Enough power?

[garry-in-michigan]

Please confirm transom hight – It should be 20 to 22 inches for a long shaft motor. . . 😕

[jerry-ahrens]

I think the first thing I’d do is find out what pitch prop you have. As a reference, my 14 ft Alumacraft with a 35 Gale, is turning a 13 pitch brass Michigan prop at the proper RPM’s. i tried a 14 pitch, but it was too much, and planned out slower with less top end power. With a 400 plus pound boat with a 28 hp engine, I would think a lower pitch prop would be needed… maybe even an 11 pitch?? All boats are different though, and you really need a tachometer hooked up to the motor to see what it’s turning.
keep in mind that 2 cycle engines can’t make their rated H.P. unless they are turning at the specified rpm,s they are rated at. In other words, a motor that is being lugged due to a wrong pitch prop, or to much weight in the boat, etc. will not allow the engine to reach it’s full power potential.
Or, maybe the 28 motor is just not enough ? If you have a long shaft transom and a 40 hp max rated boat, then you may just need more motor. Maybe a picture of your boat/motor combo would help us give a better opinion.

[chinewalker]

To add to above, your motor has a throttle advance in addition to the cam under the mag plate. It’s a rod attached to the carb linkage and advance arm. Make sure it’s advancing fully and getting the carb butterfly to fully open.

[fleetwin]

quote mikeg:

Boat is rated for up to 40hp, long shaft motor on long shaft transom.
It has never sounded like it’s “winding up”. What should I look for to increase RPM,
besides prop?

The prop might be your issue, so don’t overlook it….What pitch prop are you using?
This engine has a strange synchronization feature referred to as the enconomizer linkage. If not set up properly, the butterfly may not be opening completely. Do you have a manual for the engine? If not, perhaps someone can post the setup instructions online for you….

[outbdnut2]

quote outbdnut2:

Going to a short shaft motor for your short shaft transom should get you at least another 5 MPH – you are essentially dragging a 5 inch club through the water. I’ve seen blocking the motor up the thickness of two paint stir sticks (about 1/4 inch) give a 35 HP motor another 2 MPH on a lightweight 14′ aluminum runabout. Gas mileage will increase too.
Dave

Sorry, I must have read your earlier post wrong – somehow I was thinking you had a short transom. disregard my comment above.
Dave

[mikeg]

This is a long shaft motor on a long shaft (20") transom.
Prop is the standard 103/8 x 121/2 which came on the motor when new.
Thanks for all your help. Will take a look after the weekend is over and
have the time to do more investigation.
Mike

[billw]

I’m with PhilB. Sounds like running on one cylinder to me, too….

Long live American manufacturing!

[jeff-register]

Compression?

[garry-in-michigan]

OK – the less of the lower unit in the water, the less drag. I often run a 16"+ transom height on a light boat. The limiting factor is the propeller. It must be deep enough to get traction. It needs the most traction getting on plane. Turning pushes the back of the boat at an angle. This lifts the outside edge of the boat and brings the propeller closer to the surface. For this reason, it is apt to break loose on turns if raised too high. The propeller has a great deal to do with the speed. Thin blades have less drag, but for the same material have less strength and are more easily dammaged. Brass blades are stronger, more rugged and easily repaired. They are also heavier and may hasten shifter damage. Stainless steel is strongest, but expensive to build and repare. A damaged propeller on an outboard is like a flat tire on a truck. The more damage the less efficiency.

What would cause a loss of power in an outboard? Stuck piston rings and scored (Worn) pistons has been discussed and these are usually caught by a compression check. Chrysler published a compression figure for it’s outboards, OMC never did. The figures we guesstimate have been found by trial and error. (Probably more error than necessary.) This cannot guarantee a good crank case compression. Any leaks from loose bearings, dammaged piston skirts, Broken reed valves, bad seals or leaking seams may not show up on a compression test. Bad bearings or components out of alignment may cause horse power robbing friction. Water pump damage or gear case problems may be at fault. Skeg damage may also damage the drive shaft alignment causing excessive friction. The drive shaft breaking at the water pump drive pin hole is a bad sign.

I am sometimes amazed at the amount of damage an outboard can sustain and still run. I had one Big Twin come in with complaints of fouling spark plugs. He had replaced a box of spark plugs over a weekend of fishing. It turned out it was broken bits of needle bearings that were doing the dirty work, but the motor still brought him back to his dock many times. Another was brought in with complaints of an oil leak. The motor seemed to run OK but had a rough idle. I found a broken connecting rod screw head had pushed through the crankcase leaving a 1/2" hole. The hole was covered by the counterweight during crank case compression so it still ran. I was amazed it held together with only one screw holding. Both these powerheads were replaced under warrantee. . . 😉

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