Prop spin on Yamaha 25

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duckwhisperer

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I have a 88 yamaha 25 tiller steer motor. When in neutral the prop does not spin more than a couple revolutions when you spin it with your hand. My friend has a 25 Evinrude and it will spin several revolutions....even spin when he is towing it. I have spun mine really slow and it is a smooth as can be not gritty or have any "catches" in it. Is this something tobe concerned with? I know it will only push my 14ft polarcraft about 22mph and I think it should do better as I have the boat stripped bare. Could the resistance be costing me speed? Thanks for any input.
 
No fishing line just does not "freespool" in neutral....Just has slight resistance when you turn the prop. Not gritty even. Lower unit is in good shape oil is freshly changed and the old oil looked the same as the day it went in.
 
I don't think the small resistance you are explaining is causing you to lose speed....... as for your speed readings lets get some more info from you because 22mph with that setup does sound low.

What did you take your speed reading with?
What is your RPM reading at WOT?
What size prop do you have?

And does the motor sound like it slips (revs higher) while you are running it? Mark the rubber hub inside the prop before you go out next time and when you pull out of water check to see if the mark is still in line with the prop, this will tell you if prop hub is slipping.
 
Johny25 said:
I don't think the small resistance you are explaining is causing you to lose speed....... as for your speed readings lets get some more info from you because 22mph with that setup does sound low.

What did you take your speed reading with?
What is your RPM reading at WOT?
What size prop do you have?

And does the motor sound like it slips (revs higher) while you are running it? Mark the rubber hub inside the prop before you go out next time and when you pull out of water check to see if the mark is still in line with the prop, this will tell you if prop hub is slipping.
Motor is not slipping. I dont have a tach to take a RPM reading. The motor is an 88 model with the factory prop. I took the reading with my GPS. I had just a small amount of throttle left but it sounded like it was at a point that I wouldnt get much more out of it without over revving the motor.
 
Ok what you just described means it is very likely you are under propped. This would also explain low speed reading. Find out the prop size and post it. Also a tach reading would confirm my suspicion.

When/If you get the motor to top speed and there is throttle left and the motor revs higher and you get no more acceleration it typically will mean you have to low of a pitch on your prop
 
ok since you do not have a tach reading I will not guarantee the prop pitch is too low but if it is just you (200lbs) and the boat (250lbs) that the motor is pushing then it is very likely 11 pitch is too low. But without a tach reading I don't feel comfortable telling you to go up in pitch, the tach reading would tell exactly how much higher to go. Rough guess.....being you have a 2 to 1 gear case on that motor I believe would be a 13pitch....but that is a guess all be it and educated one.

I turn a 10X14 pitch with my 88' johnson 25 on a fairly loaded 14' boat..... 1200lbs total weight in my boat. I have a different gear case than that the yamy though so don't take that info to heart
 
You have a 25ESH, I assume. Twin carburetor/twin cylinder? Or....is it a C25 single carb/twin cylinder?

There is a BIG difference between the two. Without knowing which one you have, noone can give any reliable info.

How long the prop spins after turning it by hand is dependent on a LOT of things. Gearcase fluid temp, speed at which is was hand-spun, prop weight, etc. Inertia plays a big role here too...I just did an F150 prop swap (4 stroke 150 inline), went from aluminum 3x14x21 to a Turbo 3x14 1/4x23. Aluminum prop might make 2 revolutions if I spun it about as fast as I could. Turbo prop would spin....probably 25 revolutions, but keep in mind it weighs about 15 lbs as opposed to the aluminum's...what 6 lbs? Inertia is working.....
 
Same as a 25ESH (which is the newer model designation). Exactly the same motor, more or less.

Perfectly normal. Even my 4 stroke only stays spinning maybe a turn or so after I let go of it. Stock 9 7/8 x 11 1/4 Aluminum prop. I stuck a SOLAS SS prop on it once and of course as "normal" I gave it a spin after installation. 4...maybe 5 turns? It definitly spins a while by hand due to it's higher inertia.
 

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