Sould I re-jet and/or change prop pitch? 10E76H

12" aluminum boat with a 1976 9.9 Johnson. The boat planes easily with one person. When I get the wife and kids in there it won't plane. I am currently running the stock 9 1/2 X 10 prop. Should I make a pitch change to get better all around performance?<br /><br />I live at 2000' altitude, but will sometimes be going to lakes that are at 6-7,000'. Do I need to jet down for this altitude? My carb has no high speed carb adjust, only low speed. any ideas if I will need to re-jet or if I do need to re-jet, what size jet, without hurting the motor?<br /><br />Thanks

Re: Sould I re-jet and/or change prop pitch? 10E76H

1 size smaller jet (.001) per 2000ft above sea-level would be standard.<br />The timing needs to be advanced 1 degree per 3000ft, on all mechanical type systems (non-OIS) which the '79 falls into the standard mechanical catagory.<br />Word of caution: You MUST remember to increase jet size and retard timing before operating back at original altitude!!<br />Also, on the prop, if you are turning recommended WOT at your present altitude, to maintain the same rpm you drop about 2" in pitch for every 3000ft change up-hill.

Re: Sould I re-jet and/or change prop pitch? 10E76H

The prop you are using is probably the 2 blade weedless. The OMC 3 blade prop 174938 is 9.25 X 8 which would get you out of the hole quicker and lift more load. <br /><br />Try here and scroll down: web page

Re: Sould I re-jet and/or change prop pitch? 10E76H

Thanks for the replys:<br /><br />Walleyehed- Are these jets availabe at most johnson marine centers? are these motors altitude sensative, what I mean, are they jetted for sea leval and anything over 4,000' is going to foul plugs without out re-jet? Will I have to re-jet for sure to run at 6-7,000'? Or do these motors run at altitudes up to some elivation before re-jetting is in order?<br /><br />Ezeke- This is to my knowledge, the stock 9.5X10 3 blade aluminum that came standard. I am unsure if it's weedless or not. <br /><br />Thanks for the help.<br /><br />Randy

Re: Sould I re-jet and/or change prop pitch? 10E76H

You may be asking a little much of that motor to plane out with the load you're carrying.

Re: Sould I re-jet and/or change prop pitch? 10E76H

Doesn't make any difference, Randy. Pitch is the theoretical distance in inches that the boat would move in one revolution of the prop. The lower pitch prop gives greater power but lowers the theoretical top speed of the boat.<br /> <br />Theory is nice but if you can't get on plane, hey!

Re: Sould I re-jet and/or change prop pitch? 10E76H

Randy, you can run ok to about 4000ft before you need to consider jetting and timing changes on 1-time trips...to go above 6000ft, you will atleast need to step down .002 in jet size.<br />At 6000ft. you're only getting about 8HP at best, on a good day.

Re: Sould I re-jet and/or change prop pitch? 10E76H

Thanks for ALL of your help. I wish the main jet was easier to replace than it is. I will see about buying a smaller jet and bring it with me to the high elevation trips.<br /><br />Get this, I went to my local boat prop place ("gotta have it prop shop" in Moreno Valley, Ca.) and the guy was telling me that changing the pitch or diameter of the prop will do nothing to help me at all.<br /><br />I'm not a complete idiot and understand what I'm asking of a 9.9 to do, but i find it hard to believe that I wouldn't see any difference by changing prop pitch and/or size.<br /><br /><br />I think reducing my prop's pitch would allow my motor to make a little more RPM out of the hole and help to get me on plane, but I will also loose some on top end speed. That's how I was taught.<br /><br />Thanks again for all the help

Re: Sould I re-jet and/or change prop pitch? 10E76H

And that is correct, Randy, (what you were taught).Follow the guide-lines you already understand, and come back here if ya need some help..there's some good folks here.<br />Good luck and have fun!