question about rpm's

[screenbuzz]

i have a 115 evinrude v4 with a 13 3/4 x 15 pitch prop. when i'm at wot my rpm's run 6000. then when i trim the motor just before porposing it turns 7000 rpm's. is my prop to low of a pitch or could it be my tach is reading wrong. i have a teleflex tach. my switch position on tach is set between 5p and 6p i've tried changing the tach to 6p and it doesn't help. to my understanding this motor should be turning between 5000-5500 rpm's max. should i be running a 13 3/4 x 17 pitch prop to keep from over revving the engine? i know that it would increase speed by maybe a few mph. it's not worth the money to me for a few mph in speed but to save the engine from being over revved would be worth the money for a new prop. thanks in advance.

 

[12Footer]

Re: question about rpm's

It could be normal cavitation. It could be the hub is about to spin out. Not the most likely thing, but run it a few more hours before sending the prop in, to see if it gets worse.<br /><br />If it has allways done this, then chances are, you are right, it needs more prop.

 

[Ross J]

Re: question about rpm's

Sorry I made a **** up

 

[Ross J]

Re: question about rpm's

Hi screenbuzz,<br />I wonder if it would be worth having an expert check your prop out. I have a manual for this model which states it comes supplied with a 3 blade, 13" dia. x 19" pitch prop. it further states the WOT is 4500 to 5500rpm. I sounds as if you're underpropped.<br />Good luck<br />Ross

 

[MGuckin]

Re: question about rpm's

If the prop isn't spun, it is way under propped for the boat. Max hp is achieved at 5000 rpm. 2000 under what you can get out of it. Motor should never be revving that high. 1" of pitch is approximately 200 rpm difference. If it was me, I would check correct motor height and alignment, check prop and tach using a handheld tach to compare readings and go from there. If all readings and tests are ok, I would stick a 21 or 23" on it. Had the same problem a few months back and the advise I received here helped to cure my problem. Had a bad tach (replaced), motor at wrong height(to high) and to small of a prop.(went froma 19 to a 23).<br />Good Luck,<br />Mike