testing a motor without a prop

[burnt-clutch]

Would I hurt anything by running my HD25 or TN28 in a test barrel without a prop? I only have a 10 gallon barrel and I want to see how much water their impellors are pumping, but I’m afraid that all of the water slushing around is keeping them from getting a good flow. I pulled the plug out of the back of my HD25 yesterday and I only saw a trickle of water coming out of the back of the head when it was at mid range speed.
-Karl

[seakaye12]

Just don’t rev them up too much and you will be ok.

When a shop runs an outboard in their test tank at full throttle….they do so using special "test Props" which are designed to simulate the load of a conventional prop but "no splash"…..

[outboard315]

It is not recommended but I believe if you keep it below half throttle you should be ok. With the JW motors they changed props to stop them from over revving on light canoes.

[garry-in-michigan]

The higher RPM in the "no load" situation tends to lean out the mixture. It may be adjusted for a perfect slow speed idle, but sneeze and stop when shifted into neutral. An 1/8 turn to the rich on the idle adjustment will keep it from sneezing, but may result in a less than perfect idle in gear. Outboards are built on compromises. Cheap – Dependable – Fast – pick any two . . . 😆

[Pete]

Ok but keep the revs low and do it as quick as possible till you see what you want.

[outbdnut2]

No prop is not much different than revving up a gearshift motor in neutral, except most motors limit how far up you can run the throttle.
Dave

[Author]

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