about 45min of non-stop full throttle fun, the exhaust started getting louder.  I popped the seat up and found the rubber coupler between the exhaust pipe and the muffler was burned through.
During my rebuild I'd had a new exhaust pipe made out of 2 mandrel bent pieces of exhaust tubing.  The shop was able to install a water cooling tube too, and it looked just like the original when completed.
But, there was one thing we didn't do.  The old exhaust pipe had been rechromed.  In this process, the water cooling tube had lost it's little "flute" holes near the tip that are positioned 90 degrees to the pipe so they spray water against the pipe and the rubber coupler.  Having not known about them, my recreated exhaust pipe was also missing them.
It wasn't until I bought a 2 original Sea Doos in March 2005, that I discovered the "flute" holes in the original exhaust pipe.  After drilling the same "flute" holes in my own exhaust pipe, the problem was finally solved!
Difficult Hot Starting:
I still haven't resolved this issue, but I'll mention it and update here when I do.  Originally, when I first finished the engine, it would start cold, with just a blip of the electric starter.   However, after running for a while, if shut down, it wouldn't restart.  If it did, it was very difficult, and usually it would only restart with the pull starter. 
I've rebuilt the carb with no change.  I've put on an even nice carb, that's been change.  I've tried different spark plug gaps and new change.  Played around with the change.

However, it starts better with the pull starter and generally won't start at all with the electric starter.  I find this very interesting, because the magnetos make voltage for the ignition coils when the engine is turned over.  The coils aren't powered by the battery as they are in an automotive (4 stroke) engine.  Could it be that the ignition coils are marginal, and they need that extra boost of more cranking speed that you get from the pull starter, in order to generate a spark under the load of compression?  Mmm.....
Jet Pump Improvements:
One thing I've been working on are improvements to the jet pump.  First thing I did was to open up the very restrictive intake grate.   I used a hack saw and cut out 2 of the fins.  This left a fin in the middle and a fin on each side at the very edges of the grate.  Then I took my die-grinder with an aluminum grinding bit and I shaped the fins so they were very clean and air foil shaped, like a propeller blade.  I also put a 3/8" radius along the "back" curvature of the intake grate where there was just a sharp wedge type of angle. 
All these mods promote more water getting to the pump and it makes a difference in the performance.
The other modification was to work with an impeller shop in Los Angeles and have a modern stainless steel Skatrax impeller modified to fit.  They detuned the pitch to suit the low horsepower of the engine and it has really improved the planing speed and doesn't seem to have effected the top speed much, if at all.
More on this as it developes because I want to do some actual speed comparisons between the original and the modified impellers, along with some rpm comparisons.  I may choose to detune the impeller a bit more to see if I can bring up the top speed a bit.

"Come on Dad.  Let's go!"
My daughter Kate Jan. 31, 2005