Take Five: 1985-1991 Yamaha FZ750

Best bets on tomorrow’s classics: 1985-1991 Yamaha FZ750.


| September/October 2014



Yamaha FZ 750  1985

Yamaha FZ750

Image courtesy Yamaha

Yamaha FZ750
Claimed power: 85hp @ 11,000rpm (period test)
Top speed: 140mph (period test)
Engine: 749cc liquid-cooled 20-valve DOHC inline four
Weight: 494lb (wet, no fuel)
Fuel capacity/MPG: 30-50mpg
Price then/now: $4,599 (1985)/$1,500-$4,000

Sales people love something new to talk about. And in 1985, the plaid jacket guy at your Yamaha dealer could claim one-up on the competition. Their bikes only had four valves per cylinder. His new FZ750 had five. More is better, right?

Well, maybe. The move to 3- and 4-valve cylinder heads was spurred by a need for more efficient combustion (read: lower emissions) while using higher compression ratios (for higher performance) but running with the new, lower-octane unleaded fuels. More valves also meant a lighter valve train allowing higher revs while maintaining good gas velocity at low revs for tractability. But five? As the only manufacturer going for the handful, Yamaha had something to prove.

And prove it they did. In the new FZ750, the 20-valve Genesis engine churned out 85.3 horsepower at a screaming 11,500rpm on Cycle magazine’s dyno. It also tore up the quarter-mile strip in 11.4 seconds at 117mph, and hit 60mph in less than three seconds. “It’s hard to conceive of this level of power from an over-the-counter 750 engine,” Cycle’s editors said, adding, “yet the FZ delivers the goods so eagerly it makes other 750s seem as if they belong in a race for freight elevators.” And it wasn’t all top end power. “The engine is remarkably tractable, too, considering its high specific output, and that’s largely due to the copious midrange. Usable power comes on at 3,000rpm and builds smoothly to the 11,000rpm redline,” Cycle Guide said.

All this grunt came from an inline 4-cylinder with chain-driven dual overhead camshafts, 11.2:1 compression and the aforementioned 20 valves. Each cylinder had three 21mm intakes and two 23mm exhausts arranged radially in a shallow “biconvex” combustion chamber and adjusted by under-bucket shims. The 68mm pistons ran in “semi-wet” iron liners (with coolant contacting the liners only near mid-cylinder), connected to a crankshaft with a 51.6mm stroke. Drive to the 6-speed transmission was by straight-cut gears and a wet multiplate clutch. The 300-watt alternator was piggy-backed on the crankcase to minimize engine width.

The drivetrain was slotted into a square-section steel tube perimeter frame with the cylinders canted forward at 45 degrees, allowing the four 34mm downdraft Mikuni CV carbs to breathe cool air from above the engine in front of the gas tank, while also providing an almost straight intake tract. The forward slant also gave the FZ a lower center of gravity, and, Yamaha hoped, would help mitigate the familiar inline 4-cylinder engine buzz by changing the plane of primary vibration.





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