Difference between 1 and 2 cylinder outboards

[quickstep192]

I'm shopping for a new kicker for the sailboat. I want to reduce weight both to raise the ass end of the boat and to make it easier to remove, so I'm considering a 6hp to replace the current 8hp motor. While shopping, I noticed that Yamaha makes two different 6hp motors; one that's two cylinders and one that's just one cylinder. If both are 6hp, will the two cylinder model be able to produce more thrust than the single cylinder? Ordinarily, I'd incline toward the 2 cyl, but it's considerably heavier. Any thoughts on this?

[quickstep192]

For what it's worth, here are some specs:

Type: Outboard Motor
Year: Current
Model: F6 HP
Model Number: F6AMSH
Series: Four Stroke Portable
HP: 6
Engine Type: 2 Cylinder
Displacement: 8.5 ci
Compression Ratio: 8.9
RPM Range: 4500-5500
Fuel Delivery System: Carbureted
Fuel Type: Unleaded gasoline (minimum pump octane 87)
Exhaust: Thru prop
Ignition System: CDI
CARB Rating: 3-Star
Alternator Output at WOT: 6A
Starting System: Manual
Lubrication: Wet Sump
Gear Ratio: 13
Control Type: Tiller Handle
Trolling Throttle Adjustment: N/A
Cooling: Water, Thermostatic Control
Weight: 83 lb
Gear Shift: F-N-R
Command Link System: No
Enhanced Ultimate Corrosion Protection System UCP: Standard Feature
Power Trim and Tilt: No
Power Tilt: No
Shaft Length: 15 inch
Gearcase Rotation: Left Hand
Stop Switch Lanyard: Yes
Ultimate Corrosion Protection System: Yes
3 Year Limited Warranty: Yes
Thermostatic Cooling System: Yes
Aluminum Propeller: Standard
Tiller Handle Steering: Standard
Engine Sensing Warning System: Standard
High Output Alternator: Optional
Dual Thrust Prop: Optional
Shallow Water Drive: Standard





Engine Type : 1 cyl.
Displacement : 8.5 ci (139 cc)
Compression Ratio : 8.9:1
RPM Range : 4500-5500
Fuel/Induction System : OHV
Ignition System : CDI
Alternator Output @ W.O.T. : 6A **
Starting System : Manual
Lubrication : Wet Sump
Gear Ratio : 13:27 (2.08)
Shaft Length : 15 in., 20 in.
Weight : 60 lb (27 kg)
CARB Rating : 3-Star
Warranty : 3 Year Limited Pleasure Boat - 1 Year Limited Commercial
Mileage: 0

[Esmeralda]

quickstep192, what type of sail boat, and do you need an alternator that comes on both versions?

On the outboards, some are tuned down and weigh the same; so I would select the one that is tuned up.

I have a very small Honda 20 inch shaft 2 hp 4 stoke 1 cylinder I like, and it weighs 39 pounds

[Capt Crunch]

Maybe the thinking is along the lines of the reason my 3-cylinder 40hp Yamaha has THREE CARBS: If one craps out, maybe the other two will still work.

It never made sense to me if the question was simplicity or rebuilding carbs (why 3 instead of ONE?) but for safety's sake, it's redundancy I guess.

If you just had ONE carb (or ONE cylinder or spark plug or coil or coil wire or magneto pickup) ...

... versus TWO of each ...

... your chances of a disabling breakdown would be DOUBLED!

Having TWO instead of ONE cuts your risk of being completely disabled in HALF. You might limp, but at least you'd get home without sneakers and water wings.

If you plan to regularly use and/or maintain the motor, I would opt for two cylinders over one for this reason.

In a car, I would say just the opposite. But it's hard to walk home from broke boats.

[Fully_Loaded]

Maybe the thinking is along the lines of the reason my 3-cylinder 40hp Yamaha has THREE CARBS: If one craps out, maybe the other two will still work.

It never made sense to me if the question was simplicity or rebuilding carbs (why 3 instead of ONE?) but for safety's sake, it's redundancy I guess.

If you just had ONE carb (or ONE cylinder or spark plug or coil or coil wire or magneto pickup) ...

... versus TWO of each ...

... your chances of a disabling breakdown would be DOUBLED!

Having TWO instead of ONE cuts your risk of being completely disabled in HALF. You might limp, but at least you'd get home without sneakers and water wings.

If you plan to regularly use and/or maintain the motor, I would opt for two cylinders over one for this reason.

In a car, I would say just the opposite. But it's hard to walk home from broke boats.

The way a 2 stroke works is right behind the carbs are reed valves, if you ever take a 2 stroke apart you will notice the crank had channels cut into it, the fuel has to have a realitivly stright shot to the cylinder. The vacume of the piston pulls the fuel from the carb onto that channel in the crank, then the applied forces sling that fuel into the cylinders to atomize. That would not be possible with only 1 carb. best I can tell. As far as 1 vs. 2 cylinders it is probably marginal as far as the difference. The bigger you go on the motor the additional cylinders provide a longer lasting motor. As in you example of a 40 HP Yamaha, they make a 2 cylinder version and a 3 cylinder version. They are heavier but have to work less to provide the same HP. If you notice the 1 cylinder in these small motors have a slightly higher gear ratio. I would think you would get a pinch more torque out of the 2 cylinder since you have more rotating mass.

[Esmeralda]

Maybe the thinking is along the lines of the reason my 3-cylinder 40hp Yamaha has THREE CARBS: If one craps out, maybe the other two will still work ...

Had a 1979 75hp johnson stinger 2 stroke with 3 cylinders and 3 carbs. That motor ran for 20 years on a 16 foot aluminum starcraft bowrider and was gifted to a cousin for his pontoon boat after the boat wore out.

The only issue with that motor that occured, was a limp-home one time and it needed new rings on one of the cylinders; the carbs alway worked fine

[standup616]

Difference between 1 and 2 cylinder outboards ...................1 cylinder? http://www.youtube.com/watch?v=oeMwHZrUbVA

I couldn't resist \ but waited until a few serious and informative posts occured first!

[Capt Crunch]

The way a 2 stroke works is right behind the carbs are reed valves, if you ever take a 2 stroke apart you will notice the crank had channels cut into it, the fuel has to have a realitivly stright shot to the cylinder. The vacume of the piston pulls the fuel from the carb onto that channel in the crank, then the applied forces sling that fuel into the cylinders to atomize. That would not be possible with only 1 carb. best I can tell.

Hmmm...I had a 1973 Evinrude 40hp 2-cylinder that had only 1 carb...

[Fully_Loaded]

With a 2 cylinder it may be possiable because you can place the carb between the 2 cylinders and the reed valves would split the fuel.