How to get a few more rpm from my engine?? Please Help...

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stant1man

Petty Officer 1st Class
Joined
Jul 21, 2004
Messages
360
Hi folks,<br /><br />I'm trying to get and extra 300 or so rpm from my stainless prop. Its a 13 x <br />18p originally off a Yamaha but fitted like a glove. It currently revs to <br />5000rpm when loaded and 5200rpm with just me and a passenger. 42mph tops.<br /><br />Are there any tricks without changing pitch to get a little more rpm out of my motor. It used to be an 1150 before i made some changes to make it a 1350.<br /><br />I've heard about drilling the prop, whats that about?<br /><br />I put .080 jets in the carbs, would changing to .0785 make any difference.<br /><br />Many Thanks<br /><br /><br />Stan
 
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walleyehed

Admiral
Joined
Jun 29, 2003
Messages
6,767
Re: How to get a few more rpm from my engine?? Please Help...

Drilling or "Venting" the prop is for hole-shot.<br />What jets did you have, and what does the 135 call for, or do you have the 115 carbs on it???<br />Is the engine mounted clear down on the transom???
 
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stant1man

Petty Officer 1st Class
Joined
Jul 21, 2004
Messages
360
Re: How to get a few more rpm from my engine?? Please Help...

The carbs on the 1150 and the 1350 are the same, the only difference between the two are reed stops, carb venturis and main jets at 0.0785. I put in 0.080 for 2 reasons - <br /><br />1. I didn't want to lean off a freshly rebuilt engine.<br />2. I figured with the colder climate here in Scotland it would have worked out about right.<br /><br />Average temp here is 12-15 degree c at the moment. I will try the other jets to see if there is any difference.<br /><br />The top of the lower unit is slightly above the bottom of the transom but i know little about what it should be.<br /><br />Thanks<br /><br />Stan
 
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ob15

Chief Petty Officer
Joined
Jan 4, 2004
Messages
514
Re: How to get a few more rpm from my engine?? Please Help...

When you say <br /><br />
The top of the lower unit is slightly above the bottom of the transom
Click to expand...
What part of the lower unit are you refering to? When we ask that question we are talking about the anti-ventialtion plate (AV plate). It is the horizontal plate above the propeller. Where is that in relationship to the bottom of the boat?
 
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