acts like a slipping clutch

Have a 1977 25Hp Johnson mod#25E77S. Runs fine at slow speed, if I give it the gas all at once the motor revs & we don't get forward motion. My first thought was the shear pin, pulled the prop & all is good. If I give it the gas slow & steady it runs fine, & the boat gets up on plane & gets to top speed with no problem. From slow speed if I give it the gas all at once it acts like a stick shift car when the clutch is slipping. Thoughts?
Thanks, John

Possibly a spun hub. Make a mark on the prop that aligns with the cotter pin locking the nut in place. Run the motor until you get the slipping condition, then check the alignment of the mark. If it changed, you've got a spun hub. You'll need to either replace the prop or re-hub it.

Also make sure that your lower unit is low enough in the water. The anti-ventilation plate should be just above the water line when at full speed. If not, you could be drawing air into the prop area (usually more of an issue at higher speeds)

Not many other conditions provide for a slippage without significant gear noise or rattling.

I'd check the hub first.

Good luck!

Clutch dog

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Am betting clutch dog as well. lightly place your hand on the shifter while accelerating hard and see if it pops back toward neutral. Be careful as it may pop back pretty forcefully.

Gonna test for a spun prop today, & move on from there. I will post the results. Should have mentioned this is a tiller motor.
John

Great.....you can do both tests at the same time.

Thanks to all who responded with help. I now know I have a spun prop.
Thanks again, John

LOL - would'a lost that bet! Good deal.....you can have it sent off if you want. Normal cost to re-hub and re-condition is around $60 or so down in this neck of the woods.