Vintage Boat Cross: Bikes in a Boat

Two friends, a Honda SL90, a Honda CT90, a Chrysler Sport Fury, and a trail on the other side of a lake. Enter the boat pickup!

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by Seth DeDoes
And it was this last asset, the generous floor area, that hooked me, because the Sport Fury’s cockpit, measuring over 6 feet long and 5 feet wide, looked similar to a pickup bed in size, which, as every hillbilly knows, is just right for carrying dirt bikes.

There it was. Just another old Craigslist motorboat. Faded and forlorn, a 1970 Chrysler Sport Fury lazing in an equally fusty dirt lot, its formerly gleaming Pirates Gold, 16-foot hull chalky and dull, its interior moldy, and its 85 horsepower Magnaforce outboard engine entangled in creeping vines. Once a catalyst for family fun, it was now neglected and needy, like a dusty, swaybacked nag. Its time, quite sadly, had passed. Or had it?

I’m a hard-ass in some ways; a vigorous competitor in the waves, on the track and in defending moral principle. But I’m a total softy when it comes to those suffering undeserved misfortune … and also neglected machinery. I fell in love. I opened my wallet. I bought it.

Superficially, I had merely fallen for a needy boat. But I soon became infatuated that the boat, engine and trailer were all produced by mighty Chrysler Corp. during its 1965-1984 dalliance with America’s recreational boom. What other car company had the stones to do that? Most importantly, though, I liked its shape. Hardly beautiful by marine design standards, Chrysler’s “Cathedral Hull” runabouts debuted for 1969 promising superb stability, affable ride and handling, great value and roomy interiors. And it was this last asset, the generous floor area, that hooked me, because the Sport Fury’s cockpit, measuring over 6 feet long and 5 feet wide, looked similar to a pickup bed in size, which, as every hillbilly knows, is just right for carrying dirt bikes.

“Huh,” I thought. “Dirt bikes in a boat …”

A spacey odyssey

If an asteroid can hurtle through space for 4.6 billion years before igniting in the Earth’s atmosphere, why can’t an idea do the same in our cosmic brainpans? Ten years ago, I had stood on the northern shore of a pretty lake while traveling through California’s Sierra Nevada. No paved roads encircled the lake, but there on the other side, amidst a backdrop of craggy hills, faintly appeared some trails. And the sight excited my prefrontal cortex with a desire … go ride them. But how? The discovery of the Chrysler boat online, and remembering a 1969 Honda SL90 long moldering in my own garage, made the answer abundantly clear. Yet while this sketchy boat/bike concept practically designed itself, making it real would take some work.

Mad for Motosports

What is it with unfulfilled dreams? Since high school, one of mine had been to own a Honda Motosport 90, aka SL90. Whereas the related CL90 scrambler and S90 street bike had dopey stamped-steel “T-bone” frames, the Motosport 90 uniquely featured a dual downtube frame, internal-spring fork, high-mounted fenders, fatter universal tires, and proper dirt-bike styling.

Naturally, after slumbering for decades, the Honda wouldn’t run. A sulfated battery, a carburetor full of dodgy-looking chemical nodules, dark gooey oil in the crankcase, jammed control cables and an inoperable speedometer all surfaced as I began Operation Motosport CPR. A new battery (hooray, only $20!) made spark happen, but deeper problems lurked within the tiny Keihin carburetor. Here, every passageway that could be clogged with old gas residue or aluminum oxide was. Also, the slide was frozen in its bore. Lacking a volcano to chuck this tired little Mixmaster into, I set to work. A long soak in carb cleaner followed by dental hygienist-caliber handwork with a pick (originally purchased for dissecting rats in grad school) and other medieval tools got it done.

Swapping rubber seals between the SL90 petcock and a spare CL90 unit produced a working fuel system, excepting one critical component: sunken gasoline-filled floats. Unable to do their job, namely float, they let the engine flood continuously, leading to hard starting and an awful overall state of tune. A magnifying loupe revealed badly pitted brass – a no-fix situation. Repetitive searches produced exactly one OE SL90 float in the U.S., and it was 2,500 miles away and cost a heavy $85. With a trip looming, I bought it, and the SL90 was reborn.

But my travel buddy, JG, also needed a bike to ride, having sold his vintage Suzuki DR350 a few years back. Luckily, friend Mark came to the rescue by offering his freshly restored 1970 Honda CT90, with the provision that it return undamaged. We were bike-ready.

Rehabbing Rube Goldberg

Until removing the Chrysler’s engine cover, I thought I knew 2-stroke engines. They’re simple, actually. In their most basic form there are just three moving parts: crankshaft, connecting rod and piston. But under the Chrysler cowling was a rat’s nest of wiring, hoses, rods, bell cranks and belts. Worse still, this mechanical maze wouldn’t run when I hooked up a fuel tank and car battery, and turned the key.

Unlike a classic bike, which uses gravity to fill the carburetor bowl(s) with fuel, the Chrysler outboard has a vacuum-operated pump to deliver premix from a 6-gallon tank to three Tillotson side-draft carbs. Primitively, the starting process requires squeezing a rubber priming bulb to lift fuel from the low-lying tank to the fuel pump, which wasn’t working due to an air leak at the quick-disconnect coupler. No fuel meant no engine start. Rats.

Fortunately, a new coupler was easily sourced, and after removing the float bowls and cleaning the carb passageways, the bowls filled nicely. But the engine still refused to start, instead backfiring dramatically out the exhaust system, which was immersed in a washtub and plastering my house with premix-tinted water in the process. No bueno!

Fearing a sheared flywheel key, I checked the ignition timing, which was way off. Fortunately, adjusting the timing required only fine-tuning a threaded rod attached to the distributor. After more trials, I learned the engine likes lots of throttle to start, and with that bit of intel it caught and idled fine in its little private hot tub. Things were looking good.

The load in

Finally, after weeks of fussing, it was packing day. Into a new 2018 Ford F-150 turbo-diesel’s bed went the two Hondas, and into the boat went two 6-gallon marine fuel tanks, an aluminum loading ramp, a surfboard, a fluke anchor and chain, two paddles, and dock and bow lines. Our riding gear, life jackets, clothes and a cooler went inside the F-150, which did a fine job hauling and towing our vintage flotsam-and-jetsam collection.

Hitting the highway to escape Los Angeles, I was relieved to find the boat and trailer towed beautifully. Worried about the two-lane roads stretching like a lazy blacksnake across the hot Mojave Desert, before leaving I’d replaced the trailer wheel bearings ($30), added new Bearing Buddy protectors and marine grease ($40), and had new Carlisle 6-ply tires fitted to the diminutive 12-inch trailer rims ($180). Never was money better spent, because the trailer behaved perfectly over nearly 1,300 miles.

On a Friday morning in late summer, the lake was about as deserted as deserted gets. A few old-timers were fishing, but elsewise, all was quiet, with no Jet Skiers, wakeboarders or pontoon partygoers extant. Except us odd ducks. Make that edgy odd ducks, because the time had come to test the hypothesis that an old rattrap speedboat could be repurposed as an aqueous pickup. Plus, feeling responsible for my friends’ safety gnawed away at my gut.

Hull and inspiration

Weeks prior, I had reverse-engineered the bike-loading process, starting with how the bikes should be unloaded once we reached the far side of the lake (assuming we got that far!). This approach required rolling the bikes into the boat backwards, and that’s exactly what we did.

Right there in the dirt parking area above the launch ramp, I lowered the truck’s tailgate, positioned the ramp from the pickup bed onto the boat’s wide bow, cinching it to the bow cleat with a tie-down strap. After untying the SL90, JG and I lifted the rear wheel onto the ramp and rolled it up and backwards toward the boat. When the rear tire was about to drop over the bow we climbed into the boat’s forward seating area, and each grabbed one handgrip and the saddle. From here, we were able to first lower the 220-pound Honda’s tail end, and then its front end, slowly into the boat.

With its footpegs folded, the Motosport 90 rolled aft through the walk-through windshield area until the taillight met the splash tray near the engine. While not harmful at rest, much jostling in this position would certainly break the lens. Luckily, a two-by-four under the rear tire lifted the taillight just enough. Using the boat’s aft cleats, we secured the SL90 at its upper shock mounts, then added a third tie-down from the fork forward to one of the boat’s windshield mounting post. The SL90 was solid.

Encouraged, we repeated the operation with the Trail 90. Lighter at 205 pounds, it proved easier to roll up the ramp, but the narrow walkway near the Chrysler’s bow proved a tight storage fit. Yet by folding and protecting the rubber footpegs with shop towels, and employing three more tie-down straps, the bike was snug as a bug in a rug. We were extremely lucky with the fit; 250s, 175s and maybe even 125s likely wouldn’t have worked. Better lucky than good!

Sink or swim

Backing the Chrysler and its two-bike cargo into the lake with the F-150 and its rear-facing camera was ridiculously easy, and we’d strategized to position one guy in the boat and another on the dock holding bow and stern lines. As soon as the Sport Fury floated free, truck and trailer scooted back up the ramp. Simple.

With all aboard and all systems apparently “go,” I asked JG and photographer Seth DeDoes if they could swim. I don’t think they enjoyed the trolling much; they were as worried as I was. There was nothing left to do but turn the Chrysler’s ignition key, push it in to activate the electric chokes (a weird boat thing), and then turn it to start. Despite sucking wind at 8,000 feet, the wizened old engine started instantly, snorting, shaking and smoking like Churchill on a whisky bender.

Shake and wake

If you’ve ever ridden a Kawasaki Mach III in anger, please raise your right hand. That is, if you still can. Because at WFO, that 3-cylinder, 2-stroke buzz bomb on wheels vibrates like a paint shaker full of claw hammers. And it’s only 500cc in size. Meanwhile, the Chrysler triple displaces 1,186cc – more than twice the Mach III with the same cylinder count. As such, I will freely admit that when advancing the throttle for the first time, I was as nervous as when lining up for a race. Would the engine stumble and die, or shake itself off the transom? Or would the strangely loaded hull nose underwater, or worse, roll over and sink? This was a gamble – and we all knew it.

But, winner! Instead of disaster, the boat and engine worked together like a diazepam dream as the revs and speed built. Once in its sweet spot (over about 3,000rpm) the 3-cylinder engine smoothed out radically, and the Cathedral Hull both rode and handled great on plane, just as Mopar had advertised 48 years ago. Eyeing the lake’s far shore, we passed an aluminum skiff and its fishermen, who in turn eyed us suspiciously. Transporting our contraband cargo, I felt a surge of adrenaline – perhaps just as the rumrunners felt during Prohibition.

Soon we navigated through a narrow channel and around a point to find a perfectly deserted cove offering a broad, hard-packed beach, a protective rock formation to windward, lovely shimmering Aspens, and beyond them the very trails that had ignited my imagination a decade earlier. This was some kind of strange bike trip, but it was working out – so far.

Truly happy trails

To hold the boat while we were onshore, we’d come prepared to throw the anchor and a long scope of chain astern, and then run a bow line onshore to a log, tree or boulder. But when the Chrysler’s hull nosed onshore, conditions were so quiet that this seemed wholly unnecessary. As such, roped to the boat’s bow eye, the fluke anchor gripped the beach just fine, all afternoon. Unloading the bikes was the reverse of loading, except with the aluminum ramp angling to ground instead of the pickup bed.

Riding back and forth, up and down hills and side by side for photos revealed key differences between the familial Honda 90s. The SL90 ergonomics and suspension were way better than the CT90’s, but its street gearing and poor compression (it needed a new top end) meant it struggled to climb hills at this altitude. Call me surprised here.

Conversely, the loaner Trail 90 was an animal, offering crisp performance, better grip from its new universal tires, and importantly, a dual-range gearbox. Rather than struggling with road gearing, the selectable low-range gears helped the CT90 climb anything we encountered, easily. Its only downsides were less suspension travel and the absence of a gas tank to grip with your knees. With a rebuilt top end and lower gearing, the SL90 would rule the roost here. But today, the CT90 held court.

After we’d had enough beach riding, hill climbing and racing side by side on the jeep tracks, I broke away on the SL90 to finally live my high school dream, and explore a mystery. Years ago, an old-timer at the lake had explained that at the end of the Jeep track began a narrow trail that wound as far as you’d care to go toward the distant Sierra peaks. And that’s exactly what I went to find, leaving JG and Seth chilling on the beach.

Lord knows I tried to find it, riding to the absolute end of the jeep track, scanning the surroundings 360 degrees, and then parking the little Motosport and climbing a rocky escarpment for a better perspective. But the alleged single-track just wasn’t there – not that I could find, anyway. All that presented itself was hectares of forbidding rock, the kind that’s conquerable on foot – but not on a Honda 90.

They say man is empowered by victory, but that we learn more from defeat: I regard this trip as a blend of both. It proved that such an inane quest as using a castoff vintage boat to haul vintage bikes is not only possible, but practical and doable, too. It demonstrated that crucially, the vessel and bikes must fit perfectly together; in this regard, we were really fortunate. It showed the people involved must have the right makeup – meaning enthusiastic, flexible, creative and committed. And it reminded me that not reaching your absolute goal – in my case, finding a mythical trail into the towering Sierras – is no cause to quit.

Instead, it just made me hungry to try again. Only this time it will be with a fresh top-end on the SL90, carb jetting for 8,000 feet and gearing to match. Because of this first-ever “Vintage Boat Cross,” I felt the excitement then and still feel it now. Or more precisely, to paraphrase Flounder in Animal House: “Oh boy, is this gonna be great!” MC

Click here to learn what was used to get the Chrysler Sport Fury boat and Honda trail bikes ready for the trip across the lake and ride on the trail.

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