Neewbie with a stupid question...

Redneck101

Redneck101

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Feb 22, 2010
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:( Just bought a 15' 1987 150 Sierra Starline ski boat w/ mercruiser mcm120 i/o. it has a 19 pitch on it but he said he changed it about 6 months ago and doesnt remember what it had. how can i find out if what prop i need. boat barely planes out as it is and top speed of 28 mph shouldnt this boat go faster? and also when u grab the prop it moves anot a 1/4 inch in and out. could he have put the wrong prop on to cause this. idk what the wot rpm should be or where to find it.... please help. :(
 
180shabah

180shabah

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Mar 26, 2005
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Re: Neewbie with a stupid question...

The WOT spec for your engine is in the manual you need to download. It is free. Prop selection will be based on your current performance AND that spec.

But it is irrelevent until you are sure you have a properly running engine WITH cooling water.
 
Redneck101

Redneck101

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Feb 22, 2010
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Re: Neewbie with a stupid question...

180shabah said:
The WOT spec for your engine is in the manual you need to download. It is free. Prop selection will be based on your current performance AND that spec.

But it is irrelevent until you are sure you have a properly running engine WITH cooling water.
Click to expand...

Very true but i am still trying to decide if it is worth it to fix this boat or find another.
 
Bondo

Bondo

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Re: Neewbie with a stupid question...

top speed of 28 mph shouldnt this boat go faster? and also when u grab the prop it moves anot a 1/4 inch in and out.
Click to expand...

Ayuh,... It might break 30mph,... About 1/8" to 3/16" fore-/- aft propshaft movement is Normal...
 
S

steelespike

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Apr 26, 2002
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19,069
Re: Neewbie with a stupid question...

Do you have the current rpm?
Shooting from the hip a 15 foot with a 120 I/O should run about 40+ mph at about
4,200 to 4,600 rpm.with a 21" pitch.With reasonable to exceptional hole shot.
Something is up with your rig.Don't panic.Check the compression,check that it is running on all cylinders,be sure the throttle opens all the way.Be sure it is in excellent tune.Your rpm rating may be on a label on the motor.Let us know what you find.
 
Redneck101

Redneck101

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Feb 22, 2010
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Re: Neewbie with a stupid question...

I will. It got a little cold down here the last few days but i plan on gettin back into it sunday. Thanks..
 
Texasmark

Texasmark

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Dec 20, 2005
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14,665
Re: Neewbie with a stupid question...

Nothing to do with the answer, but as for the question, there is no such thing as a "stupid question". If it weren't important you wouldn't bother asking.

I agree with the other guys. You have something dreadfully wrong with your engine. I had a 120 on an 18' boat and could do 35 without even blinking with a boat full of Sunday fun things.

Mark
 
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